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Average Familiarity

Average Familiarity

https://www.xkcd.com/2501

https://www.explainxkcd.com/wiki/index.php/2501:_Average_Familiarity

[Ponytail and Cueball are talking. Ponytail has her hand raised, palm up, towards Cueball.] Ponytail: Silicate chemistry is second nature to us geochemists, so it's easy to forget that the average person probably only knows the formulas for olivine and one or two feldspars. Cueball: And quartz, of course. Ponytail: Of course. [Caption below the panel] Even when they're trying to compensate for it, experts in anything wildly overestimate the average person's familiarity with their field.

This comic claims that experts vastly overestimate how familiar other people are with their own field of study. As an example, Randall shows a conversation between Ponytail and Cueball as two geochemists specializing in silicate chemistry. Although the two scientists understand that the layman does not know all that they know about silicates, they are still under the impression that other people at least know the chemical makeup of olivine and some feldspars . Cueball also mentions quartz , an even simpler mineral taken for granted by Ponytail. In truth, the average person can't be expected to know the chemical makeup of any arbitrarily-chosen substance reliably (or any material at all), if that average person's job and hobby do not involve chemistry — aside from the few that made their way into common knowledge , like NaCl for salt [1] (sodium chloride or halite in mineral form), H 2 O for water (facetiously known as dihydrogen monoxide, ice in mineral form), or CO 2 for carbon dioxide (while most people are more familiar with its gaseous form, it is also used in mineral form as dry ice ), and may not even know the definition of "feldspar" beyond "a mineral", if at all. It even goes so far as to initially gloss over the 'everyday' knowledge of quartz... until prompted by the slightly-less-overestimating partner in the conversation. Perhaps like a gardener forgetting to mention the lawn he maintains (along with the 'actual' plants in the borders or vegetable patches), there seemed no need to include such a common mineral as a subject of silicate chemistry. Quartz is a basic silicon oxide (SiO 2 ) that many non-chemists have heard of because it is common and has a variety of uses, though they would not know its chemical structure. Quartz can be found as distinct large-scale crystals (probably obvious to the layman, as an ice-cube is in a drink) but also features as a hard-wearing micro-constituent of many rocks. Quartz is a major component of most sand (except for coral sands, which are calcium carbonates). Quartz crystals are sometimes made into jewelry and other decorative objects. Most modern clocks use the resonance frequency of quartz to keep time. Minerals like feldspars and olivine generally exist as a continuum of varying chemical formulas, represented as a mixture of "endmembers" that have some pure composition. Feldspars are a category of aluminum-containing silicate minerals that account for the most of the rock in the earth's crust by mass. They are composed of a silicon-aluminum-oxygen lattice filled with sodium, potassium, or calcium ions. The major varieties are CaAl 2 Si 2 O 8 (anorthite), NaAlSi 3 O 8 (albite), and KAlSi 3 O 8 (potassium feldspar). Olivine is most notable as being the primary constituent of the upper mantle and commonly found in stony meteorites, and has the formula X 2+ 2 SiO 4 , where X is any iron or magnesium ion. The ends of the spectrum are Mg 2 SiO 4 ( forsterite ) and Fe 2 SiO 4 ( fayalite ). In the title text the two geologists express belief that the average person should be more familiar with silicates because of how ubiquitous they are. Their somewhat-exasperated statement plays on the phrase "you can't throw a rock without hitting one," a standard hyperbole about how common something is. Indeed, silicate rocks are extremely common on Earth — not only would a rock thrown in a random direction stand a decent chance of striking a silicate mineral rock, but the rock being thrown also has a very high chance of being a silicate mineral rock. With the exception of a few carbonate deposits, rocks found in large deposits on Earth's surface nearly all have silica in them, even extraterrestrial rocks. The Earth's crust is about 60% silica by weight. [2] [Ponytail and Cueball are talking. Ponytail has her hand raised, palm up, towards Cueball.] Ponytail: Silicate chemistry is second nature to us geochemists, so it's easy to forget that the average person probably only knows the formulas for olivine and one or two feldspars. Cueball: And quartz, of course. Ponytail: Of course. [Caption below the panel] Even when they're trying to compensate for it, experts in anything wildly overestimate the average person's familiarity with their field.

Every Data Table

Every Data Table

https://www.xkcd.com/2502

https://www.explainxkcd.com/wiki/index.php/2502:_Every_Data_Table

[A data table is shown with eight years given. After each year is seven dots. At the end of these dots are unreadable text/scribbles. The table is slanted compared to the panel, so the top year is in the top left corner, partly obscured by the panel, and the dots end at the edge of the panel, so only very small part of the scribles are seen (resembling an eight dot). And at the bottom the year is close to the middle of the panel, but most of the year is below the panel, and only the last three dots are visible. Two years have symbols indicating an unseen footnote.] 2017....... 2018....... 2019....... 2020*...... 2021 † ....... 2022....... 2023....... 2024....... [Caption below the panel:] Every data table from now on

This comic is another entry in a series of comics related to the COVID-19 pandemic . It shows a future data table with one entry for each year from 2017 to 2024, so this table is made at least three years after publication of the comic (presuming it does not depict some form of advanced estimation of trends). The only discernable differences across the eight years are that two years have footnotes as in 2020* and 2021 † , whereas the other six years have not. Sometimes a symbol such as an asterisk (*) or a dagger (†, also called an obelus or obelisk) is used to denote an unusual entry in a table to be explained in a footnote with a matching symbol. The COVID pandemic has had a large impact on the entire world and one way this can be seen is through strange stats resulting from the effects of the pandemic, at least in 2020 and 2021, the years marked with footnote in the data table. Various statistics such as employment statistics, spending power, holiday miles, pet ownership, births (or at least conceptions), and — naturally — deaths may have been either grossly suppressed/increased for the majority of 2020, and for 2021 may have hardly recovered, partially recovered, renormalized, bounced back with a vengeance or be over-compensated for in the effort to catch up. Thus Randall concludes that every data table will look like this one from now on, hence the title of the comic. In the title text Randall states that he hopes 2022 is relatively normal. Comically, he doesn't mainly hope for this because he wants the Covid-19 pandemic to end, but rather because he doesn't know what symbol is used after the asterisk and the cross. It is hard to know what 2022 might be like. Nothing (at the time of this comic being published in August 2021) is exactly back to normal and proper recovery or the resulting compensatory readjustment may not have concluded in time for 2022 to reflect the trends expected based upon pre-2020 figures, and the additional further years that future statistics will record. Common symbols that are used if the first two are taken include multiple symbols (such as †† or ***), or a series of further single-symbols such as the convention to use a double dagger (‡), the section symbol/silcrow (§), the parallel/double-pipe (‖) and the paragraph symbol/pilcrow (¶). Alternately you could just start and continue the series with superscript numbers (¹, ², ³ ...), especially when you discover a need to frequently clarify multiple and/or nested footnotes on each page, or save up a whole chapter of many such references to present them as 'endnotes', upon entirely different pages from the text being referenced. Unrelated to the usage as English footnote characters, the asterisk and dagger symbol are used in German mainly as the shorthand genealogic signs to express "born" and "died" respectively (e.g. in encyclopaedias, as the German terms are three-syllable words for both and need to be shortened), so a person that is 2020(*) and 2021(†) would have been alive for only about a year, depending on the months. This symbology is also used on some tomb stones. An optimistic view is the "birth" and "death" of the Coronavirus itself, which would also understandably result in uncertainty on the next symbol in this order, for 2022. Pessimists in this context might suggest to use ∞, which is the symbol for infinity. Similarly, in biology, species (or genus, etc...) that are possibly extinct are indicated with an asterisk and dagger is used to note the possible extinction (double asterisks indicate taxa believed to be extinct in the wild but known to be extant in cultivation). This of course do not fit well with the Covid-19, which is not close to extinction, and it is also not about to cause the extinction of humans. Randall, however, seems to have forgotten the potential monkey's paw nature of his wish. 'Relative' requires a comparison between things. It could well be that the whole fall-out of the pandemic becomes the new normal, and future years have no necessity to use symbols to explain how those years come to be like everyone knows they are, while dates before 2020 will be entirely understood as the old-normal. Only 2020 and 2021 may need contextual clarifying, due to the necessary transition/limbo between the earlier unaffected and later fully-adapted scenarios. [A data table is shown with eight years given. After each year is seven dots. At the end of these dots are unreadable text/scribbles. The table is slanted compared to the panel, so the top year is in the top left corner, partly obscured by the panel, and the dots end at the edge of the panel, so only very small part of the scribles are seen (resembling an eight dot). And at the bottom the year is close to the middle of the panel, but most of the year is below the panel, and only the last three dots are visible. Two years have symbols indicating an unseen footnote.] 2017....... 2018....... 2019....... 2020*...... 2021 † ....... 2022....... 2023....... 2024....... [Caption below the panel:] Every data table from now on

Memo Spike Connector

Memo Spike Connector

https://www.xkcd.com/2503

https://www.explainxkcd.com/wiki/index.php/2503:_Memo_Spike_Connector

[A memo spike is shown (a device also called a Spindle). It is a long spike standing up from a round base plate. A wire is coming in from the left and appears to be hardwired into the spike's base element. Two other wires comes in from the right. Both are firmly impaled down upon the spike, penetrated completely through shortly before their apparently unterminated ends. The end of the impaled wire closest to the base faces out and the details appear to show it to be of some variety of multicore (rather than co-axial) manufacture. The other cable's end is a bit higher and points into the image. Above is a title and below is a label.] Cursed Connectors #102 The Memo Spike

This is the third installment in the series of Cursed Connectors and presents Cursed Connectors #102: The Memo Spike. It follows 2495: Universal Seat Belt (#65) and was followed 9 days later by 2507: USV-C (#280). The comic depicts a large metal spike with a wire coming from the base. The spike stabs through two other wires, thus creating an electrical connection between the three. As the name suggests, the spike resembles a stationery spindle , colloquially known as a spike, called a Memo Spike here by Randall. However, unlike normal spindles, this one has a cable of some kind coming out of it, suggesting this is a hub of some sort. Spindles are used to temporarily hold paper by "spindling" or impaling the paper onto the spike (as depicted in the comic). They're most known for their use in restaurants as a way to hold bills that have been paid, or traditionally in offices that work with many bits of paper, e.g. with invoices in a finance department or hardcopy in newspaper editing, to prevent accidental disturbance/shuffling, at the expense of a small puncture mark in each sheet so impaled. (This could cause errors in papers with punch-holes that are meant to be read by machines, hence the admonition against " folding, spindling, and mutilating ".) In the latter context, the editor might put all the rejected stories onto a spike (rather than into a wastebasket) to prevent them going astray, and this might be the source of the term ' spiked '. The joke of the comic is while any number of non-destructive connection standards exist, a large spike can provide much of the same results: a conductive object that retains a connection of multiple wires in a way that allows electricity to pass through. Indeed, in the early days of Ethernet, vampire taps were used, essentially spikes that bit into a cable to establish a new branch in the network. Another type of connection which involves piercing the wire is a punch-down block , a type of insulation-displacement connector , where one or more wires are pushed into a cutting channel instead of onto a spike. Depending on the type of cable it is also likely to create a short circuit, e.g. by connecting both strands of a twisted pair of strands in a typical Ethernet cable, or the central wire and the sheath of a coaxial cable. In an enterprise environment, this could even happen on a PoE-Connection , which actually carry more noticeable amounts of power (up to 25.5W). Even if this is avoided, the single spike may be large enough to mechanically sever a random subset of the finer strands that exist within a multicore cable such as is commonly in use today. The title text takes this a bit further. It says that it is backwards compatible with many existing cables. This means any cable large enough to be impaled by the spike could be used. Needless to say it will likely not work anyway. It also continues by saying that phones and tablets can also be connected using this method if you press them down hard enough over the spike. Thus if you actually manage to make the spike penetrate the device's coverings to reach the electrical parts, then there is a connection. The implication is that any device or cable can be connected to any other device or cable as a form of universal adapter/splitter/combiner across arbitrary hardware and communications/power standards. In reality, this could be even more dangerous and will surely destroy the phone/tablet either directly or by overloading their cable connection. [ citation needed ] Also be careful not to impale your hand while trying to push the spike through your tablet's screen. [A memo spike is shown (a device also called a Spindle). It is a long spike standing up from a round base plate. A wire is coming in from the left and appears to be hardwired into the spike's base element. Two other wires comes in from the right. Both are firmly impaled down upon the spike, penetrated completely through shortly before their apparently unterminated ends. The end of the impaled wire closest to the base faces out and the details appear to show it to be of some variety of multicore (rather than co-axial) manufacture. The other cable's end is a bit higher and points into the image. Above is a title and below is a label.] Cursed Connectors #102 The Memo Spike

Fissile Raspberry Isotopes

Fissile Raspberry Isotopes

https://www.xkcd.com/2504

https://www.explainxkcd.com/wiki/index.php/2504:_Fissile_Raspberry_Isotopes

[Ponytail and Cueball are standing in a field, looking at rows of crops disappearing in the distance over rolling hills.] Ponytail: I reckon it'll be a good harvest. Ponytail: So long as we don't get too many fissile raspberry isotopes. Cueball: Too many whats ? [In a half height panel is shown a picture of a raspberry with an arrow to a situation where it is splitting in to two equal parts. From the split there also comes two small drupelets flying out as shown with arrows. Below these two situations is a smaller sketch of how one of these two drupelets will eventually hit another raspberry, which will send out three drupelets when splitting, two of those hitting other berries, that each send out two drupelets. The lower of these are not depicted hitting any, but the upper split hits two again, which each send out two, in an ongoing chain reaction. The depiction stops there. Above this panel is what Ponytail tells Cueball:] Ponytail (narrating): If a raspberry breaks in half, it releases fragments which can cause more splits. Within seconds you've lost the whole crop. [Ponytail and Cueball are standing in an empty panel talking.] Ponytail: Luckily the berries are bound by fresh raspberry pie mesons. Cueball: I hope they hold. Ponytail: It's my grandma's recipe. They'll hold.

Ponytail is admiring her raspberry fields telling Cueball she expects a good harvest... That is if they do not get too many fissile raspberry isotopes! To which Cueball has to ask Too many whats? The comic is thus a joking analogy to nuclear chain reactions , in which the fission (splitting in two) of one atomic nucleus releases neutrons , which then strike other nuclei and cause them in turn to fission, releasing more neutrons. This chain reaction releases a great deal of energy and is what makes possible both nuclear power and nuclear bombs . A fissile isotope , such as uranium-235 , is one that is sufficiently large and unstable to undergo such a chain reaction, as opposed to the more common and less unstable uranium-238 . Ponytail fear that her raspberries have too many unstable isotopes so that her fields risk undergoing a similar fission-driven chain reaction. This chain reaction is depicted in the second panel, and she explains that if this happens the entire crop may be gone in seconds. It sounds like this is only dangerous for her economy, i.e. all the berries destroyed, but not a runaway explosion that destroys her field and any living thing nearby. In real life, raspberries don't undergo such chain reactions. [ citation needed ] As an aggregate fruit , raspberries (as well as blackberries mentioned in the title text) resemble common depictions of atomic nuclei , with each drupelet corresponding to a nucleon (proton or neutron), which is probably why they are the subject of the comic. (The actual "appearance" of atomic nuclei, in contrast to the common depictions, is complicated by Heisenbergian uncertainty, quantum effects, and strong nuclear force interactions.) Perhaps these raspberries are byproducts of the experiments depicted in 1949: Fruit Collider . This comic is also a pun on "pi mesons" or pions , subatomic particles that transmit the strong nuclear force , and the similarity in name to a pie , the food type, as in a raspberry pie . The transmission of the strong nuclear force happens most importantly in the atomic nucleus and is responsible for keeping the nucleus intact, i.e. , preventing it from undergoing fission despite the strong repulsive electromagnetic force present from all the positively-charged protons . Raspberry pies (and pie mesons of such) are not to be confused with Raspberry Pi , a very popular microcontroller widely used for hobbyist or educational projects. Ponytail claims that her berries are protected (bound) by fresh raspberry pie mesons. Cueball states he hopes they hold, but Ponytail is confident as these pies are made from her grandma's recipe, i.e. , it is actually a fresh pie made from the berries. The faith in the pie recipe being able to impede the danger references the convention of "Just like Grandma used to make", nostalgia for an infallible cookery ancestor, in this case a hallowed family recipe that acts to mitigate any budding 'berry' chain-reaction. Grandma's baking is not always so fondly remembered and, in this case, it could be some (in)famous inertness and solidity to the product that is reassuring, not any form of culinary excellence. The title text mentions that the grandma's "blackberry pie meson" recipe was a huge seller, but that then the farm was shut down by a joint FDA/NRC investigation. This refers to the Food and Drug Administration (FDA) and the Nuclear Regulatory Commission (NRC). The FDA is responsible for the regulation and inspection of food in the U.S., and the NRC for the regulation and inspection of nuclear facilities and materials. A hypothetical "blackberry pie meson" might well run afoul of both, being both nuclear and therefore subject to NRC regulations and permitting requirements, and unhealthy to eat and thus violating FDA rules. This could in addition also violate the FDA's rules on radiation emitting products. One might be able to imagine the FDA discovering that the blackberry pies are functioning to contain a nuclear chain reaction, and calling in the NRC to consult. The FDA took a similarly incongruous interest in physics in the title text of 2216: Percent Milkfat . It is mentioned that the pies were shelf stable , which means it can last a long time without being in a refrigerator. This may be because of its innate radioactivity keeping it free from germs. This may also explain why they were shut down by both the above-mentioned agencies. The word "stable" also describes atoms , and therefore substances, that do not spontaneously undergo nuclear decay, though a stable isotope may (eventually) result directly from the decay of an unstable one. [Ponytail and Cueball are standing in a field, looking at rows of crops disappearing in the distance over rolling hills.] Ponytail: I reckon it'll be a good harvest. Ponytail: So long as we don't get too many fissile raspberry isotopes. Cueball: Too many whats ? [In a half height panel is shown a picture of a raspberry with an arrow to a situation where it is splitting in to two equal parts. From the split there also comes two small drupelets flying out as shown with arrows. Below these two situations is a smaller sketch of how one of these two drupelets will eventually hit another raspberry, which will send out three drupelets when splitting, two of those hitting other berries, that each send out two drupelets. The lower of these are not depicted hitting any, but the upper split hits two again, which each send out two, in an ongoing chain reaction. The depiction stops there. Above this panel is what Ponytail tells Cueball:] Ponytail (narrating): If a raspberry breaks in half, it releases fragments which can cause more splits. Within seconds you've lost the whole crop. [Ponytail and Cueball are standing in an empty panel talking.] Ponytail: Luckily the berries are bound by fresh raspberry pie mesons. Cueball: I hope they hold. Ponytail: It's my grandma's recipe. They'll hold.

News Story Reaction

News Story Reaction

https://www.xkcd.com/2505

https://www.explainxkcd.com/wiki/index.php/2505:_News_Story_Reaction

[Cueball is sitting at a desk, typing on his laptop. What he types is shown above Cueball, as indicated by the line going from his hands to the text.] Cueball: Devastated to hear that a pack of wild dogs got into the Louvre and shredded the Mona Lisa. Cueball: What a loss for humanity. Cueball: My first kiss was in the aisle of a J.C. Penny [ sic ] that had a poster of the Mona Lisa on the wall, so this is hitting me especially hard. [Caption below the panel] Sometimes I have to remind myself not to make every news story about me.

In this comic, Cueball is at his computer, likely typing a comment after reading a shocking news story where the Mona Lisa has been attacked and shredded by a pack of wild dogs. The Mona Lisa is one of the most famous paintings in human history. At the time of this comic, the Mona Lisa has not been attacked and is unlikely to be shredded in this circumstance at least by dogs as it is painted on wood, rather than canvas. [1] At the beginning of his comment, Cueball describes his reaction and disappointment about the event, describing the event as "a loss for humanity." Cueball is then reminded of his first kiss, which occurred inside of a JCPenney , where a picture of the Mona Lisa hung on one of its walls. He adds this to his comment, explaining that this is why the news hits him hard. However, his story has almost no relation to the Mona Lisa , other than that the picture was at the scene as well as being unnecessary. After posting the comment, Cueball reflects on this and mentions that not every news story is, or needs to be, about himself. The title text describes an exception to this, where his experience IS directly related to the affected painting, as his ex seemingly planned to get revenge on the painting itself. The title text suggests that the dogs destroyed the painting before Cueball's ex could do so. (But perhaps it could be that she let the dogs in, and so this extra information could lead to the police finding the person who was responsible.) [Cueball is sitting at a desk, typing on his laptop. What he types is shown above Cueball, as indicated by the line going from his hands to the text.] Cueball: Devastated to hear that a pack of wild dogs got into the Louvre and shredded the Mona Lisa. Cueball: What a loss for humanity. Cueball: My first kiss was in the aisle of a J.C. Penny [ sic ] that had a poster of the Mona Lisa on the wall, so this is hitting me especially hard. [Caption below the panel] Sometimes I have to remind myself not to make every news story about me.

Projecting

Projecting

https://www.xkcd.com/2506

https://www.explainxkcd.com/wiki/index.php/2506:_Projecting

[Ponytail, Cueball, Megan, and White Hat are standing. Cueball is talking, with arms outstretched, palms up, while the other three are looking at him.] Cueball: Like a lot of you, I have a real problem with projection.

In this comic, Cueball expresses his difficulty with psychological projection . Projection is taking qualities of the self and attributing these qualities to others. Cueball actually admits he has a real problem with projecting, but while doing so, he is seemingly oblivious to the fact, that he is stating this in a way that projects his self-identified difficulty upon his friends: Ponytail , Megan and White Hat . Of course, this could also just be a joke made by Cueball, as it is the joke in the comic. On the other hand, Cueball and Randall have serious issues with social interactions , and this could just be another example of such a problem. In the title text, Cueball continues his projections, stating that this is something we all need to work on . So he continues to believe that all the others have the same problem, not just a lot of them as in his original statement, which left the possibility that not all of them had this issue. In the end, he also tops it by saying but especially you all indicating that he imagines his own case is a less serious issue of projection than that he actually projects the others as having. Alternately, the phrase having a real problem with projection usually means the person speaks quietly, their voice doesn't carry very far, particularly in acting and public speaking environments. Someone with difficulty projecting wouldn't be heard by people in the back row, or perhaps even halfway into the audience (depending how much difficulty they have). This comic is notably smaller than the average xkcd comic, making it the visual / comic equivalent to not projecting. Just as a non-projecting voice cannot be heard very far away, this comic cannot be seen very far away (in either case, not as far as usual). Under this interpretation, the title text is referencing that his audience is also not projecting, they're just as small as he is. Alternatively, Cueball expresses his difficulty with complex numbers . There exists a common projection between the complex and reals, but it may not be clear to him about which method to use or how to do it. If he is projecting onto the real part of the complex line, then his issue is a many-to-one problem, which explains why it is everyone else's problem as well. An alternative perspective might be that the characters, as stick figures, are represented as two dimensional projections of three dimensional objects, and this projection has an issue that depth information is not preserved, so for example, it isn't clear whether cueball is facing towards us or away from us. As his arms are not foreshortened by the projection, this indicates that he is standing in an unnatural pose, so the fact that he says that especially the other characters have a problem with projection would be a good example of psychological projection. A further alternative read could be that Cueball is acting as the Randall surrogate, noting that the other characters are projections of Randall's conscious and subconscious self. The title text could then be read as either directed to those aspects as expressed as characters within the comic, or directed to the reader, who also has things to work on. A different meaning of the term "Projecting" is seen in the fields of public speaking and drama, being the way that a person clearly uses their voice to address an audience. If Cueball is not projecting well, then the characters listening to him may ignore him. Projection is an ongoing issue. People from disparate communities can experience this all the time, where one person assumes out of habit that the other person has the traits of their community. On the end of the spectrum, projection can be completely delusional, as the comic hints at. It would make sense for that be more common for people who attend less to where others are at, such as introverted or powerful people, two groups that experienced engineers can land in. It is also possible that Cueball is addressing the portion of readers who feel the need to project onto Randall their own desire (and meticulousness in analytical searching) for layers upon layers of hidden meaning in xkcd comics. The assumption that he has stuffed several different obscure punchlines into the one sentence of a single-panel comic is, despite the layered punchlines in some other comics, quite a stretch. Randall may be suggesting that such projections from readers onto him are problematic because they cause comic explanation pages to be filled with rambling speculation that can make the explanation of the actual joke harder to understand. [Ponytail, Cueball, Megan, and White Hat are standing. Cueball is talking, with arms outstretched, palms up, while the other three are looking at him.] Cueball: Like a lot of you, I have a real problem with projection.

USV-C

USV-C

https://www.xkcd.com/2507

https://www.explainxkcd.com/wiki/index.php/2507:_USV-C

[A cable with a curled wire displays the end of both of its connectors. The top end has a USB-C connector and the bottom end has a UV-C LED. The UV light is shown coming out of this end with a hazy blue circle around a white middle. The lamp is also bluish. Above is a title and below is a label.] Cursed Connectors #280 USB-C to UV-C

This is the fourth installment in the series of Cursed Connectors and presents Cursed Connectors #280: USB-C to UV-C. It follows 2503: Memo Spike Connector (#102) and was first followed just a bit more than half a year later by 2589: Outlet Denier (#78). This comic depicts a cable that converts from USB-C (at the top of the picture) to UV-C (at the bottom). USB-C is a rotationally symmetrical Universal Serial Bus (USB) connector. UV-C is a range of ultraviolet light with wavelengths between 100 and 280 nm. This is often used as a germicide, so this comic may also be related to the COVID-19 pandemic. The U.S. Food and Drug Administration (FDA) has an infosheet with information about these devices and COVID-19. And the connector number (280) is likely chosen because it is the boundary between UV-C and UV-B in nanometres. Similar cables actually exist, with a USB port at one end to power a small (usually visible light) lamp at the other. A cable with a UV-C lamp could, as noted above, be useful for disinfecting surfaces; however, the depicted design would be problematic because it would expose the user's skin and eyes to harmful ultraviolet radiation. Unless there is more to the UV-C end than indicated, the cable seems not to have use in bidirectional communication (even to confirm that it is plugged in or shone upon some suitable optical transceiver) so in any data transfer situation it could be a limited-range broadcast-only system at best - which has its uses in certain niche cases. The title text mentions that the UV-C is unpolarized . This is a pun with two uses of the term polarized. When referring to a connector 'polarization', or absence of it, it means that USB-C does not force you to use a single correct orientation when using it, i.e. you don't have to turn it "right-side-up" like USB-A or USB-micro. It also refers to the use of a polarizing filter which takes unpolarized light waves and blocks out the waves that are not oriented in the same direction. These are used in sunglasses and photography to eliminate glare and enhance the image. These filters do need to be oriented in a specific direction in order to have the desired effect of passing/blocking a given polarization, perhaps to separate two perpendicularly orientated 'channels' that need to be unmixed exactly knowing the respective orientation of the two signals ( or exactly 180° out, which is what USB-C effectively allows for at present). The light could also have been circularly polarized , which allows 'left' and 'right' rotating polarizations to simultaneously carry separate signals, but not require the same strict orientation to operate properly, at all, so long as arbitrary mirrors are not involved at any stage of the optical path. Regardless, the implication here is that there is no deliberate rationalization of the light to contend with, anyway, which seems to be just making a positive point out of a potentially lost opportunity to double any intended signal bandwidth. The name "Ultra-Serial Violet..." could be read as consciously eschewing all attempts at parallelism, including talkback. [A cable with a curled wire displays the end of both of its connectors. The top end has a USB-C connector and the bottom end has a UV-C LED. The UV light is shown coming out of this end with a hazy blue circle around a white middle. The lamp is also bluish. Above is a title and below is a label.] Cursed Connectors #280 USB-C to UV-C

Circumappendiceal Somectomy

Circumappendiceal Somectomy

https://www.xkcd.com/2508

https://www.explainxkcd.com/wiki/index.php/2508:_Circumappendiceal_Somectomy

[Cueball is sitting with legs out over the edge of an examination table, hugging his stomach, likely because of stomach pains. A doctor in lab coat and a surgical head cap is standing next to the table speaking to Cueball, one arm stretched out towards him.] Doctor: Normally we would remove your appendix from your body. Doctor: But thanks to new surgical techniques, we're now able to remove your entire body from around your appendix!

In normal medicine, appendectomy is the surgical removal of an appendix . The purpose of the appendix is not fully understood, believed to be a reservoir for a human's gut microbiome. However if an appendix is swelling, it comes with risk of bursting and causing massive damage through internal bleeding and septic bacterial infection. In such cases the appendix may be partially removed through surgery. Breaking down the comic's title: circum- means "around," -appendiceal means "the appendix," som(a)- means "the body," and -ectomy means "removal." Therefore, a circumappendiceal somectomy would be "a removal of the body from around the appendix." This appears to be the procedure that the doctor in the comic is describing. The joke is that such a procedure is functionally identical to a typical appendectomy, the removal of the appendix from the body - just viewed from a different perspective. It humorously implies that the entire body of the patient is the problematic part to be removed, leaving the appendix behind. It should be noted, though, that the procedure is identical only if it's done without disrupting the integrity of the body. There are situations in which an essential part is removed from a damaged or unimportant system by dismantling the system, piece by piece, leaving the part behind. Obviously, this would not be an advisable method for treating appendicitis . [ citation needed ] The title text provides personal insight into the comic. It appears Randall has gotten appendicitis before, which may have been the inspiration of 2147: Appendicitis and was treated using antibiotics instead of surgery. However, his appendix became inflamed again, and this time it was removed. Randall's experience is not uncommon, as a 2020 study found that nearly 40% of patients treated with antibiotics for appendicitis required an appendectomy for recurrent appendicitis within 7 years. However, this should be the final time, as it is unlikely to get appendicitis without an appendix. [ citation needed ] However, he does not rule out the possibility that something "extremely unexpected" happened during the surgery which could cause him to suffer from appendicitis again. Possible candidates for such an extremely unexpected event could include the surgeon faking the removal of Randall's appendix and leaving it intact, or removing only part of it, removing Randall's appendix but transplanting someone else's appendix into him instead, or even the appendix's spontaneous regeneration . While most of these possibilities are absurd, stump appendicitis, in which appendicitis occurs in remnant of the appendix that remains after surgery really does occur in 1 in 50,000 cases according to the article Appendicitis after appendicectomy - NCBI . [Cueball is sitting with legs out over the edge of an examination table, hugging his stomach, likely because of stomach pains. A doctor in lab coat and a surgical head cap is standing next to the table speaking to Cueball, one arm stretched out towards him.] Doctor: Normally we would remove your appendix from your body. Doctor: But thanks to new surgical techniques, we're now able to remove your entire body from around your appendix!

Useful Geometry Formulas

Useful Geometry Formulas

https://www.xkcd.com/2509

https://www.explainxkcd.com/wiki/index.php/2509:_Useful_Geometry_Formulas

[Four figures in two rows of two, each being a common two-dimensional representation of a three-dimensional object, with solid lines in front and dotted lines behind. Each figure has some labeled dimensions represented with arrows and a formula underneath indicating its area. Above the four figures is a header:] Useful geometry formulas [Top left; A circle with an inscribed concentric ellipse sharing its horizontal diameter. The edge of the ellipse above the major axis is drawn with a dotted line, while the lower edge is drawn with a solid line, similar to textbook depictions of a 3D sphere. The shared radius/semi-major axis to the right of the center is drawn as an arrow and labeled 'r'. ] A = πr² [Top right; An ellipse with horizontal major axis, plus two straight lines: one from each end of the major axis, up to a point vertical to the center of the ellipse, so that the major axis of the ellipse (not drawn) and the two lines would form an isosceles triangle with a vertical axis of symmetry. The upper edge of the ellipse above the major axis is drawn with a dotted line, while the lower edge is drawn with a solid line, similar to textbook depictions of a right elliptical cone, or more commonly a right circular cone. The semi-minor axis of the ellipse is drawn with an arrow down from the center and labeled 'a' and the semi-major axis is similarly drawn to the right of the center and labeled 'b'. To the right of the shape, the height of the isosceles triangle is drawn using arrows, and labeled 'h'.] A = 1/2 πab + bh [Bottom left; Two ellipses of the same dimensions, with major axes horizontal, drawn vertically one above the other, with vertical lines connecting each end of the major axis of the top ellipse to the corresponding points on the bottom ellipse. The upper edge of the bottom ellipse above the major axis is drawn with a dotted line, while the lower edge is drawn with a solid line, similar to textbook depictions of a right elliptical prism or, more commonly, a right cylinder (circular prism). Inside the shape, the major axis of the upper ellipse is drawn as a double-ended arrow and labeled 'd'. The semi-minor axis of the lower ellipse is drawn as an arrow down from the center and labeled 'r'. To the right of the shape, the length of the vertical lines is replicated using arrows and labeled 'h'. ] A = d(πr/2 + h) [Bottom right; Two rectangles of the same vertical and horizontal dimensions, drawn with one offset diagonally to the upper right of the other, with diagonal lines connecting the corresponding vertices, forming a hexagon with opposite sides parallel. The upper right rectangle has its left and bottom sides drawn with dotted lines, and a similar dotted line is used connecting the bottom left corner of the two rectangles, similar to textbook depictions of rhomboid-based right prisms, or more commonly rectangular prisms. Outside the shape, the bottom edge of the lower rectangle is redrawn below the shape with arrows and labeled 'b'. The length of the left edge is similarly redrawn to the left and labeled 'h'. The length of the diagonal line connecting the upper left corners of the two rectangles is similarly redrawn on the top left using arrows and labeled 'd'. The acute angle between the bottom edge of the lower rectangle, and the dotted diagonal connecting the two lower left corners, is labeled 'θ'] A = bh + d(b sinθ + h cosθ)

This comic showcases area formulas for the areas of four two-dimensional geometric shapes which each have extra dotted and/or solid lines making them look like illustrations for 3-dimensional objects. The first, a simple equation for the area of a circle, the second an equation for the area of a triangle with a semi-elliptic base, the third an equation for the area of a rectangle with an elliptical base and top, and the fourth an equation for the area of a hexagon consisting of two opposing right-angled corners and two parallel diagonal lines connecting their sides. In each case, only the area formed by the outline of each shape is calculated. Similar illustrations are commonly found in geometry textbooks, which are used to depict three-dimensional figures on a two-dimensional page. They commonly make use of slanted lines to indicate edges receding into the distance and dashed lines to indicate an edge occluded by nearer parts of the solid. The joke is that the formulae given here are for the area of each two-dimensional shape within its outer solid lines, not for the surface area or volume of the illustrated 3D object (as would be shown in the geometry textbook). The title text continues the joke by claiming that the dotted lines are simply decorative. The illustrations depict the following plane or solid figures, depending on the interpretation. Top Left - Circle with an inscribed ellipse, or Sphere This illustration is commonly used to depict a three-dimensional sphere, with the ellipse representing a "horizontal" or axial cross-section through the center; the solid lower half of the ellipse represents the "front" of the circumference of this cross-section, while the dotted upper half represents the "back" of the same section, which would be occluded from view if this were a solid shape. The radius of the circle, from the center to the right edge where it meets the ellipse, is labeled 'r'. In a textbook diagram of a sphere, the radius might be instead labeled with a diagonal line from the center to a different point on the ellipse, implying the generality that all points on that cross-section, and indeed on the whole spherical surface, are at the same radius from the center. However, this line would be shorter on the page than the actual radius, making it useless for the formula of the area of the 2D outer shape. The area of the 2D shape on the page is the area of the circle, which is A = πr 2 . This is captioned below the figure. Coincidentally the area of the horizontal cross-section of the 3D sphere, as depicted by the ellipse, is also πr 2 , and a reader familiar with such diagrams might initially assume that this is what was meant. However, this does not extend to the other figures. The 3D sphere commonly depicted by this drawing would have a volume of 4 / 3 πr 3 and a surface area of 4πr 2 . Top Right - Ellipse with symmetrical diagonal lines, or Cone This illustration is commonly used to depict a three-dimensional right circular cone, with the lower half of the ellipse representing the "front edge" of the bottom surface, and the upper half representing the occluded "back edge". However such drawings would usually not use both 'a' and 'b' to describe the radius of the base of the cone, which is drawn as an ellipse due to foreshortening. Alternatively, the drawing could depict a right elliptical cone. Randall approximates the area of the 2D shape on the page as the sum of the area of the triangle formed by the major axis of the ellipse and the two lines, and half of the area of the ellipse ( π / 2 ab) since most of the upper half of the ellipse overlaps the triangle. The equation for this area is A = 1/2 πab + bh. This is captioned below the figure. The actual area of a picture of a cone is not Randall's approximation, because the sides connect at the points on the ellipse where they can spread widest and form tangents to the ellipse, and such points are a little higher than those which define the major axis. This is most obvious in cases when h is only a little larger than a. The area can be computed to be exactly A = b (a arccos(-a/h)) + √(h 2 -a 2 )). The 3D right circular cone commonly depicted by this drawing would have a volume of πr 2 h/3 where r=a=b. The area of the "lower" surface would be πr 2 , while the surface area of the upper conical surface would be πr√(h 2 + r 2 ). Neither of these areas can correspond with the caption in the comic, nor does the total surface area (the sum of these two). If we do not assume that a = b, this drawing could also depict a right elliptic cone. The volume of the elliptic cone would be π / 3 abh. The area of the lower surface would be πab and the area of the curved upper surface would be 2a√(b 2 + h 2 ) 0 ∫ 1 √( a²h²(t²-1) - b²(a²+h²t²) / a²(t²-1)(b²+h²) ) dt. Bottom Left - Two ellipses joined vertically, or Cylinder This illustration is commonly used to depict a 3D cylinder or right circular prism. In this case, the upper ellipse represents the "visible" part of the top circular surface, with its "depth" shorter than its "width" due to foreshortening, and the lower part of the lower ellipse represents the "front" edge of the lower surface; the dotted half of the lower ellipse represents the occluded "back" edge of the lower surface. To add to the confusion, the upper ellipse has its major axis labeled 'd' which usually denotes the diameter of a circular surface, while the lower ellipse has its semimajor axis labeled 'r' which similarly denotes a radius, even though the ellipses drawn have neither diameter nor radius. The 'h' denoting height is also used for both rectangles and solid objects. While 'd' in this case is required for the area calculation of the 2D shape, in textbooks only 'r' may be marked and the arrow may be offset at a diagonal rather than in line with any figurative axis, to imply its applicability to any angle of radius. The non-overlapping parts of the 2D shape are composed of the rectangle formed by the major axes of the two ellipses and the vertical lines, plus half of the top ellipse and half of the bottom ellipse. The area of the rectangle is dh, and the area of an ellipse with semimajor axis d/2 and semiminor axis r is πrd/2. The total area is A = d(πr/2 + h), which is captioned below the figure. A 3D right circular prism (cylinder) would have a volume of πr 2 h and a surface area of 2πr 2 + πdh, or 2πr(r + h) since in this case d = 2r. The area of each flat surface would be πr 2 . If we do not assume d = 2r, then the lateral surface area of the right elliptic cylinder is 4h 0 ∫ 1 √( 1 - t²(1-4r²/d²) / 1 - t² ) dt. The volume is π / 2 rdh. Bottom Right - Parallel Hexagon, or Prism This illustration is commonly used to depict a rectangular prism, with 'b' denoting the 'breadth', 'd' the 'depth' and 'h' the 'height'. However, the labeled angle θ, which is necessary for the area calculation of the 2D shape, would not normally be used in a diagram of a rectangular prism, as all angles are assumed to be right angles. A rhomboidal prism could be accurately described by this diagram with the assumption that the 'base' parallelogram is perpendicular to the 'front' and that the only non-right angle is θ. In that case 'd' would not accurately describe the depth of the solid, which would be d sin θ. The area of the 2D shape is comprised of the rectangle at the lower left, the parallelogram above it, and the parallelogram on the right. The area of the rectangle representing the front face of the prism is bh. The area of the upper parallelogram is db sin θ. The area of the right parallelogram is dh cos θ. The equation for this area is A = bh + d(b sinθ + h cosθ) as is given below the figure. The surface area of the prism would be 2bh + 2db sin θ + 2dh. The volume is bdh sin θ. Assuming a 3D shape, θ can be artificially altered by the projection; the assumption could be made that θ is 90 degrees, and sin θ is 1 (and therefore can be eliminated from the formulas), but since θ is marked, such an assumption might not be valid. In the history of the development of computer-generated 3D graphics, calculations of the apparent visual area taken up by the projection of a volume may have been useful in occlusion-like optimizations, where each drawn pixel may be passed through many fragment shaders. [Four figures in two rows of two, each being a common two-dimensional representation of a three-dimensional object, with solid lines in front and dotted lines behind. Each figure has some labeled dimensions represented with arrows and a formula underneath indicating its area. Above the four figures is a header:] Useful geometry formulas [Top left; A circle with an inscribed concentric ellipse sharing its horizontal diameter. The edge of the ellipse above the major axis is drawn with a dotted line, while the lower edge is drawn with a solid line, similar to textbook depictions of a 3D sphere. The shared radius/semi-major axis to the right of the center is drawn as an arrow and labeled 'r'. ] A = πr² [Top right; An ellipse with horizontal major axis, plus two straight lines: one from each end of the major axis, up to a point vertical to the center of the ellipse, so that the major axis of the ellipse (not drawn) and the two lines would form an isosceles triangle with a vertical axis of symmetry. The upper edge of the ellipse above the major axis is drawn with a dotted line, while the lower edge is drawn with a solid line, similar to textbook depictions of a right elliptical cone, or more commonly a right circular cone. The semi-minor axis of the ellipse is drawn with an arrow down from the center and labeled 'a' and the semi-major axis is similarly drawn to the right of the center and labeled 'b'. To the right of the shape, the height of the isosceles triangle is drawn using arrows, and labeled 'h'.] A = 1/2 πab + bh [Bottom left; Two ellipses of the same dimensions, with major axes horizontal, drawn vertically one above the other, with vertical lines connecting each end of the major axis of the top ellipse to the corresponding points on the bottom ellipse. The upper edge of the bottom ellipse above the major axis is drawn with a dotted line, while the lower edge is drawn with a solid line, similar to textbook depictions of a right elliptical prism or, more commonly, a right cylinder (circular prism). Inside the shape, the major axis of the upper ellipse is drawn as a double-ended arrow and labeled 'd'. The semi-minor axis of the lower ellipse is drawn as an arrow down from the center and labeled 'r'. To the right of the shape, the length of the vertical lines is replicated using arrows and labeled 'h'. ] A = d(πr/2 + h) [Bottom right; Two rectangles of the same vertical and horizontal dimensions, drawn with one offset diagonally to the upper right of the other, with diagonal lines connecting the corresponding vertices, forming a hexagon with opposite sides parallel. The upper right rectangle has its left and bottom sides drawn with dotted lines, and a similar dotted line is used connecting the bottom left corner of the two rectangles, similar to textbook depictions of rhomboid-based right prisms, or more commonly rectangular prisms. Outside the shape, the bottom edge of the lower rectangle is redrawn below the shape with arrows and labeled 'b'. The length of the left edge is similarly redrawn to the left and labeled 'h'. The length of the diagonal line connecting the upper left corners of the two rectangles is similarly redrawn on the top left using arrows and labeled 'd'. The acute angle between the bottom edge of the lower rectangle, and the dotted diagonal connecting the two lower left corners, is labeled 'θ'] A = bh + d(b sinθ + h cosθ)

Modern Tools

Modern Tools

https://www.xkcd.com/2510

https://www.explainxkcd.com/wiki/index.php/2510:_Modern_Tools

[Cueball is sitting on an office chair at his desk typing on his laptop. White Hat is standing behind the desk looking at Cueball.] Cueball: Okay, I've got this neural net generating mostly valid makefiles. Cueball: Next I'm going to train it to distinguish between Bash and Zsh... [Caption below the panel:] People often use ancient tools and UIs to develop modern cutting-edge technology, but I do it the other way around.

Cueball tells White Hat how he has trained a neural net to generate mostly valid Makefiles . This is the file type that Make searches for. In software development, Make is a build automation tool that automatically builds executable programs and libraries from source code by reading files called Makefiles which specify how to derive the target program. (See 2173: Trained a Neural Net ). Make is a very old tool, having first appeared in 1976. Then Cueball continues to tell that he next will train it to distinguish between Bash and Zsh. Bash and Zsh are two command line interfaces for Unix-like OSes. The way to execute commands is almost identical, making detecting a script that contains a mixed syntax nearly impossible. This was previously referenced in 1678: Recent Searches . Bash and Zsh are also old tools, having come out in 1989 and 1990 respectively. A human-designed 'random Makefile'-maker might have been written with this explicit choice amongst the earlier decisions in the generation process, but an AI might be assumed to have started (many, many generations ago) with something close to utter nonsense and painstakingly reached the stage of (mostly!) valid files along the way. Some might say that the differentiation training would have been better added at another point in the lengthy process. On top of that, the current (mostly valid) results may even be polyglot and/or shell-agnostic . Dependant upon the fitness tests in use, many other $SHELL -choices and Makefile styles may have been coevolved as valid (if rarer) subgenus of outputs, such as a command.com -based makefile. In the caption it states that Cueball is using modern tools to make ancient technology, as opposed to other people who use ancient tools and UIs ( User interface ) to develop Modern Tools. In the title text Randall states that he tried to train an AI ( Artificial intelligence ) to repair his horribly broken Python environment . But the AI kept giving up and deleting itself. The joke partly relates to when it or is not appropriate to personify goal-driven processes. In the study of alignment of artificial intelligence, it is common to consider AIs finding ways to meet the tasks they are given that are highly unexpected, and then developing into an apocalypse . A common unexpected solution encountered in research is that the agent finds a way to disable itself as more efficient to meet its reward parameters than anything else it discovers, and then learns to repeatedly do so. The AI might be so intelligent that it had developed critical 'personal' opinions that led it to be so intellectually appalled by the task, or else just found it impossible to fix the python environment and therefore justify its own existence, that it had no other recourse but to commit a form of suicide because Cueball's code was that bad ( which is a recurring theme for Cueball ). Python has been a recurring subject as has Programming and Artificial Intelligence . The main joke is that Cueball is using cutting-edge tools to develop very old technologies, which is perhaps only useful if one is pursuing hobbies in conflict with a differing AI addiction. As the caption implies, it is much more common for people to use fundamental and well-established tools as the toolchain or building blocks of modern technology. A concrete example of this is writing scripts using decades-old Bash to automatically set up a significantly newer (2014) technology called Kubernetes . [Cueball is sitting on an office chair at his desk typing on his laptop. White Hat is standing behind the desk looking at Cueball.] Cueball: Okay, I've got this neural net generating mostly valid makefiles. Cueball: Next I'm going to train it to distinguish between Bash and Zsh... [Caption below the panel:] People often use ancient tools and UIs to develop modern cutting-edge technology, but I do it the other way around.

Recreate the Conditions

Recreate the Conditions

https://www.xkcd.com/2511

https://www.explainxkcd.com/wiki/index.php/2511:_Recreate_the_Conditions

[Megan is standing, pointing a stick at a poster of a particle collision, (as it looks when measured in a particle collider), where many other particles emerge from the central collision, a black spot, with many thin curved lines going away from it, and two larger beams going straight in. Above the upper part of these lines there are three lines of unreadable text, three unreadable labels are written over three of the lines, and there are two unreadable lines of text at the bottom one at each side of the poster.] Megan: Our lab was trying to recreate the conditions that occurred seconds after the Big Bang. [Megan is standing with arms lifted to each side, stick in hand, looking straight out, in an otherwise empty panel.] Megan: But it turns out they were extremely hot and unpleasant. [Megan points at another poster with the stick. The poster shows a picture of a beach, with the sun over the ocean, a palm tree bending in over a parasol stuck in the sand. At the front there is a small table with two drinks on it.] Megan: So now we're trying to recreate the conditions that occurred on this tropical beach in early 2014. Megan: Honestly don't know why we were doing that other thing.

Scientists recreate conditions of things to gain scientific knowledge on a topic to better be able to observe why or how things happen. This could be done by making miniature versions of events and simulating events using safe methods. In this comic, Megan 's lab discovered that the conditions during the seconds after the Big Bang were extremely hot and unpleasant. They have thus decided to attempt to recreate the conditions of a tropical beach in 2014 instead (7 years prior to when this comic was released). Here, the joke is that instead of recreating a condition for scientific study purposes, Megan and her crew were simply trying to create a pleasant environment for recreation, in the sense of personal enjoyment. The title text is a reference to 1949: Fruit Collider a pun of piña colada (Spanish for "strained Pineapple") and a particle collider : the Spanish word "colada" is pronounced similarly to the English word "collider". Taken literally, "piña collider" would be a pineapple collider, which may be interpreted as a fruit juicing machine for making piña coladas. [Megan is standing, pointing a stick at a poster of a particle collision, (as it looks when measured in a particle collider), where many other particles emerge from the central collision, a black spot, with many thin curved lines going away from it, and two larger beams going straight in. Above the upper part of these lines there are three lines of unreadable text, three unreadable labels are written over three of the lines, and there are two unreadable lines of text at the bottom one at each side of the poster.] Megan: Our lab was trying to recreate the conditions that occurred seconds after the Big Bang. [Megan is standing with arms lifted to each side, stick in hand, looking straight out, in an otherwise empty panel.] Megan: But it turns out they were extremely hot and unpleasant. [Megan points at another poster with the stick. The poster shows a picture of a beach, with the sun over the ocean, a palm tree bending in over a parasol stuck in the sand. At the front there is a small table with two drinks on it.] Megan: So now we're trying to recreate the conditions that occurred on this tropical beach in early 2014. Megan: Honestly don't know why we were doing that other thing.

Revelation

Revelation

https://www.xkcd.com/2512

https://www.explainxkcd.com/wiki/index.php/2512:_Revelation

[A Twitter-like page is displayed with a post and a comment nested beneath it. The top poster's profile image is of a man with wild hair, standing on hill near a coast looking out over the ocean. The beach is visible below him. His name is revealed in the comment as John. The poster of the comment's profile image is of a man with flat hair. There is a logo "9 News" at the bottom right. Beneath both pictures are unreadable text. There are also four icons with unreadable text beneath both posts. A line divides the original post and the comment.] John: And I beheld when he had opened the sixth seal, and lo, there was a great earthquake; and the sun became black as sackcloth of hair, and the moon became as blood. Channel 9 News: Hi John, incredible story, hope you and your family are safe. Can Channel 9 News share your account in broadcast and print?

A user with a profile picture of a stick figure with hair, who could be on an island and is called John, posts the Bible text from Revelation 6:12 on a social media website. The author(s) of the book of Revelation refer to themselves as John; some religious scholars identify the author as John of Patmos or as John the Apostle . Thus it is likely that the user has the identity of the said John, either as this biblical-era person themselves (online communities existing in their time, or vice-versa) or adopting the historic character name for interpretive or parodic reasons. The comic places a Biblical event in the modern day to portray what it would be like for apocalyptic miracles to happen nowadays. It also depicts how even the epically largest of our most meaningful and moving moments can end up being treated online. A news channel's official social-media monitor understands this to be an actual (natural) disaster in progress and asks for permission to use the posted information in a broadcast. This could be what would have happened if John had been using Twitter in his own time, in which case his Revelation might have received this response from that time's similarly-connected reporters, perhaps not comprehending the observations to be 'prophetic visions of the future', with potentially a different level of significance altogether, rather than reports of events just happened. If the monitor has just found some form of dislocated account (a very old message, a modern echo for proselytizing purposes or a jape of some kind) then they appear to have been drawn in, having not recognized it as historic text from the Bible. Whichever way, the response is typical of a 'foot in the door' approach probably used for any and all candidate 'breaking news' citizen-reports, identified by trawling and searching the media-feeds for newsworthy content by either reporters or an 'algorithm'. As well as trying to ask for republishing permission, as per the duty of care reporters should grant to their sources, it is couched behind a typically bland statement of concern. The reply may seem underwhelming, given the Revelation-level nature of the scenario, but this early in the reporting cycle the researcher may not have enough facts from which to respond more empathetically. Without any 'empathy' the channel and its staff may look entirely uncaring, but anything too effusive would also look unprofessional. Whether the news-organization and/or its staff could be truly concerned, or simply going through the motions, would highly depend upon their established reputation in the eyes of one viewing this exchange. Cynicism might be involved, all round. The title text modifies verse 14 from "And the heaven departed as a scroll when it is rolled together; and every mountain and island were moved out of their places" to instead reference the infinite scrolling of a news ticker . Thus this news story would just be one on an infinite scroll page of ever-new stories. Alternatively, a Biblical-level disaster actually IS occurring, in which case the newscaster's response is underwhelming, to say the least. Each of the described events happens at times. The sun is black during an eclipse, the moon is red when it sits at the horizon and/or in eclipse, and earthquakes happen on a frequent basis across the planet. When events happen together, it can have great import, and people may become more disconnected from what is real or common nature as lives become digitized. Many people are so used to sunrises and sunsets while seeing the moon high in the sky that they do not realise that the moon also turns red when it rises and sets. In 2014, a series of four total lunar eclipses were identified by some Christian preachers as being the " blood moon " mentioned in Revelation 6:12, but the world did not proceed to end. [ citation needed ] [A Twitter-like page is displayed with a post and a comment nested beneath it. The top poster's profile image is of a man with wild hair, standing on hill near a coast looking out over the ocean. The beach is visible below him. His name is revealed in the comment as John. The poster of the comment's profile image is of a man with flat hair. There is a logo "9 News" at the bottom right. Beneath both pictures are unreadable text. There are also four icons with unreadable text beneath both posts. A line divides the original post and the comment.] John: And I beheld when he had opened the sixth seal, and lo, there was a great earthquake; and the sun became black as sackcloth of hair, and the moon became as blood. Channel 9 News: Hi John, incredible story, hope you and your family are safe. Can Channel 9 News share your account in broadcast and print?

Saturn Hexagon

Saturn Hexagon

https://www.xkcd.com/2513

https://www.explainxkcd.com/wiki/index.php/2513:_Saturn_Hexagon

[Cueball is presenting in front of a poster, which he is pointing at with a stick.] Cueball: We're proud to announce that our team has finally determined the origin and nature of Saturn's polar hexagon. [The poster represents Saturn and its ring-system. There is a massive football/soccer ball drawn as if inside the semi-transparent planet, taking up slightly less than half of it by volume. One of the ball's hexagons coincides with Saturn's polar hexagon, and is labelled "Hexagon". Other labels are illegible. The poster's title is "There's a Big Soccer Ball In There". The rest of the poster is illegible, except for a section heading that reads "BSBIT Model".]

Saturn's Hexagon is a cloud formation on Saturn centered on its north pole. Similar to Jupiter's Great Red Spot , Saturn's Hexagon has proven a persistent feature observed by multiple space probes. The cause was not known until recently, when data from the 2006-2009 Cassini–Huygens probe could be analyzed in depth. This finding was widely publicized in popular science media (see for example [1] ) and is related to how currents flow deep within Saturn's atmosphere. Randall proposes an alternate explanation: it is the top of a soccer ball . Soccer balls are made in the shape of a truncated icosahedron , where faces alternate between regular hexagons and regular pentagons to achieve a more uniform roll. This design was introduced in 1968 as the Adidas Telstar , and is now considered the "traditional" soccer ball. The article is shown to refer to this as the "BSBIT model", a technical-sounding acronym from "Big Soccer Ball In There". "Soccer" is the name used in the United States for association football , a game called simply "football" in much of the world. Similarly, the US makes wide use of customary units of measurement (inches, feet, miles, pounds, etc.) where much of the world uses the SI or metric system (centimetres, metres, kilometres, kilograms, etc.), so "football" is jokingly referred to in the title text as the SI name for "soccer". As much of the Web panders to a significantly US-based audience [ citation needed ] , many sites use only American customary measurements and omit metric equivalents, which might annoy non-US users; Randall parodies this by sarcastically and non-seriously apologizing. [ citation needed ] . Just as the American customary units derive from British Imperial units , the term "soccer" originated in the UK, originally to distinguish it from rugby football (sometimes "rugger"), before soccer became the most common form of football there. This comic may also reference something often quoted to students decades ago that Saturn would float if there were a large enough pool of water to hold it, often having been stated as "Saturn is a giant beach ball". This refers to the property that Saturn is the planet with the lowest average density . This, of course, is a lot more complicated in reality. Incidentally, the presentation of the truncated-icosahedral 'football', pressing one clear polygonal face up along the upper limit of the planetary sphere, has much in common with the (non-truncated) icosahedron that floats within a Magic 8-Ball , arranged to display just one random triangular face whenever its viewing window is upwards. This may be coincidence, without any obvious attempt to directly reference any of the popular memes relating to this. Randall has previously parodied the magic 8-ball in 1525: Emojic 8 Ball . [Cueball is presenting in front of a poster, which he is pointing at with a stick.] Cueball: We're proud to announce that our team has finally determined the origin and nature of Saturn's polar hexagon. [The poster represents Saturn and its ring-system. There is a massive football/soccer ball drawn as if inside the semi-transparent planet, taking up slightly less than half of it by volume. One of the ball's hexagons coincides with Saturn's polar hexagon, and is labelled "Hexagon". Other labels are illegible. The poster's title is "There's a Big Soccer Ball In There". The rest of the poster is illegible, except for a section heading that reads "BSBIT Model".]

Lab Equipment

Lab Equipment

https://www.xkcd.com/2514

https://www.explainxkcd.com/wiki/index.php/2514:_Lab_Equipment

[Ponytail and Cueball are talking to each other. They are standing between two tables with equipment scattered on them, including lens-stands and eye-protection. Ponytail is pointing away from Cueball towards an unidentified off-panel location.] Ponytail: The spectrometer is over here, the Nd:YAG lasers are over here, Ponytail: and in the corner is a laser that turned out not to be useful for us, but we keep it because it's fun to toast marshmallows with it. [Caption below the panel] Every lab in every field has some piece of equipment like this.

This comic claims that in every science lab, there exists some piece of equipment that sticks around less for being useful, and more because the scientists and technicians just think the device is really cool. The comic presents a laboratory containing equipment for analysis of substances. While giving Cueball a tour of the lab equipment, Ponytail shows a spectrometer — a device that examines light emitted from or passed through samples to fingerprint emission or absorption lines in the mix of light. Next she shows the "Nd:YAG" lasers. It is unknown if the multiple lasers are for redundancy or if they have different specifications and are for different tests. "Nd:YAG" stands for neodymium-doped yttrium aluminum garnet ; it is a lasing medium commonly used in lasers. Lastly she shows off a decommissioned laser not used in experiments, but rather for toasting marshmallows. The claim that such things are almost universal is, in fact, very realistic. When doing any research, especially cutting-edge research, it's often difficult to predict what equipment will be useful or not, so it's inevitable those some things will be purchased, and not turn out to be very effective in their experiments. Some of these things will end up being sold, put into storage, repurposed, or even thrown away, but some equipment is enjoyed by the researchers, despite a lack of official uses, and so will end up being kept around. Researchers, being human [ citation needed ] , are going to do some things in the lab for their own amusement, rather than because it's part of a formal experiment, and if equipment has already been purchased, keeping it because it's enjoyable is usually overlooked. Additionally, just playing around with high-end equipment can occasionally lead to useful discoveries. Basic research is difficult to plan out, and sometimes just letting scientists play around with powerful equipment can produce unexpected results, which can lead to new scientific understanding. The title-text mentions that she's using "annealing techniques" to make the perfect s'more. A s'more is a popular treat in the United States and Canada, consisting of one or more toasted marshmallows and a layer of chocolate sandwiched between two pieces of graham cracker. Annealing is more commonly a heat-treatment technique used to influence the nature of the crystals in metals for structural reasons. This is done when jewelry is molded from molten metal, but more likely Randall means a use of annealing in scientific research. Annealing is also used in glass production . This suggests that Ponytail is trying to use lasers and/or other specialized heating equipment to control the melting process of the chocolate, in conjuction with precision toasted marshmallows, to perfect this treat. She points out that this shouldn't be mentioned on the grant application. When labs apply for grants to purchase or upgrade equipment, or to fund research projects, they emphasize the scientific principles that could be advanced (and potential useful products that might be produced) as a result of their research. The idea that researchers might be using the equipment to amuse themselves and work on whimsical side projects would be unlikely to impress the groups offering the grant, [ citation needed ] even though, as Randall points out, such things are pretty much ubiquitous. [Ponytail and Cueball are talking to each other. They are standing between two tables with equipment scattered on them, including lens-stands and eye-protection. Ponytail is pointing away from Cueball towards an unidentified off-panel location.] Ponytail: The spectrometer is over here, the Nd:YAG lasers are over here, Ponytail: and in the corner is a laser that turned out not to be useful for us, but we keep it because it's fun to toast marshmallows with it. [Caption below the panel] Every lab in every field has some piece of equipment like this.

Vaccine Research

Vaccine Research

https://www.xkcd.com/2515

https://www.explainxkcd.com/wiki/index.php/2515:_Vaccine_Research

[White Hat is talking to Cueball.] White Hat: I've been hearing about vaccines. White Hat: But I decided to do my own research. [In a frame-less panel White Hat continues to talk to Cueball.] White Hat: So I spent months on the Internet reading hundreds of studies. [Close up of White Hat as he speaks to Cueball, who replies from off-panel.] White Hat: And wow, I gotta say, White Hat: these vaccines are pretty good. Cueball (off-panel): Oh, really. [Zoomed back out, to White Hat and Cueball talking.] White Hat: Yeah, seems like it'd be great if lots of people got them. White Hat: Is anyone working on that? Cueball: There's been some effort. White Hat: Okay, cool.

This comic is another entry in a series of comics related to the COVID-19 pandemic , specifically regarding the COVID-19 vaccine . The comic starts with White Hat using a common conversational tactic used by vaccine skeptics, and conspiracy theorists, in order to try to persuade others, typically claiming that they did their own research. The phrase "done my own research" is often taken to mean that the speaker is skeptical of the topic, and has done only cursory fact-checking, typically consulting only nonscientific sources that confirm and validate their prior beliefs. However, subverting expectations, it seems that White Hat genuinely had researched the subject deeply, consulting a large number of primary sources, and coming to a conclusion matching the overwhelming scientific consensus that vaccination against COVID-19 is safe and effective. The conclusion he expresses is humorously simple, but entirely in keeping with every expert analysis: "These vaccines are pretty good... Seems like it would be great if lots of people got them." In the last panel, White Hat asks if there are any efforts to distribute the vaccine, to which Cueball responds with understated irony. Anyone genuinely informed about the vaccines would have to be aware of the huge scale of vaccine rollout efforts, or of the resistance to them. It strains credulity that someone could read "hundreds of studies" on the topic and not be aware of how many people had been vaccinated. Cueball, however, doesn't mock White Hat's incongruous ignorance, but simply responds that there's been "some effort", which satisfies White Hat. At the time this strip was posted, only about 42.3% of the world population had been vaccinated against COVID-19. In low income countries, however, distribution has been negligible, and the rate is below 1.9% . In the title text, Randall comments that he feels a little sheepish that he has spent way too much time and effort confirming the statement "yes, the vaccine helps protect people from getting sick and dying". This has been known for a long time despite the anti-vaxxers' efforts. But, as he states, this could be seen as a hobby . Anti-vaxxers often refer to people who get vaccinated as "sheep". This comic may be a sort of spiritual successor to 2281: Coronavirus Research . [White Hat is talking to Cueball.] White Hat: I've been hearing about vaccines. White Hat: But I decided to do my own research. [In a frame-less panel White Hat continues to talk to Cueball.] White Hat: So I spent months on the Internet reading hundreds of studies. [Close up of White Hat as he speaks to Cueball, who replies from off-panel.] White Hat: And wow, I gotta say, White Hat: these vaccines are pretty good. Cueball (off-panel): Oh, really. [Zoomed back out, to White Hat and Cueball talking.] White Hat: Yeah, seems like it'd be great if lots of people got them. White Hat: Is anyone working on that? Cueball: There's been some effort. White Hat: Okay, cool.

Hubble Tension

Hubble Tension

https://www.xkcd.com/2516

https://www.explainxkcd.com/wiki/index.php/2516:_Hubble_Tension

[Cueball and Ponytail are walking to the right. Ponytail has her palm raised.] Ponytail: There are three main estimates of the universe's expansion rate and they all disagree. [They keeping walking to the right.] Ponytail: Measurements of star distances suggest the universe is expanding at 73 km/s/megaparsec. [They are still walking to the right.] Ponytail: Measurements of the cosmic microwave background suggest it's expanding at 68 km/s/megaparsec. [They continue walking to the right. Ponytail points towards Dave who replies from off-panel to the right.] Ponytail: And Dave, who has a radar gun, says it's expanding at 85 mph in all directions. Dave (off-panel): Those galaxies are really booking it! Ponytail: Thanks, Dave.

Ponytail is telling Cueball about the expansion of the universe telling him that there are three main estimates of the rate of expansion, and that they all disagree. She then tells him of the two well known (and very complicated) methods, and finally the joke is that the third method is performed by a guy named Dave (who replies from off-panel), and he claims to measure the speeds with a radar gun, as if the galaxies were speeding here on Earth. The fact that most galaxies are receding from us, and that the distance to the galaxy is directly proportional to the speed (as measured by red-shift ) was discovered in the 1920s by Edwin Hubble and others. This constant of proportionality is known as the Hubble Constant . One way of measuring the Hubble Constant is to measure the distance to (relatively) nearby galaxies. Once distance is obtained, speed can be easily obtained by measuring the red-shift and thus the Hubble Constant calculated. Measuring the distance turns out to be fiendishly difficult because a distant bright star looks the same as a dim star that is closer, and localized movements can influence the speed of recession — though less significantly, for multiple reasons, the further away are the objects that you study. In practice, astronomers have a number of ways of measuring distance that work at different scales, and they can be built upon to measure distance to far away galaxies. This is known as the Cosmic distance ladder . The first rung is parallax . As the Earth orbits around the Sun, nearby stars appear to move slightly relative to distant stars; a star that moves by one second of arc is said to have a distance of 1 Parsec — about 3¼ light years or 30 trillion (3x10 13 ) kilometers. The next rung is Cepheid variables , which periodically brighten and dim. The frequency of variation is related to the absolute brightness of the star, and thus by comparing the absolute to the relative brightness (subject to the Inverse-square law where not otherwise obscured) the distance can be measured. The final rung is Type Ia supernova , which occur when an accreting white dwarf exceeds 1.4 solar masses. Because the initial mass is always identical, the absolute brightness of the explosion is as well, so the distance can be similarly calculated. Putting these together, the best measurement of the Hubble Constant is 73 km/s/Mparsec. This is in conflict with the other main way of measuring the Hubble Constant, analyzing makeup of the Cosmic Microwave Background (CMB) radiation, which yields a value of 68 km/s/Mparsec. The difference is statistically significant, and well outside the error bounds of each measurement. Since the CMB technique relies on our understanding and assumptions about the early universe, as well as on the cosmological effects of General Relativity on large scales, if this discrepancy proved real it could be the gateway to new discoveries in cosmology and gravity, as well as possibly shed light on the origin of the universe and a ' Theory Of Everything '. Cosmologists got quite excited about this. It might also be that there was a previously unaccounted-for error in any of the rungs of the cosmological distance ladder and, once that is fixed, the two results will be consistent. The third method introduced in this comic is a guy named Dave who is trying to use a radar speed gun (as used by the police for detecting speeding cars) to try to measure the movement of astronomical bodies. A radar system works by sending electromagnetic radiation from the gun and then measuring the returned radiation to determine how far away or how fast a moderately distant object is moving. Because of the transmission and return times required (and the inverse-square law), a radar device will only be able to get information about the very closest objects, such as the Moon (a type of Moon bounce ) and other objects orbiting the Earth (or perhaps the Sun), where the influence of being in orbit utterly dominates over any possible Hubble-shift. Doing that still needs very powerful radar systems like the former Arecibo Telescope to be able to get any useful information from that far away; a hand-held radar gun would not be able to 'lock on' across those distances, let alone distant galaxies. Going by back-calculating grossly 'idealized' universe models, as suggested by the other two estimates, a receding velocity of 85 miles per hour ('mph'; about 137 kilometers per hour, 'kph' or 'km/h') should be seen at a distance of roughly 1700-1850 light-years, on the order of the thickness of our galactic disc. Much too far to use a radar gun on, also much too close to exclude any significant galactic stellar motions. Much the same is true if the figure is actually 85 kph (1050-1130 ly), as suggested it might be in the title text. Aside from being practically incorrect, that value of 85 kph relates to around 53 mph, which might be the normally observed traffic speed on certain roads (especially if someone is conspicuously using a radar gun!) if by 'all directions' you effectively mean 'both directions' of traffic flow that Dave could possibly be measuring. Dave may have been referring to the kind of Galaxy that he can more easily find out the velocity of. The comic is likely making fun of the common internet phenomenon of amateur (wannabe?) scientists seeking to discredit established scientific facts by reporting the results of experiments made using everyday tools. Dave has probably heard of the fact that there is no agreement in the scientific measurements of the Hubble constant and decided to try to settle the controversy using the tools at his disposal, without remotely realizing that the margin of error required in the measurements is well outside the range of what can be used with conventional objects. Dave might also lack an understanding of units of measure and dimensions. Ponytail describes the measurements of the rate of universal expansion, a speed that varies with distance, in km/s/Mparsec, having dimension 1/T or 1/time. Dave made his measurements in miles/hour or km/h, which have dimension L/T or length/time. These are not comparable with the official units. Dave does not appear to be aware of this (and Ponytail does not draw Cueball or Dave's attention to it). [Cueball and Ponytail are walking to the right. Ponytail has her palm raised.] Ponytail: There are three main estimates of the universe's expansion rate and they all disagree. [They keeping walking to the right.] Ponytail: Measurements of star distances suggest the universe is expanding at 73 km/s/megaparsec. [They are still walking to the right.] Ponytail: Measurements of the cosmic microwave background suggest it's expanding at 68 km/s/megaparsec. [They continue walking to the right. Ponytail points towards Dave who replies from off-panel to the right.] Ponytail: And Dave, who has a radar gun, says it's expanding at 85 mph in all directions. Dave (off-panel): Those galaxies are really booking it! Ponytail: Thanks, Dave.

Rover Replies

Rover Replies

https://www.xkcd.com/2517

https://www.explainxkcd.com/wiki/index.php/2517:_Rover_Replies

[A post of a rocky landscape and a close-up of a rock is next to a profile picture of the camera of a Mars rover.] Just collected a sample! [Comments below. Each comment has an icon of a person or other image next to it and an illegible name above the comment.] [face of Cueball-like character]: These pictures are great! [curved lines]: I'm so proud of you [Cueball-like stick figure]: Wow you know a lot about rocks [Megan]: Go go go go go! [spiral galaxy-like image]: More propaganda from NASA's 5G vaccine microchip factory [Ponytail]: Quiet, we're not doing that here [unidentified stick figure]: Hello from Missouri (Earth)! [Hairy]: Did you find any skeletons yet [Blondie]: I hope your helicopter comes back! [Caption below frame:] The most unexpectedly wholesome place on the internet is the replies to NASA's rovers on social media.

There is a Twitter account for NASA's Perseverance Mars Rover , which recently collected samples. The Twitter account tweets in the first person like in the comic. Likely a human on earth is playing the role of the rover [ citation needed ] . While the exact post shown does not exist, it has posted a similar tweet. The first four replies (in order of top-to-bottom) are likely just general compliments to the rover, demonstrating that the replies are indeed wholesome. Reply three in particular references rocks, as the main purpose of most Mars rovers is to perform Martian geology. Reply five is a mashup of conspiracy theories, including about 5G communications, vaccines , and others. Ponytail then replies "Quiet, we're not doing that here", implying either that she doesn't want it in the replies to this, that she thinks that the rude reply should be posted somewhere else, that she's a NASA employee stating that NASA does not have a 5G vaccine-microchip factory, or that she also is a conspiracy theorist trying to redirect the fellow commenter to other forums with more susceptible audiences. The next reply references people saying where they're from, then clarifying where that is in brackets, e.g. Wingerworth (England). This commenter expands that to clarify that they are from Earth, joking that the planet may be ambiguous as the Mars rover is not on Earth. In reality, this ambiguity does not exist as humans only live on Earth, [ citation needed ] thus contributing to the humor. The second-to-last reply is likely a misunderstanding, with the commenter believing that the rover is digging to perform anthropology or paleontology, not geology. The commenter could, however, believe that there is/was complex life on Mars, thus allowing the possibility that there are Martian skeletons for the rover to find. The final reply is a reference to Ingenuity , a small helicopter which Perseverance took to Mars as a technology demonstrator . It has been very successful and completed many flights, often taking it quite far from Perseverance. The title text is in the form of another reply. The character posting that reply believes that the rover has taken its phone to Mars, and has used that to take the pictures. This is likely because most photos on social media are taken on phones, and social media sites are often designed for phones. In addition, Perseverance and Curiosity differ from previous rovers in that they have cameras mounted on flexible arms, allowing them to take photographs of themselves - somewhat akin to a smartphone on a selfie-stick. In reality, Mars rovers don't have smartphones, and Perseverance is taking photos with an equipped camera. While this comic is most likely referencing Perseverance, there is another small possibility that Curiosity is shown here, as Curiosity also has collected samples . This is unlikely though due to the timing of this comic. [A post of a rocky landscape and a close-up of a rock is next to a profile picture of the camera of a Mars rover.] Just collected a sample! [Comments below. Each comment has an icon of a person or other image next to it and an illegible name above the comment.] [face of Cueball-like character]: These pictures are great! [curved lines]: I'm so proud of you [Cueball-like stick figure]: Wow you know a lot about rocks [Megan]: Go go go go go! [spiral galaxy-like image]: More propaganda from NASA's 5G vaccine microchip factory [Ponytail]: Quiet, we're not doing that here [unidentified stick figure]: Hello from Missouri (Earth)! [Hairy]: Did you find any skeletons yet [Blondie]: I hope your helicopter comes back! [Caption below frame:] The most unexpectedly wholesome place on the internet is the replies to NASA's rovers on social media.

Lumpers and Splitters

Lumpers and Splitters

https://www.xkcd.com/2518

https://www.explainxkcd.com/wiki/index.php/2518:_Lumpers_and_Splitters

[Megan and Cueball are standing looking at each other. There are boxes beneath each of them with a label.] Megan: Really, we're both just categorization pedants. Label: Lumper Cueball: Ahh, so you're a meta -lumper. Label: Splitter

It is common to separate groups of things — species, people, languages, software models, etc. — into categories , but different people may do this in different ways. "Lumpers" work from the ground up by focusing on similarities among individual things to create larger categories, while "splitters" do the opposite, taking larger categories and trying to find characteristics that are not shared by all members of the group to further divide them into smaller subsets. The comic points out the meta -ness of categorizing people based on how they categorize. It labels Megan and Cueball as those two types of categorizers. Megan, the lumper, describes herself and Cueball as both being "categorization pedants", lumping the two distinct categories "lumpers" and "splitters" into one. Cueball, the splitter, subcategorizes Megan into a more specific type of lumper: a "meta-lumper"—since the things Megan was lumping includes lumpers themselves—thereby splitting off lumpers from meta-lumpers. If Cueball further categorized himself he would be a meta-splitter. The title text references the opening line of the novel Anna Karenina by Leo Tolstoy, which reads (as translated into English), "Happy families are all alike; every unhappy family is unhappy in its own way." Randall is drawing a parallel between this line and the lumper/splitter distinction because the line lumps one group of things (happy families) while splitting another group (unhappy families). Additionally, this may be a reference to the podcast episode "Lingthusiasm Episode 60: That's the kind of episode it's - clitics" [1] , published a few days before the comic, wherein the hosts separate people into lumpers and splitters of clitics. [Megan and Cueball are standing looking at each other. There are boxes beneath each of them with a label.] Megan: Really, we're both just categorization pedants. Label: Lumper Cueball: Ahh, so you're a meta -lumper. Label: Splitter

Sloped Border

Sloped Border

https://www.xkcd.com/2519

https://www.explainxkcd.com/wiki/index.php/2519:_Sloped_Border

[Cueball and Blondie are standing on a podium. They are holding a document together between them, filled with unreadable text. On either side of the podium are two informational graphics each on a stand. They are placed a bit behind the back side of the podium. The graphic to the left shows a cross-sectional view of a non-vertical border, shown as a dotted line going up between Cueball and Blondie, who both are standing on the ground. The angle is indicated and noted, and the line tilts towards Blondie's side. The graphic on the right shows a skewed perspective of a similar setup of the non vertical border, shaded so what is behind it becomes gray. There are also some lines on this plane to indicate where it is. It almost looks like a window, but people can move through it. There are also two more persons than on the left, Megan, who is on the same side of the border as Cueball, and another Cueball-like guy standing next to Blondie. Megan is entirely on Cueball's side of the plane, but the other three are positioned so they are intersected by the 'shaded plane' of the border, with the effect that some or most of their bodies are beyond the sloped boundary, in the gray area, but not all. Cueball and Blondie are postureed in a mutual greeting across this border, as the others look on.] Cueball: With this treaty, we are proud to announce the creation of the world's first sloped international border! Angle: 74° [Caption below frame:] If I'm ever put in charge of a country, I'm going to spend all my time trying to think of new ways to make life a nightmare for GIS people.

Every country has land and sea international borders that demarcate the extent of their territory and their legal jurisdiction. These borders are established through law, treaty, or consensus. Establishing an international border is maintained by present-day customs, immigration, and security checks. Some countries (like Cyprus ) have established a buffer zone outside of their international border in order to gain additional protection during a conflict, and most countries have an offshore Exclusive Economic Zone in order to preserve exclusive proprietorship of marine resources such as oilfields and fishing grounds. In this comic, Cueball and Blondie have established a "sloped" international border through a treaty. Usually borders are perpendicular to the ground [ citation needed ] so that all the air(space) above the ground belongs to the same country. This is called Air sovereignty . Thus it suffices to define the border on the earth surface, as 1D lines across the curved 2D surface. The precise definition is that a line from the center of the Earth through the point of the border is drawn. Sloped terrain is immaterial to the border of the air sovereignty which is still vertical, even if not perpendicular to the terrain. If the borders were sloped (with respect to the horizontal ground level) an airplane would need to know its precise height to decide if another country's jurisdiction currently applies. With the help of the Global Positioning System this would be in principle possible, although the height information of GPS is less reliable. (It might be possible to program a computer to use altitude data from the airplane's altimeter along with latitude and longitude data from the GPS and a relevant ground relief database to make an accurate determination.) Most countries would not agree to a border that cuts into their airspace and shrinks their territory as the altitude increases; most cases of countries losing area have come about as a result of trying to avert, or losing, an armed conflict. It is entirely possible that Cueball's country has compelled Blondie's country to accept its demands, of which the redrawn border is one. Alternatively, Cueball's country may be deliberately reducing its own airspace purely because it will cause problems. There is at least one famous case of a border being affected by elevation: the Franco-Swiss border bisects the staircase of the Hotel Arbez . Hence, although part of the upper floor is geographically in France, the entire floor is Swiss territory, because it is only accessible through Switzerland. The mathematical computation for an angled air sovereignty seems relatively straight-forward at low level and could be expressed with a single line of code or a single equation, although the people acting on the information are likely unfamiliar with code and equations and likely use tools with completely no support for sloped borders. The mention of curvatures in the title text may reveal some emergent problems that need accounting for. A totally straight line drawn far enough upwards at an angle will find the surface of the Earth curving away beneath it (not even considering terrain undulations) and the angle to the local vertical will reduce as it continues, tending towards vertical as you head towards infinite altitude. Alternately (although it seems this is not the case) the profile of the sloped border may be assumed to remain at a constant angle to the shifting vertical, in which case it describes a certain form of spiral (which will eventually loop around the earth). A third option is that it gains altitude at a constant rate, with respect to the passage of land measured on its surface track, to form a different spiral , in which case it will still loop around the Earth but at an angle that increasingly tends towards horizontal. While the comic doesn't mention this, such a boundary should probably also extend underground, in the opposite direction. (The straight-line version, if implemented, will eventually reach a depth at which it is tangential to the radius and then rise back through the surface an equal distance further around the planet.) This would then impact, at practical depths for such things, planning rights for property foundations and, at deeper levels, mining rights for minerals. Practically an upper-limit to a nation's claim (somewhat below satellites, e.g. the Karman Line) and a lower limit (well before reaching the Earth's mantle) will prevent many of these complications, together with intersections with other (probably vertical) 'territorial volume' borders that will supercede in any compound claims to ownership. - However, it is still very important to specify exactly which curve (i.e. with respect to what) the boundary is designed to respecting. "GIS" refers to geographic information system , a set of tools and methods for capturing, analyzing and presenting spatial and geographic data. While altitude is already an (optional) element in the blocks of information, people developing these systems would be inconvenienced by the additional requirements demanded by the border described in the comic. It is possible this comic is inspired by such boundary disputes as the Beaufort Sea 'wedge' which, while in this case perpendicular to the surface, suffers from alternative interpretations of how to extend it from the shoreline out towards international waters. [Cueball and Blondie are standing on a podium. They are holding a document together between them, filled with unreadable text. On either side of the podium are two informational graphics each on a stand. They are placed a bit behind the back side of the podium. The graphic to the left shows a cross-sectional view of a non-vertical border, shown as a dotted line going up between Cueball and Blondie, who both are standing on the ground. The angle is indicated and noted, and the line tilts towards Blondie's side. The graphic on the right shows a skewed perspective of a similar setup of the non vertical border, shaded so what is behind it becomes gray. There are also some lines on this plane to indicate where it is. It almost looks like a window, but people can move through it. There are also two more persons than on the left, Megan, who is on the same side of the border as Cueball, and another Cueball-like guy standing next to Blondie. Megan is entirely on Cueball's side of the plane, but the other three are positioned so they are intersected by the 'shaded plane' of the border, with the effect that some or most of their bodies are beyond the sloped boundary, in the gray area, but not all. Cueball and Blondie are postureed in a mutual greeting across this border, as the others look on.] Cueball: With this treaty, we are proud to announce the creation of the world's first sloped international border! Angle: 74° [Caption below frame:] If I'm ever put in charge of a country, I'm going to spend all my time trying to think of new ways to make life a nightmare for GIS people.

Symbols

Symbols

https://www.xkcd.com/2520

https://www.explainxkcd.com/wiki/index.php/2520:_Symbols

[A list with 14 different scientific constants/symbols are shown. Next to each symbol is a description. Above the list is a heading and beneath that a subheading.] Symbols And what they mean d ⁄ dx An undergrad is working very hard ∂ ⁄ ∂x A grad student is working very hard ħ       Oh wow, this is apparently a quantum thing Rₑ     Someone needs to do a lot of tedious numerical work; hopefully it's not you (T a ⁴ - T b ⁴)    You are at risk of skin burns N A You are probably about to make an incredibly dangerous arithmetic error µm    Careful, that equipment is expensive mK    Careful, that equipment is very expensive nm    Don't shine that in your eye eV Definitely don't shine that in your eye mSv  You're about to get into an internet argument mg/kg      Go wash your hands µg/kg      Go get in the chemical shower π or τ      Whatever answer you get will be wrong by a factor of exactly two

This comic refers to elements of (mostly mathematical or engineering) notation commonly used in various fields of math and science. Each piece of notation is presented as "symbolizing" not what it specifically means, but a typical context in which it might be encountered, see below . Many of the individual descriptions look like verbiage that might be found on informational or warnings signs or placards, although typically with a silly edge. The title text refers to two non-SI units of radiation measurement, röntgen and rem . In the mid-20th century when they were in use, the dangers of radiation weren't as well understood as today, so an area with radiation that was noteworthy back then is probably dangerous , hence the no trespassing part. Later Randall made a similar comic, 2586: Greek Letters , regarding the use of Greek letters in math. d ⁄ dx : An undergrad is working very hard d/dx is the symbol for a single-variable derivative . This is one of the basic operations in calculus and consequently is ubiquitous in the work of undergraduates in the sciences. A hard-working undergraduate in the relevant fields would churn through exercises using this symbol. ∂ ⁄ ∂x : A grad student is working very hard The replacement of the standard "d" letters with the curly letters "∂" denotes the partial derivative, which generalizes the ordinary derivative to multi-variable calculus. Problems with partial derivatives, especially partial differential equations, can be extremely challenging. Although PDEs would typically be first taught at an undergraduate level, difficult partial derivatives would be encountered in graduate-level work. ħ: Oh wow, this is apparently a quantum thing ħ (pronounced "h-bar") is a symbol used for (the reduced) Planck's constant , a universal, fundamental constant in quantum physics. ħ is equal to the energy of a photon divided by its frequency, and angular momentum in quantum mechanical systems is measured in quantized integer or half-integer units of ħ. Classical physics appears as a limit of quantum physics if all "actions" (quantities of dimension energy * time, momentum * length, or angular momentum) are much larger than ħ. Conversely, you can also formally set ħ=0 to get classical results from quantum formulae. This means that effects that are proportional to some power of ħ cannot be explained classically, and instead are "a quantum thing". Rₑ: Someone needs to do a lot of tedious numerical work; hopefully it's not you The Reynolds number (which is usually denoted by "Re," not "R e " as it appears in the comic) is the most important dimensionless group in fluid mechanics. Named for Osborne Reynolds, Re characterizes the relative sizes of inertial and viscous effects in a moving fluid. Large values of Re are indicative of turbulent flow, which cannot usually be retrieved analytically, and so numerical modeling is necessary. Accurate numerical studies of high-Reynolds-number flows are notoriously difficult to create and program. Alternatively, Rₑ could stand for electronic transition dipole moment in a molecule. This appears in quantum-mechanical calculations of transition probabilities and also includes a lot of unpleasant numerical work. Rₑ is also a term used for the radius of the Earth at mean sea level, though this is not necessarily a complex term in and of itself. Another alternative is that Rₑ could refer to Relative Error, a measurement of precision or accuracy. Used often in the analysis of scientific data and numerical analysis. (T a ⁴ - T b ⁴): You are at risk of skin burns The Stefan-Boltzmann law says that a perfectly absorbing ("black body") source emits electromagnetic radiation with a power per unit area of σT 4 , where σ is a known constant and T is the absolute temperature. The quantity (T a 4 – T b 4 ) thus appears in any calculation of purely radiative energy transfer between two bodies, one at temperature T a and the other at T b . When the radiative transfer is large enough to be the most important form of heat interchange, it is normally also large enough to sear the skin with thermal or ultraviolet burns. N A : You are probably about to make an incredibly dangerous arithmetic error N A , or Avogadro's number , is the number of molecules in a mole of a substance, approximately the number of carbon atoms in exactly 12 grams of carbon-12. This is an enormous number, exactly 6.022 140 76 × 10²³, or 602 214 076 000 000 000 000 000. Working with N A , it is easy to accidentally divide by it instead of multiplying or vice versa, leading to erroneous and nonsensical answers such as ~10 -23 molecules (even though you can't have less than 1 whole molecule) or ~10 46 moles (>10 43 to to 10 45 kilograms, depending on the chemical) of a substance. µm: Careful, that equipment is expensive Micrometers are a very small unit of distance. Micrometers are commonly used to measure wavelengths in the infrared, and infrared detectors are very expensive, compared with visible wavelength counterparts. Of course, micrometers are used as a measurement of distance in other contexts, but any distance-measuring device capable of accurately measuring micrometer distances would also be expensive. Similarly, tools used to create or calibrate items within micrometer tolerances can also be expensive. mK: Careful, that equipment is very expensive Kelvin is a temperature scale roughly speaking similar to Celsius, but taking absolute zero as its zero point instead of the freezing point of water (rigorously speaking, its definition is now based on the Boltzmann constant ). Millikelvins (1/1000 of a Kelvin) are used for high precision temperature work. Frequently this is used in processes of cooling temperatures to nearly absolute zero - such as superconductors or other quantum effects that occur when atoms are almost still. This is suggesting that the symbol appears on a sensitive experimental system probing quantum mechanical behavior that would likely only exist in an advanced laboratory. Any equipment that works down at mK temperatures, or at least to mK precision and accuracy, is likely to be very expensive. nm: Don't shine that in your eye Nanometers are frequently seen in the listed wavelengths for lasers. Pointing a visible or infrared laser at someone's eye is notoriously dangerous; the tightly-focused coherent light can cause permanent damage very quickly. eV: Definitely don't shine that in your eye Electron volt energies are typical of moderate-energy particle beams, produced by accelerating electrons (or protons) over macroscopic voltages. These particle beams can be even more damaging (and are probably a direct reference to Anatoli Bugorski) to soft tissues than optical-wavelength lasers. mSv: You're about to get into an Internet argument The millisievert is a unit of radiation dose absorbed. It is a very small dosage, but the joke refers to Internet trolls debating the effects of low-dose radiation sources, such as 5G wireless networks. Randall's comment may also be referring to this chart . mg/kg: Go wash your hands This unit measures the dose of a drug or other chemical in milligrams per kilogram of body mass. If the appropriate dose - or worse, the lethal dose - is measured in mg/kg (parts per million), then the substance may be quite toxic. µg/kg: Go get in the chemical shower A unit 1/1000 times the size of mg/kg. If a dosage is measured in micrograms per kilogram (parts per billion), any accident probably requires whole-body decontamination procedures. π or τ: Whatever answer you get will be wrong by a factor of exactly two π is defined as the ratio of a circle's circumference to its diameter, while τ is defined as the ratio of a circle's circumference to its radius (and is therefore equal to 2π). π has been used as the primary constant for describing the circumference and area of circles millennia ago, but proponents of τ claim that τ is more natural in most contexts since it makes working in radians more straightforward. The joke here is that whichever constant you use, it will probably be the wrong one (off by a factor of two, one way or the other) for the formula you are trying to use. The debate over Tau vs Pi was solved by Randall in this compromise: 1292: Pi vs. Tau . [A list with 14 different scientific constants/symbols are shown. Next to each symbol is a description. Above the list is a heading and beneath that a subheading.] Symbols And what they mean d ⁄ dx An undergrad is working very hard ∂ ⁄ ∂x A grad student is working very hard ħ       Oh wow, this is apparently a quantum thing Rₑ     Someone needs to do a lot of tedious numerical work; hopefully it's not you (T a ⁴ - T b ⁴)    You are at risk of skin burns N A You are probably about to make an incredibly dangerous arithmetic error µm    Careful, that equipment is expensive mK    Careful, that equipment is very expensive nm    Don't shine that in your eye eV Definitely don't shine that in your eye mSv  You're about to get into an internet argument mg/kg      Go wash your hands µg/kg      Go get in the chemical shower π or τ      Whatever answer you get will be wrong by a factor of exactly two

Toothpaste

Toothpaste

https://www.xkcd.com/2521

https://www.explainxkcd.com/wiki/index.php/2521:_Toothpaste

[Cueball, holding his arms out, is talking to Megan.] Cueball: I can't believe she said that. Cueball: She apologized, but you can't put the toothpaste back in the tube. [Megan holds a hand, palm up, out towards Cueball as she replies.] Megan: Sure you can; it's easy. You just put your mouth over the opening. [Finally they stand straight talking.] Cueball: Well, that's the worst thing you've ever said. Megan: Sorry, I can take it back. It's just like- Cueball: No!

Cueball is telling Megan about his friend. He indicates that she said something shocking and probably hurtful. He then states that even though she tried to apologize it was too late, the words had been said and it cannot be taken back. He uses a phrase to underline this: You can't put the toothpaste back in the tube. Putting toothpaste back in its tube is often used as an analogy for something irreversible, such as how you can't undo speaking. Megan, however, rejects this assertion and says that you actually can put toothpaste back in its tube, which is certainly possible in some cases. There are many ways to do this, and none of them are recommendable if the toothpaste has come into contact with something non-sterile. But she chooses a particular nasty one where she would blow the paste in her mouth back into the tube. This is obviously much more unsanitary than simply returning unused toothpaste to the tube, which someone might reasonably want to do after squeezing out more than they wanted. Cueball is so disgusted by this suggestion that he states that Megan's suggestion is the worst thing she has ever said. The joke then comes when Megan assumes that Cueball's original analogy still holds, that taking words back is like putting toothpaste back in to the tube. So therefore she can actually unsay something. She starts to say exactly what Cueball's other friend did "Sorry, I can take it back". But then she says, "It's just like--", and was presumably about to continue, "--putting toothpaste back in the tube" (or perhaps, since it's Megan, was going to give a new analogy that was even worse). However, Cueball forcefully interrupts her, because the idea of putting toothpaste back in the tube now evokes the distasteful mental image of Megan blowing used toothpaste back into the tube. Toothpaste is normally loaded into the tube from the back, before it is crimped shut. However, it should technically be possible to push an extruded amount of paste back in from the front by wrapping one's lips around the whole front of the tube and blowing the paste you have in your mouth back in. This positive pressure can re-inflate the tube the same way one blows up a balloon. However, blowing the toothpaste back into the tube would be highly unsanitary, and as the main purpose of toothpaste is to clean teeth, the end result is both counterproductive and disgusting. [ citation needed ] In some cases paste coming out of a tube will be sucked back in if the pressure is released. Such containers would probably be able to suck toothpaste back in, if it was still lying on the toothbrush in one blob (or on the table/in the sink if dropped). As above mentioned this would be unsanitary as germs etc. could get back inside the tube, where the paste is supposed to be clean. The title text spoofs a common line found in toothpaste commercials: "9 out of 10 dentists recommend using our brand." This statement is very easily manipulated through any number of basic marketing tactics (such as only asking 9 dentists, whom are all paid handsomely), and its ubiquity lends it to spoofing. In this case, it's spoofed by saying that nine out of ten dentists are dis satisfied with Megan's approach (or with Randall and his ideas, as it is usually he who speaks in the title text; if it refers to Randall himself it is reminiscent of all the conferences he has been banned from ) and have banned the toothpaste spitter from their offices. It may actually say more about any dental establishment that does not disapprove of what Megan apparently is not just theorizing about doing - but maybe they are disapproving too, just not considering it bad enough to ban her from office. [Cueball, holding his arms out, is talking to Megan.] Cueball: I can't believe she said that. Cueball: She apologized, but you can't put the toothpaste back in the tube. [Megan holds a hand, palm up, out towards Cueball as she replies.] Megan: Sure you can; it's easy. You just put your mouth over the opening. [Finally they stand straight talking.] Cueball: Well, that's the worst thing you've ever said. Megan: Sorry, I can take it back. It's just like- Cueball: No!

Two-Factor Security Key

Two-Factor Security Key

https://www.xkcd.com/2522

https://www.explainxkcd.com/wiki/index.php/2522:_Two-Factor_Security_Key

[Cueball and Ponytail stand facing each other.] Cueball: I got one of those two-factor security keys you've been bugging me about. Ponytail: Great! [Cueball and Ponytail continue facing each other.] Cueball: It took a lot of work, fiddling with configurations, annoying setbacks, and general pain, [Closeup on Cueball holding a keychain.] Cueball: ... but I finally got it onto the metal ring of my keychain. Ponytail [off-panel]: At least now it's secure. Cueball: Yeah, this thing is not coming off. An authenticaion 'factor' is a distinct method of proving your legitimate use of a service or product. They can be broadly be grouped into three main groups. One-Factor Authentication now may trying to avoid the shortcomings of the Password system (including the intervention of a 'remembered' password) by developing passwordless authentication techniques based upon "have/are" factors only. Two-Factor Authentication was usually the addition of a physical/biometric authentication method to augment each use of a known password/PIN (e.g. the 'rolling token' number). Conversely, the physical authentication of a bank-card has required backing up by its remembered PIN when used in cash-machines/ATMs. (In shops, checking against the signature written on the same card was for a long time the verification of valid ownership, this recently progressed to Chip-And-Pin, but then in many cases has been superceded by Contactless (NFC) versions, making it a Single-Factor solution in sufficiently low-value transactions.) Many people may be more familiar with an occasional Second-Factor Re Authentication, when (for one reason or another) they are no longer able to provide a valid password for some login or other, and activate the "Forgot my password" request which sends a link to their backup email account. Where one is set up, is still active and and you have not also lost the ability to access that. (This is not the situation that Cueball is in, or may be in.) This has largely replaced the infamous "Challenge Question" (though may still be combined with it) probably to defeat replay-attacks or the more clever phishing attacks. Three-Factor Authentication should really be a "know" and "have" and "are" combination. Imagine the cinematic scene of the 'President' granting authority for a nuclear attack by inserting a physical key into the required device, typing in their code and then presenting their eye to a retinal scanner. Anything that is (seriously) quoted as Four-Factor, or above, is going to either duplicate the number of required verifications of a similar scope (towards diminishing returns) or is describing a setup of a number of optional methods from which a lesser number would be considered sufficiently valid to provide. e.g. registering all ten finger/thumb-prints in case of some random future digital injury.

Two factor security authentication (also see #Trivia ) is something that Ponytail has clearly been talking to Cueball about. In this strip, Cueball is telling her that he has finally buckled down and gotten the two factor security key that she has pestered him to get. He recites the trials that he endured in "installing" the key, all of which seem plausible configuration issues for setting up a proper two-factor authentication from scratch. However it is then revealed that all this work was just the task of attaching the 'key' (which looks like it could be a common brand of physical two-factor key fob or dongle) onto his metal keyring. Metal keyrings are reliably secure as far as keeping a key attached, but this is in part because of how notoriously difficult it is to add a key to or remove a key from them. The rings must be forced apart and held apart while the key traverses however many layers the ring has (usually two or three, though keyrings with more layers are not unheard of). Cueball confidently asserts (to off-screen Ponytail, who probably was expecting something more practical) that his key is not coming off, indicating both a (well-founded) faith in the keyring's ability to keep his key, and a desire to not go through the same process in reverse. Presumably all his effort was in "installing" the key onto the keychain, and he probably hasn't actually set it up for any of his accounts, leaving them just as insecure as they were. The title text has a similar double meaning. Cueball would of course use it to the "proof" of his efforts installing the key--though difficult, metal keyrings can be forced apart physically by human hands, at least if the human in question has fingernails sturdy enough to slip between the rings, at which point the insertion of a finger would be enough to keep it apart until the key is inserted. However, keeping the rings apart can be strenuous on the fingers, and can result in bruising, which Cueball is all too familiar with. Proof of work alludes to the cryptographic concept, which ties (sideways, as proof of work is a security term for a concept intended to deter denial of service and similar volume-based attacks but not directly related) back into the two-factor authentication. Additionally a third meaning could be that while he spent a lot of time setting up 2FA he totally overlooked the possibility of him losing his whole keychain thus locking him out of all the services that requires 2FA if he didn't set up yet another layer of backup. [Cueball and Ponytail stand facing each other.] Cueball: I got one of those two-factor security keys you've been bugging me about. Ponytail: Great! [Cueball and Ponytail continue facing each other.] Cueball: It took a lot of work, fiddling with configurations, annoying setbacks, and general pain, [Closeup on Cueball holding a keychain.] Cueball: ... but I finally got it onto the metal ring of my keychain. Ponytail [off-panel]: At least now it's secure. Cueball: Yeah, this thing is not coming off. An authenticaion 'factor' is a distinct method of proving your legitimate use of a service or product. They can be broadly be grouped into three main groups. One-Factor Authentication now may trying to avoid the shortcomings of the Password system (including the intervention of a 'remembered' password) by developing passwordless authentication techniques based upon "have/are" factors only. Two-Factor Authentication was usually the addition of a physical/biometric authentication method to augment each use of a known password/PIN (e.g. the 'rolling token' number). Conversely, the physical authentication of a bank-card has required backing up by its remembered PIN when used in cash-machines/ATMs. (In shops, checking against the signature written on the same card was for a long time the verification of valid ownership, this recently progressed to Chip-And-Pin, but then in many cases has been superceded by Contactless (NFC) versions, making it a Single-Factor solution in sufficiently low-value transactions.) Many people may be more familiar with an occasional Second-Factor Re Authentication, when (for one reason or another) they are no longer able to provide a valid password for some login or other, and activate the "Forgot my password" request which sends a link to their backup email account. Where one is set up, is still active and and you have not also lost the ability to access that. (This is not the situation that Cueball is in, or may be in.) This has largely replaced the infamous "Challenge Question" (though may still be combined with it) probably to defeat replay-attacks or the more clever phishing attacks. Three-Factor Authentication should really be a "know" and "have" and "are" combination. Imagine the cinematic scene of the 'President' granting authority for a nuclear attack by inserting a physical key into the required device, typing in their code and then presenting their eye to a retinal scanner. Anything that is (seriously) quoted as Four-Factor, or above, is going to either duplicate the number of required verifications of a similar scope (towards diminishing returns) or is describing a setup of a number of optional methods from which a lesser number would be considered sufficiently valid to provide. e.g. registering all ten finger/thumb-prints in case of some random future digital injury.

Endangered

Endangered

https://www.xkcd.com/2523

https://www.explainxkcd.com/wiki/index.php/2523:_Endangered

[Ponytail stands facing Cueball and Megan in front of a poster board.] [Ponytail is pointing a stick to the board reading "Current List" with bullet points beneath.] [The first bullet reads Influenza B/Yamagata.] [Four further bullet points follow, which are left indistinct.] Ponytail: Influenza's genetic diversity has declined during the pandemic, and the B/Yamagata lineage is at risk of extinction. Ponytail: Which would be such a shame. Megan: Yeah, I'm sooooooo worried about it. Cueball: We'd be just heartbroken! [Caption below the panel]: When a pathogen that scientists really don't like is close to disappearing, it gets added to the sarcastic endangered species list.

The endangered species list (also known as the IUCN Red List ) is a system for categorizing species based on "level of extinction". This list is primarily focused on macroscopic organisms such as animals and plants, as it is these organisms whose extinction is easiest to quantify, and on which most conservation efforts focus. Generally, it is a serious concern when a species is listed on the endangered species list, as this indicates its extinction could be at hand. Ponytail , Cueball , and Megan in this comic are scientists who maintain an endangered species list of microscopic pathogens. People generally want harmful pathogens and parasites to go extinct, [ citation needed ] unlike harmless plants and animals, so each species added to the pathogen endangered species list is a cause for celebration rather than concern, and the characters in the comic indulge in this celebration by sarcastically pretending to be upset about the potential for pathogen extinction, while in reality being excited about the possibility. The title text mentions some of the species on the list, including polio and Guinea worm disease - diseases that have historically sickened and killed many people but are currently being eradicated due to worldwide efforts - the former, famously, through vaccination, and the latter through education and prevention techniques. As their eradication proceeds, they become more and more endangered of extinction, and thus earn their place on the list. The title also mentions a much less important pathogen, namely a certain strain of an enterovirus , also known as a stomach flu, which unlike polio and guinea worm is likely only to cause temporary discomfort, not death or long-term disability, in infected people. However, the strain in question infected every member of the lab maintaining the list, and as a result of their personal negative experience with it, and the spiteful feelings that resulted from that experience, the characters will celebrate its extinction as much as that of polio, and have accordingly added it to the list. Randall was most likely inspired by this article about different influenza strains. Influenza causes the yearly flu, which infects 5–15% of the global population annually and causes 3-5 million severe cases worldwide. The bitter irony here is that much recent scholarship has described links between parasite biodiversity and ecosystem-wide, indeed planet-wide, biodiversity . In a few cases, if preserving and expanding biodiversity are seen as good things, then preserving and expanding biodiversity of parasites is a good thing, the one not being possible without the other. Parasites and disease agents, arguably, are classes of predators, and their removal can help establish a superpredator, the actions of which can catastrophically drive down biodiversity. Humans, released from predation by a large percentage of formerly-effective microbial predators, through the introduction of penicillin and other antibiotics plus other elements of 'heroic medicine', sanitation, etc., have arguably become such a superpredator , and one that is mediating a loss of global biodiversity that may become the largest single species-extinction event in the history of planet Earth. There also seems to be some evidence that infections with influenza viruses increase the chance of a heart attack. For instance regular flu shots reduce the risk of heart attacks . Thus the fact that we are "heartbroken" when B/Yamagata goes extinct could be sarcastic since we might suffer less from broken hearts. [Ponytail stands facing Cueball and Megan in front of a poster board.] [Ponytail is pointing a stick to the board reading "Current List" with bullet points beneath.] [The first bullet reads Influenza B/Yamagata.] [Four further bullet points follow, which are left indistinct.] Ponytail: Influenza's genetic diversity has declined during the pandemic, and the B/Yamagata lineage is at risk of extinction. Ponytail: Which would be such a shame. Megan: Yeah, I'm sooooooo worried about it. Cueball: We'd be just heartbroken! [Caption below the panel]: When a pathogen that scientists really don't like is close to disappearing, it gets added to the sarcastic endangered species list.

Comet Visitor

Comet Visitor

https://www.xkcd.com/2524

https://www.explainxkcd.com/wiki/index.php/2524:_Comet_Visitor

[Megan sits at a desk in front of a computer, looking to the left off-panel and pointing at the screen] Megan: Have you seen this big comet, C/2014 UN271? Megan: It'll pass near Saturn's orbit in 10 years. [In a frameless panel, Cueball stands behind Megan, who is now looking at the computer and typing] Cueball: Wow, look at the orbital period. Megan: Yeah, it hasn't been to this part of the solar system since humans evolved. Megan: At least. [Cueball starts running off-panel, holding his finger in the air. Megan looks towards him with both arms resting on the back of her chair] Cueball: Well, we definitely need to tidy up. I'll start on the Pacific Garbage Patch, you tackle orbital debris. Megan: What about the moon footprints? Cueball: Sweep them up. Collect the Mars rovers, too! Cueball: We can put them back once it's gone.

Comet C/2014 UN 271 is a large comet that was discovered in 2014 almost as far from the Sun as the orbit of Neptune, and it will reach its closest approach in 2031, near Saturn's orbit. It's an Oort Cloud comet, with a period of more than 4 million years. Since modern humans ( homo sapiens ) evolved about 300,000 years ago (although tool-making ancestors were around about 2.5 million years ago), the last time it was among the planets was indeed long before humans evolved. When a long-period comet comes into the inner Solar System, it's often figuratively called a "visit". But Megan and Cueball treat this more literally (or perhaps more sarcastically). Just as one usually neatens up their home when they're expecting guests, to make a good impression, they realize they need to clean up the Earth and its vicinity in preparation for this "visitor". Cueball starts handing out assignments -- he'll clean up the Pacific Garbage Patch , and suggests that Megan take care of all the debris in orbit . Cueball and Megan also make notes to sweep up the lunar footprints that NASA astronauts left on the Moon during the Apollo missions and put away the Mars rovers . It's also common for people expecting visitors to put various objects out of view with the intention of returning them to their normal place after the visit, usually because the objects are considered unsightly that under normal circumstances is outweighed by the convenience of being out in the open. However, since the comet will not come anywhere close to Earth and Mars, all this hardly seems necessary; it would be like cleaning up your home because the President or some other dignitary will be visiting your town. In addition, while a dignitary would theoretically be able to see one's house, although comets have tails , they do not have eyes, [ citation needed ] so they would not be able to perceive any difference between Earth before and after tidying up (even if the nucleus had an eye, it would not be able to see because it is in a coma ). Furthermore, sweeping footprints in the Moon, that Cueball sees as a way of tidying up, would be seen as destroying an invaluable archaeological sites by NASA and other people . Alternatively, Megan and Cueball aren't "cleaning up" for a visitor as one might do if the visitor was a friend of theirs. They're hiding themselves and contraband as one might do if they were worried the police were visiting. Or more likely in this context that it could be an alien visit, and they would like to make it difficult to spot the human civilization from space. In that case they might need to shut down all light in every big city on Earth as well. The title text debunks the claim that the Great Wall of China is the only human-made structure visible from outer space ; in fact the Great Wall cannot easily be distinguished from space (as it is very long but not wide), but some other human constructions such as the Pyramids can (and cities are easily visible at night because they emit light). [Megan sits at a desk in front of a computer, looking to the left off-panel and pointing at the screen] Megan: Have you seen this big comet, C/2014 UN271? Megan: It'll pass near Saturn's orbit in 10 years. [In a frameless panel, Cueball stands behind Megan, who is now looking at the computer and typing] Cueball: Wow, look at the orbital period. Megan: Yeah, it hasn't been to this part of the solar system since humans evolved. Megan: At least. [Cueball starts running off-panel, holding his finger in the air. Megan looks towards him with both arms resting on the back of her chair] Cueball: Well, we definitely need to tidy up. I'll start on the Pacific Garbage Patch, you tackle orbital debris. Megan: What about the moon footprints? Cueball: Sweep them up. Collect the Mars rovers, too! Cueball: We can put them back once it's gone.

Air Travel Packing List

Air Travel Packing List

https://www.xkcd.com/2525

https://www.explainxkcd.com/wiki/index.php/2525:_Air_Travel_Packing_List

[A lists of 20 items is given in two columns with 10 items in each. Each item is preceded by a checkbox. Most items only take up one line, but in the left column two items take up two and in the right one item take up three, so they take up the same space. Above is a large heading, with an explanation beneath it.] Air Travel Packing List If you haven't flown in a while, you might not remember what you need to bring. Use this handy checklist to pack! [Left column:] ☐ Seat cushion ☐ Parachute ☐ Wing glue ☐ Air horn ☐ Sextant ☐ Nose plugs and goggles for pressure ☐ Airplane shoes ☐ Navigation crystal ☐ Spare batteries in case the plane runs out ☐ Birdseed [Right column:] ☐ Homing beacon ☐ Meteorite antidote ☐ USB wing connector ☐ Emergency siren ☐ Spare flaps ☐ Mouthpiece (Pandemic restriction; airlines still provide the trumpet) ☐ Luggage ballast ☐ Flag (International flights) ☐ Decoy tickets ☐ Keys to the plane

This comic is another in a series of comics related to the COVID-19 pandemic . The comic is about a proposed air-travel packing list, and the humor stems from the fact that many people have not been flying during the pandemic, and thus they might have forgotten what to pack. So Randall is so kind as to provide a packing list with 20 items. However, apart from the first item, the rest is not something you would or even should normally bring on an airplane. Many of the items are already found on passenger airplanes, some items would seem like they could be useful on a plane, while others could actually be useful in case of a plane crash (but only if you survive), while many others would be counter-productive to safe air travel, even in the event of a crash. Below in the table is a quick summary of each item. The title text references the idea that there is a trumpet for each passenger provided by the airline, which is item number 16 on the list. This items also states that you, because of the COVID-19 pandemic, should remember to bring your own mouthpiece for the trumpet as a safety measure. The trumpet idea is then combined with the common debate regarding reclining your seat in airplanes. About half of the people think that reclining is rude as it takes up the space of the person behind you. The other half think that seats recline for a reason and the person in a seat has the rights to the space behind them. See for instance this video about such a debate. Reclining a seat has resulted in actual physical fights on board airplanes. Here it seems that Randall sides with the anti-recliners, although maybe only in the context of the comic, because he states that reclining would prevent him from playing his trumpet, as the seat hits the bell of the trumpet. The person in front could certainly argue that playing the trumpet behind them would be very annoying, to which Randall could reply that because the trumpet is provided by the airline, he has the right to play it. This would add a new layer to the debate. This could also be Randall's way of arguing against the right to recline a seat, just because it is possible. [A lists of 20 items is given in two columns with 10 items in each. Each item is preceded by a checkbox. Most items only take up one line, but in the left column two items take up two and in the right one item take up three, so they take up the same space. Above is a large heading, with an explanation beneath it.] Air Travel Packing List If you haven't flown in a while, you might not remember what you need to bring. Use this handy checklist to pack! [Left column:] ☐ Seat cushion ☐ Parachute ☐ Wing glue ☐ Air horn ☐ Sextant ☐ Nose plugs and goggles for pressure ☐ Airplane shoes ☐ Navigation crystal ☐ Spare batteries in case the plane runs out ☐ Birdseed [Right column:] ☐ Homing beacon ☐ Meteorite antidote ☐ USB wing connector ☐ Emergency siren ☐ Spare flaps ☐ Mouthpiece (Pandemic restriction; airlines still provide the trumpet) ☐ Luggage ballast ☐ Flag (International flights) ☐ Decoy tickets ☐ Keys to the plane

TSP vs TBSP

TSP vs TBSP

https://www.xkcd.com/2526

https://www.explainxkcd.com/wiki/index.php/2526:_TSP_vs_TBSP

Cooking tips: tsp vs tbsp [left column:] Tsp Teraspoon 1,000,000,000,000 (10 12 ) spoons [right column:] Tbsp Binary tsp 1,099,511,627,776 (1024 4 ) spoons

This is another one of Randall's Tips , this time a Cooking Tip. This comic plays a joke on the common liquid measurements of teaspoons (tsp) and tablespoons (tbsp), which are commonly confused. In the US, a teaspoon is defined as 4.9 ml (0.18 imp fl oz; 0.17 US fl oz) while a tablespoon is defined as 14.8 ml (0.50 US fl oz; 3 tsp). It also plays a joke on metric prefixes (based on powers of 10) versus binary prefixes (based on powers of 2), which are also a common source of confusion (see also 394: Kilobyte ). In the International System of Units (SI), T (for tera- ) signifies a multiplier of 10 12 (that is, 1 000 000 000 000), while Ti ( tebi- , for terabinary ), and not Tb, is an ISO standard binary prefix meaning 2 40 (that is, 1024 4 = 1 099 511 627 776). If "spoon" is understood as US teaspoon, then one teraspoon will be 4 928 922 cubic meters (1.302 billion US gallons or 3996 acre-feet) and a binary teraspoon will be 5 419 407 cubic meters (1.432 B gal or 4394 acre-ft). If the US tablespoon is taken as base unit, a teraspoon will be 14 786 765 cubic meters and a binary teraspoon 16 258 220 cubic meters – roughly equivalent to six thousand Olympic-size swimming pools or slightly more than six times the volume of the Pyramid of Giza. All these units have fairly limited uses in cooking. [ citation needed ] The title text is a play on a lyric from the Alanis Morissette song " Ironic ": "It's like ten thousand spoons when all you need is a knife." Randall changes the line to "teraspoon" and "kilonife". The "kilonife" comes from knife being interpreted as "nife" with a k prefix – k being the SI symbol for kilo- –, in a similar vein as taking tsp for "teraspoon". "Nife" is a geophysical name for Earth's core, thought to be composed of nickel and iron, and hence the word comes from the chemical symbols Ni (nickel) and Fe (iron). Cooking tips: tsp vs tbsp [left column:] Tsp Teraspoon 1,000,000,000,000 (10 12 ) spoons [right column:] Tbsp Binary tsp 1,099,511,627,776 (1024 4 ) spoons

New Nobel Prizes

New Nobel Prizes

https://www.xkcd.com/2527

https://www.explainxkcd.com/wiki/index.php/2527:_New_Nobel_Prizes

[Megan stands at a podium on a stage, facing right. Behind her is a screen showing eight Nobel Prizes. Ponytail is approaching the front of the stage while waving.] Megan: And all eight Nobel Prizes for the Discovery of New Nobel Prizes have been awarded to... Megan: *sigh* Megan: ...Doctor Adams, again , for the discovery of two new Prizes. Dr. Adams: Thank you, thank you! [Caption below frame:] We don't know how she started this and now we can't figure out how to stop her.

The Nobel Prize is a set of prizes awarded in memory of Alfred Nobel to, "those who, during the preceding year, have conferred the greatest benefit to humankind." In this comic a Nobel prize is being awarded for the discovery of two new Nobel prizes. This parallels Nobel Prizes awarded for the discovery of new elements . However, unlike elements, Nobel Prizes cannot be discovered. [ citation needed ] The comic suggests that the doctor, presumably a social psychologist and the world's top expert on Impostor Syndrome , being awarded the prize came up with the idea of "discovering" Nobel Prizes, and no one can figure out how to stop awarding them to her. In reality, the categories were established by Alfred Nobel's will for contributions or discoveries in the fields of Physics, Chemistry, Physiology or Medicine, Literature, and Peace. In 1968, Sweden's central bank funded an award for economics in honor of its 300th anniversary that is also colloquially called the Nobel Prize in Economics . While there is currently a petition to add a Nobel prize for contributions to environmental conservation, it would presumably also need external funding, although the decision process is unclear. The title text is a play on the Nobel Prize in Physiology or Medicine , insinuating that the Nobel Assembly (the group in charge of awarding Nobel Prizes) has become so desperate to stop Doctor Adams that they have decided to award a Nobel Prize to anyone who can make her stop 'discovering' new prizes. The joke also plays on the name of the said prize, because as of the writing of this comic the Nobel Prize in Physiology or Medicine is the only Nobel Prize with two subjects (i.e. with "or" in the title). This may also be a jab by Randall at the fields of Physiology and Medicine, as poking fun at other disciplines is a recurring theme on xkcd. [ citation needed ] This comic was published on the Monday the week following the announcements of the 2021 Nobel Prize recipients. [Megan stands at a podium on a stage, facing right. Behind her is a screen showing eight Nobel Prizes. Ponytail is approaching the front of the stage while waving.] Megan: And all eight Nobel Prizes for the Discovery of New Nobel Prizes have been awarded to... Megan: *sigh* Megan: ...Doctor Adams, again , for the discovery of two new Prizes. Dr. Adams: Thank you, thank you! [Caption below frame:] We don't know how she started this and now we can't figure out how to stop her.

Flag Map Sabotage

Flag Map Sabotage

https://www.xkcd.com/2528

https://www.explainxkcd.com/wiki/index.php/2528:_Flag_Map_Sabotage

[A flag displays a white country-shaped area surrounded by a red field. Inside the shape sits a map legend.] [Label of map legend] Map Legend [Bright blue rectangle] Disputed territory [Green rectangle] Newly independent [Blue rectangle] Demilitarized zone [Yellow rectangle] Tornado warning [Dark blue rectangle] Held by rebel forces [Red rectangle] Greater Delaware [Black rectangle] Unexplored [Caption below panel] Our new country's flag sabotages those maps where geographic areas are colored in with flag patterns.

The comic refers to a type of map that colors countries using the national flag designs; see here for such a map of Europe. Randall proposes a new flag specifically designed to troll such maps. Most obviously, the flag includes a legend with multiple common flag colors to indicate random regional attributes. Hence, the mere act of placing this flag on a map would cause people to misinterpret this legend as applying to the entire map, giving wildly false information about regions of other countries. This trick is reminiscent of 327: Exploits of a Mom , with Mrs. Robert's son Robert'); DROP TABLE Students;-- . In addition to the legend, the flag consists of two red fields, one of which has an irregular-shaped border, the other of which is a straight line. The irregular shape is similar to a geographical border based on natural features (such as rivers and coastlines), while borders not based on such features tend to be straight lines. Red is the most common color on national flags, so if any bordering country had red on their flag, it would risk bordering these red fields, confusing where the border lay (as well as designating the entire red region as "greater Delaware"). If this flag is intended for the USA (although the text mentions "our new country"), the red regions would be continuous with the red strips on both sides of Canada's flag and the red field on the right of Mexico's flag, disguising the border still further. The title text refers to the flag of Belgium, which consists of three vertical stripes in the order (left to right) black, yellow, and red. The western part of Belgium would, according to the legend, be unexplored, while the eastern part would be Greater Delaware. The middle would therefore be a tornado zone separating the unexplored area from Greater Delaware. Depending on how the flags are aligned it might be possible to explore from the south, where the blue-white-red stripes of the French flag contain another piece of Greater Delaware that may be conveniently located to help said exploration. Exploring from the Netherlands (red, white, and blue horizontal stripes) is not viable as rebel forces are positioned between Greater Delaware and the unexplored region. This is not the first time Randall has made a flag for a new country! See 1815: Flag [A flag displays a white country-shaped area surrounded by a red field. Inside the shape sits a map legend.] [Label of map legend] Map Legend [Bright blue rectangle] Disputed territory [Green rectangle] Newly independent [Blue rectangle] Demilitarized zone [Yellow rectangle] Tornado warning [Dark blue rectangle] Held by rebel forces [Red rectangle] Greater Delaware [Black rectangle] Unexplored [Caption below panel] Our new country's flag sabotages those maps where geographic areas are colored in with flag patterns.

Unsolved Math Problems

Unsolved Math Problems

https://www.xkcd.com/2529

https://www.explainxkcd.com/wiki/index.php/2529:_Unsolved_Math_Problems

The Three Types Of Unsolved Math Problem [First box:] Weirdly Abstract [Ponytail stands in front of an equation.] Is the Euler Field Manifold Hypergroup Isomorphic to a Gödel-Klein Meta-Algebreic ε<0 Quasimonoid Conjection under Sondheim Calculus? Or is the question ill-formed? ⬙ℝ̇ℤ/Eℵ₅ [The Z is raised and underneath it is a double-ended arrow bent at a right angle. One points toward the R the other toward the Z. The ₅ is double-struck (𝟝) like the R and Z.] Second: Weirdly Concrete [Cueball stands in front of a grid with 6 columns and 7 rows] If I walk randomly on a grid, never visiting any square twice, placing a marble every N steps, on average how many marbles will be in the longest line after N*K steps? Somehow the answer is important in like three unrelated fields. [The path starts in the 3rd row and 3rd column, a small circle indicates the start. It takes the path: North, East, North, East (a black dot representing the 1st marble is placed here, so N=4), South, East, South, South (2nd marble), West, South, West, North (3rd marble), West, South, South, South (4th Marble), West, North, West, West (this goes offgrid to the West. There is no visible line or marble outside the grid). The 1st, 3rd, and 4th marbles are colinear and there is a dotted line connecting them. The line's slope is 3.] Third: Cursed [A Megan with unkempt hair stands next to a curve] What in God's name is going on with this curve? Is it even math? [The curve starts at the bottom of the screen, rises straight upward, begins to wobble left and right a little. It lists to the left and the left-right motion increases, then decreases. It begins a large counter-clockwise arc, spiraling inwards twice, then ends]

Math has many problems that remain "unsolved." This is not simply a matter of finding the correct numbers on both sides of an equal sign, but usually require proving or finding a counterexample to some conjecture, or explaining some property of some mathematical object. Sometimes this might involve extending an existing proof to a wider range of numbers like reals, complex numbers, or matrices. A concrete problem is one that is very obviously connected to a real world process, while an abstract problem is one which seems unconnected to actual problems. In modern math, many problems tend to be very abstract, requiring complicated notation to adequately state the problem in the first place, like many of the millennium problems . On the other hand, many unsolved problems are very concrete; for example, there are very many problems related to packing objects into spaces that are very difficult to solve although quite easy to state, such as the Collatz conjecture . Finally, Randall describes a third category of "cursed problems," that have strange, seemingly random behavior, such as the behavior of turbulence or the distribution of prime numbers. In the first panel, Ponytail describes a weird abstract problem. Her description seems to be a meaningless jumble of terms that are either mathematical or just sound mathematical. And the mathematical terms are from disparate branches of mathematics: group theory, topology, and calculus. Finally she asks whether the problem statement is ill-formed; considering that it's mostly gibberish, this may be true. Many real unsolved math problems appear similarly abstract. One example is the Hodge conjecture , a Millennium Prize problem. It states "Let X be a non-singular complex projective manifold. Then every Hodge class on X is a linear combination with rational coefficients of the cohomology classes of complex subvarieties of X." These words may appear nonsensical to a layperson. And even to an expert, the question is `abstract'. (Given a specific manifold, even an abelian fourfold, how on earth do you determine if a given 2,2 class is a cycle?) In the second panel, Cueball describes a concrete random walk problem, and then mentions that this somehow has applications in three unrelated fields. This is actually not uncommon. The Wikipedia article says that "random walks have applications to engineering and many scientific fields including ecology, psychology, computer science, physics, chemistry, biology, economics, and sociology. Walking randomly on a grid never visiting any square twice is known as a self-avoiding walk ." This panel may have been inspired by some of the tricky unsolved problems about self-avoiding walks. Many of these problems have to do with rigorously proving properties of random walks that have been guessed by physics intuition, so these problems are connected to physics. The part about the maximum number of points in a line is reminiscent of problems in combinatorial geometry, which often involve counting points lying on different lines. Python code simulating this situation can be found here: [1] . C++ code simulating this situation can be found here: [2] . In the final panel, Megan is looking at a strange curve that seems to have no consistent pattern. At the bottom it's mostly straight, with a few little wobbles. In the middle it looks like a wild, high-frequency wave that suddenly bursts and then dies down. And the top is a spiral that looks like a question mark or a Western-style Crosier . She wonders if this could even be mathematical. On one hand, considering the weird shapes that come from plotting some mathematical processes (e.g. the Mandelbrot set ), it could well be. For example the unsolved Riemann hypothesis , another Millennium Prize problem, concerns the properties of a weird and at-first-glance random curve . In number theory, the term "cursed curve" has been used to describe the "split Cartan" modular curve of level 13, which resisted attempts for many years to compute its set of rational points . On the other hand, the question if could even be mathematical suggests that this may indeed not be a mathematical symbol. The curve looks like the unalome symbol, which is a Buddhist symbol which represents the path taken in life, or the journey to enlightenment. It could be argued that this indeed represents an unsolved problem, although not a mathematical one - which might then be part of the humoristic meaning. In the title text, the curve in the final panel is further explained based on the consensus of supposedly a group who has studied it and the procedure that generates it, commenting that "it's just like that" as their conclusion, which is really not an explanation at all. The Three Types Of Unsolved Math Problem [First box:] Weirdly Abstract [Ponytail stands in front of an equation.] Is the Euler Field Manifold Hypergroup Isomorphic to a Gödel-Klein Meta-Algebreic ε<0 Quasimonoid Conjection under Sondheim Calculus? Or is the question ill-formed? ⬙ℝ̇ℤ/Eℵ₅ [The Z is raised and underneath it is a double-ended arrow bent at a right angle. One points toward the R the other toward the Z. The ₅ is double-struck (𝟝) like the R and Z.] Second: Weirdly Concrete [Cueball stands in front of a grid with 6 columns and 7 rows] If I walk randomly on a grid, never visiting any square twice, placing a marble every N steps, on average how many marbles will be in the longest line after N*K steps? Somehow the answer is important in like three unrelated fields. [The path starts in the 3rd row and 3rd column, a small circle indicates the start. It takes the path: North, East, North, East (a black dot representing the 1st marble is placed here, so N=4), South, East, South, South (2nd marble), West, South, West, North (3rd marble), West, South, South, South (4th Marble), West, North, West, West (this goes offgrid to the West. There is no visible line or marble outside the grid). The 1st, 3rd, and 4th marbles are colinear and there is a dotted line connecting them. The line's slope is 3.] Third: Cursed [A Megan with unkempt hair stands next to a curve] What in God's name is going on with this curve? Is it even math? [The curve starts at the bottom of the screen, rises straight upward, begins to wobble left and right a little. It lists to the left and the left-right motion increases, then decreases. It begins a large counter-clockwise arc, spiraling inwards twice, then ends]

Clinical Trials

Clinical Trials

https://www.xkcd.com/2530

https://www.explainxkcd.com/wiki/index.php/2530:_Clinical_Trials

1. Come up with new idea 2. Convince people it's good [Scrawled in red as an afterthought, an arrow inserting it between item 2 and the original item 3] 3. Check whether it works 3. [Now scribbled over and amended to "4."] New idea is adopted [Caption below the panel] The invention of clinical trials

The comic begins with a simple process for adopting a new idea just by convincing people that it is a good idea. The joke is that this skips the important step of checking whether it actually is a good idea. That correction presumably comes about after ideas are adopted which sounded good but turn out to be harmful. The comic captions the addition of this checking step as "the invention of clinical trials". The purpose of clinical trials in medicine is to make sure that a new medicine works and doesn't have serious side-effects. One example of the dangers of failing to make sure that it doesn't have serious side effects is thalidomide , which caused a lot of birth defects. In a clinical trial, the effect of a treatment is compared to the effect of a placebo, or an existing treatment, to make sure it actually has a beneficial effect. (Earlier trials establish that it is even a viable candidate for testing and establishing possible dosages/regimens that can then be carried forward to a treatment (Phase III) trial.) Before the invention of clinical trials, people generally didn't know, or at least had no way of confirming, whether medicines actually worked. Although many herbs and medicines were effective, others were no better than a placebo, and some medical treatments such as trepanation and bloodletting not only had no benefit (except for a very few rare conditions) but were very likely to be harmful. Those treatments that did work at all were mostly those that had been tried (for whatever reason ) and just happened to be useful, but others had neutral or even adverse effects, but still managed to not be so dangerous that subsequent recoveries from the original ailment—regardless of (or despite!) dangers inherent in such treatments—were taken as proof of their efficacy. Similar to more recent examples, some earlier treatments may have been gradually discovered to help a particular condition only by noticing beneficial side-effects when consumed for sustenance or for unrelated medical 'guesses'. However, they also remained without the full scientific rigour so long as it remained a 'traditional remedy' with at best an oral tradition across many disparate practitioners, and no consistent effort to formalise or test the falsifiability of any findings. At the time that this comic was published, the world was in the middle of the COVID-19 pandemic , which made the existence of clinical trials more relevant to the public, who waited eagerly for what sounded like good ideas to get through clinical trials and available to the general public… or fail clinical trials and not do that. During this frustrating wait, many unscientific claims have been made that various drugs or non-drug treatments are cures for COVID-19, making it difficult to convince believers to get real treatments. On the other hand, many people were skeptical about COVID-19 vaccines which were made available to the public for emergency use before the clinical trials were finished, or had concerns about whether the clinical trials were rushed or otherwise flawed due how quickly they were conducted compared to the traditional speed for vaccine development and approval. In the title text, "Standard of care" refers to the previously accepted practice which a new medicine needs to be compared against. Because the original 3-step "standard of care" in this comic didn't include clinical trials before their adoption, we didn't need to do any testing in order to decide to start using them. If we had had them as the standard of care, then we would have had to perform tests before we added a step and it would have taken longer. This assumes that the process itself is subject to the same scientific rigor as medical treatment; in practice that would be more of a political change that is still not tested. This comic can be viewed to criticize several extreme political proposals that are obviously bad ideas to most people, such as abolishing the nuclear family, making gay marriage illegal, blocking the development of renewable energy sources and defunding the police. People tested the latter in Seattle, and the test didn't go well . 1. Come up with new idea 2. Convince people it's good [Scrawled in red as an afterthought, an arrow inserting it between item 2 and the original item 3] 3. Check whether it works 3. [Now scribbled over and amended to "4."] New idea is adopted [Caption below the panel] The invention of clinical trials

Dark Arts

Dark Arts

https://www.xkcd.com/2531

https://www.explainxkcd.com/wiki/index.php/2531:_Dark_Arts

[Cueball and White Hat stand in a slightly darkened room, with a jagged circle of light centered on Cueball and light-reflecting onto White Hat's face. Cueball holds his arm out with his palm facing towards White Hat.] Cueball: Long ago, in another age, I mastered these dark arts. Cueball: But I now endeavor to live my life such that I never need them. Cueball: Their power leads only to ruin. [Caption below panel] My response whenever anyone asks me to mess around with filesystems

White Hat has presumably just asked Cueball to perform some task involving filesystems . Cueball responds with an exceptionally melodramatic monologue, referring to the subject as "dark arts" and stating he'd rather not have anything to do with them. This is reminiscent of a fairly typical scene in fantasy novels, superhero movies, etc: a person with supernatural powers explains they prefer not to use them, as their use is likely to have negative effects that outweigh the positive ones. Often this is tied to a tragic backstory of the character, where the use of their powers previously caused them or someone close to them much suffering. The humor of the comic comes from the parallel drawn; it seems unlikely that knowledge of filesystems could have negative consequences on the scale of, say, leveling a city, so the comparison is hyperbolic. However, much of today's infrastructure does depend on legacy systems that can be very overly complex to work with, having weathered aggressive political conflicts and short corporate deadlines for decades now. An example is the recent shutdown of the pgp keyserver network, or how the developer of the fastest linux filesystem built (reiserfs) was imprisoned for murdering his wife right before it could be merged into linux. Still, this joke is in a similar vein to comics like 349: Success , in which Cueball's relationship with technology is shown to have a potential for disaster far exceeding that of a normal person's. A filesystem is the part of a computer's operating system that handles the organization of data in persistent storage, usually splitting it into files and directories. It can be a very complicated piece of software. Because of this, it is easy to make mistakes in advanced usage, and because it controls practically all data on a given machine, mistakes made can have serious consequences (e.g., loss of data). These properties of filesystems are likely why Cueball is reluctant to mess with them. ext4 is a popular filesystem used with the Linux operating system kernel. Hardlinks allow two filenames to refer to the same underlying file or directory. These can be particularly tricky to use, as in nearly all respects they look like regular files, but modifying them can have effects that are not immediately obvious (e.g., changing what one filename refers to, the other will not remain consistent). Hardlinks and their misuse have been referenced in xkcd before, as in 981: Porn Folder . The title text hints at an experience Cueball or Randall had (his own "tragic backstory", if you will), involving hardlinks on ext4. He thought he had found an ideal use case for them, one which presumably avoided most of their pitfalls, but still, six months later, ended up having to troubleshoot some inscrutable bug arising from his decision. Javascript is a programming language most often associated with web pages. As such it is not usually interacting directly with a computer's filesystem, since allowing arbitrary websites to access the filesystem is widely considered an extremely bad idea [ citation needed ] . It is possible to run Javascript directly outside of a browser – in which case it does have access to common filesystem operations, and even theoretically to the internals of the filesystem – but since it is a high-level language with poor support for working with the data structures a filesystem uses, this would be a painful, "cursed" way to go about things. A senior IT professional (nowadays fewer people need to know about such features) will be reminded of their own experiences and mishaps with non-trivial file system configurations. Beyond hardlinks, filesystems may have a number of features a normal user or even an admin are not aware of. Such features are prone to bugs, poor documentation, or poor integration with other system tools. For example: "In another age" might refer to the fact that detailed file system manipulations were common in the days when developers were installing, configuring and managing operating systems and software on physical servers. When disk space was limited and network speeds were low, such manipulations saved space and time. Virtualization, containerization and deployment frameworks isolate developers and administrators from such low level details. [Cueball and White Hat stand in a slightly darkened room, with a jagged circle of light centered on Cueball and light-reflecting onto White Hat's face. Cueball holds his arm out with his palm facing towards White Hat.] Cueball: Long ago, in another age, I mastered these dark arts. Cueball: But I now endeavor to live my life such that I never need them. Cueball: Their power leads only to ruin. [Caption below panel] My response whenever anyone asks me to mess around with filesystems

Censored Vaccine Card

Censored Vaccine Card

https://www.xkcd.com/2532

https://www.explainxkcd.com/wiki/index.php/2532:_Censored_Vaccine_Card

[Profile picture of a Cueball's head and shoulders, with unreadable lines of text to the right.] Check it out, I just got my booster! [Picture of the U.S. COVID-19 Vaccination Record Card attached on a media post. The card includes pre-printed information in black and handwritten information in blue, the latter indicated here by bold text. Some of the text has been blacked out, indicated here by "[censored]".] COVID-[censored] Vaccination record card [At the upper right of the card appears the logo of the U.S. Department of Health and Human Services, a stylized eagle surrounded by the words "Department of Health & Human Services USA", although those words are not legible in this drawing. Next to that appears the logo of the Centers for Disease Control and Prevention, a shaded box with the letters "CDC" and the words "Centers for Disease Control and [censored]" below it.] Please keep this record card, which includes [censored] about [censored]. Por favor, guarde esta tarjeta de registro, que incluye [censored] [censored] sobre [censored]. Munroe Randall Last Name First Name 10-17-[censored]84 41592653 Date of birth Patient number [A table fills the remainder of the card. It has four columns and five rows. The first row gives the column names:] Vaccine. Manufacturer lot number. Date. Provider or clinic site. [The rest of the rows have been filled out. Each "date" cell also includes pre-printed "MM DD YY" below the line where the date is written.] 1st dose COVID-[censored]. Pfizer ER1138 . 04 / 01 / 21 . CVS Pharmacy Clinician #5309 . 2nd dose COVID-[censored]. Pfizer ES2187 . 04 / 22 / 21 . CVS [censored] [censored]. Other. 3rd dose [censored] FH1729 . 10 / 21 / 21 . [censored] [censored] [censored] CIA [censored]. Other. [censored]. [censored]/[censored]/[censored]. [censored]. [Caption below panel:] Security tip: To seem more mysterious, try censoring only non -identifying information.

This comic is another entry in a series of comics related to the COVID-19 pandemic , specifically regarding the COVID-19 vaccine . The comic hinges on the sharing of vaccination card photos on social media as proof that the user has been vaccinated against COVID-19 (in this case, gotten a booster shot , a third dose of the vaccine). When people in the United States first started receiving their vaccine shots, a large number of them shared photos of the CDC vaccination proof cards that they received alongside the vaccines; it was enough of a trend that the FTC released an official statement warning vaccine recipients not to share photos , due to the cards containing personal identification that probably should not be made public. The irony here is that Randall has " censored " (redacted) some impersonal lines, such as the instructions that are identical on all vaccination cards, and many easy-to-guess lines, while not censoring any of said personal information. Considering the date of the 3rd dose (one day prior to the comic's uploading), it is likely that the blackouts in the last line are only covering whitespace. Another possible reference here is to the practice of filing for FOIA requests that has been getting more popular in recent years, with sites like muckrock.com developing to support it. These requests provide for citizens to view the contents of government files, but the files first go through a process of redaction via solid black rectangles. The information that is redacted can seem random, ridiculous, and frustrating, and be a source of legal action. The caption indicates that his intention is to "seem more mysterious". This is best exemplified by the blanking of most of the word "clinician" to leave the acronym " CIA ", referring to the US government agency known for its frequently "mysterious" (classified) activity, as well as its liberal use of redaction like that in the comic. The "19" in COVID-19 is systematically censored in the comic. This is humorous because currently COVID-19 is the only thing that could be meant by "COVID-[anything]", and so the redaction is pointless. This may also be intended, in the interest of mystery, to imply some future outbreak of a similar disease (given an identifier based on the year of its inception). The sentence at the top of the card, which appears once in English and once in Spanish, has equivalent portions redacted in both languages: This is the first comic including a sentence (or, given the censorship, at least a good portion of one) in Spanish. CVS Pharmacy is a pharmacy chain in the US which provides COVID-19 vaccinations. CVS #05309 is in Pineville, LA, while Randall lives in Massachusetts; it is not clear why he would have received his first vaccine dose in Louisiana. The title text comments on the "Provider or clinic site" of the second dose on the card. Where the word "pharmacy" appears in the previous row (and would be on a real card), it is censored in the comic. The most reasonable assumption is that the word is still "pharmacy" and that Randall has simply chosen to redact that instance for some reason, but the title text humorously implies that it was in fact some other CVS-related venture where he got his second dose, for instance a "CVS parking lot" or perhaps an anti-submarine warfare carrier . CVS's parent company, CVS Health , does have other enterprises with compatible names: CVS Caremark and CVS Specialty . However, neither of these provide COVID-19 vaccinations. Randall's patient number is the 2nd to 9th digits of the fractional part of the decimal expansion of pi inclusively: 41592653. The lot numbers of the first and second doses allude to two numbers that appear frequently in Star Wars and other works related to George Lucas: 1138 , and 2187 . The lot number of the third dose is the Ramanujan-Hardy number . The Clinician number for the first shot is the last 4 digits of the phone number for "Jenny" 867-5309 , which has been entered into communication technology by a massive number of people. Given the reasonable assumption [ citation needed ] that the partially censored year relates to the twentieth century, the date of birth on the card corresponds to that given in the acknowledged timeline for Randall. The censorship of that specific part of his date of birth might be related to the fact that the number "19" has been systematically redacted on the card. Another interpretation is that Randall is implying he is either over one hundred years old or a time traveler, although neither is likely to be true. [ citation needed ] [Profile picture of a Cueball's head and shoulders, with unreadable lines of text to the right.] Check it out, I just got my booster! [Picture of the U.S. COVID-19 Vaccination Record Card attached on a media post. The card includes pre-printed information in black and handwritten information in blue, the latter indicated here by bold text. Some of the text has been blacked out, indicated here by "[censored]".] COVID-[censored] Vaccination record card [At the upper right of the card appears the logo of the U.S. Department of Health and Human Services, a stylized eagle surrounded by the words "Department of Health & Human Services USA", although those words are not legible in this drawing. Next to that appears the logo of the Centers for Disease Control and Prevention, a shaded box with the letters "CDC" and the words "Centers for Disease Control and [censored]" below it.] Please keep this record card, which includes [censored] about [censored]. Por favor, guarde esta tarjeta de registro, que incluye [censored] [censored] sobre [censored]. Munroe Randall Last Name First Name 10-17-[censored]84 41592653 Date of birth Patient number [A table fills the remainder of the card. It has four columns and five rows. The first row gives the column names:] Vaccine. Manufacturer lot number. Date. Provider or clinic site. [The rest of the rows have been filled out. Each "date" cell also includes pre-printed "MM DD YY" below the line where the date is written.] 1st dose COVID-[censored]. Pfizer ER1138 . 04 / 01 / 21 . CVS Pharmacy Clinician #5309 . 2nd dose COVID-[censored]. Pfizer ES2187 . 04 / 22 / 21 . CVS [censored] [censored]. Other. 3rd dose [censored] FH1729 . 10 / 21 / 21 . [censored] [censored] [censored] CIA [censored]. Other. [censored]. [censored]/[censored]/[censored]. [censored]. [Caption below panel:] Security tip: To seem more mysterious, try censoring only non -identifying information.

Slope Hypothesis Testing

Slope Hypothesis Testing

https://www.xkcd.com/2533

https://www.explainxkcd.com/wiki/index.php/2533:_Slope_Hypothesis_Testing

[Three points are labeled "Student A", "Student B" and "Student C" from left to right in a scatter plot with axes labeled "Stats exam grade" (60-100) and "Scream loudness (decibels)" (86-94) with a trend line. Student B has the highest exam grade, followed by Student C and then Student A.] [A line goes from the trend line to a box containing the following:] β=1.94 p=0.586 [In a frameless panel, Megan reads a piece of paper while facing Cueball while three students look at them from the background.] Megan: Darn, not significant. Cueball: We need more data. Have them each try yelling into the mic a few more times. [The same scatter plot as in the first panel except with more points for each of the students with slightly different decibel values, and the text in the text box changed to:] β=1.94 p=0.037* *Significant! [Similar panel to the second one] Megan: Perfect! Cueball: Are you sure we're doing slope hypothesis testing right?

"Slope hypothesis testing" is a method of testing the significance of a hypothesis involving a scatter plot. In this comic, Cueball and Megan are performing a study comparing student exam grades to the volume of their screams. Student A has the worst grade and softest scream, but Student B has the best grades and Student C the loudest scream. A trendline has been plotted, indicating a positive correlation between grades and volume...but the p-value is extremely high, indicating little statistical significance to the trend. P-value is based on both how well the data fits the trendline and how many data points have been taken; the more data points and the better they fit, the lower the p-value and more significant the data. Megan complains about the insignificance of their results, so Cueball suggests having each student scream into the microphone a few more times. (The three students are still there as they can be seen behind them. The three students look like schoolkids; one of them is Science Girl .) Having the students scream again will not help though, because it only provides more data on the screaming without providing more data on its relation to exam scores, and is a joke around poor statistical calculations likely made in the field today. The p-value is incorrectly recalculated based on the increased number of measurements without accounting for the fact that observations are nested within students. Each student has exactly the same test scores (probably referencing the same datum as before) and have vocal volume ranges that don't drift far either (each seems to have a range of scream that is fairly consistent and far from overlapping). Megan is pleased by these results, but Cueball belatedly realizes this technique may not be scientifically valid. Cueball is correct (presuming that they are using simple linear regression). A more appropriate technique would account for the non-independence of the data (that multiple data points come from each person). Examples of such techniques are multilevel modeling and Huber-White robust standard errors. Measuring data multiple times can be a way to increase its accuracy, but does not increase the number of data points with regard to another metric, and the horizontally clustered points on the chart make this visually clear. A more effective and scientifically correct way of gathering data test would be to test other students and add their figures to the existing data, rather than repeatedly testing the same three students. Common statistical formulae assume the data points are statistically independent, that is, that the test score and volume measurement from one point don't reveal anything about those of the other points. By measuring each individual's scream multiple times, Cueball and Megan violate the independence assumption (a person's scream volume is unlikely to be independent from one scream to the next) and invalidate their significance calculation. This is an example of pseudoreplication. Furthermore, Megan and Cueball fail to obtain new test scores for each student, which would further limit their statistical options. Another strange aspect of their experiment is that the p-values obtained during a typical linear regression assume there is uncertainty in the y-values but the x-values are fully known, whereas in this experiment, they are reducing uncertainty in the x-values of their data, while doing nothing to improve knowledge of the y-values. Moreover, even if the new data were statistically independent, this still appears to be a classic example of "p-hacking", where new data is added until a statistically significant p-value is obtained. In current AI, there's a push toward "few-shot learning", where only a few data items are used to form conclusions, rather than the usual millions of them. This comic displays danger associated with using such approaches without understanding them in depth. Additionally, a common theme in some research is the discovery of correlations that do not survive independent reproduction. This is because randomness with too few samples produces apparent correlations, and Randall has repeatedly made comics about this hopeful error (see 111 , 925 and 882 among others). In the title text, Megan and Cueball are trying to yell over each other, asking each other to speak up so they can be heard, presumably because they are having trouble hearing from the yelling experiment. Or possibly they have trouble speaking audibly because they score poorly on statistics exams. [Three points are labeled "Student A", "Student B" and "Student C" from left to right in a scatter plot with axes labeled "Stats exam grade" (60-100) and "Scream loudness (decibels)" (86-94) with a trend line. Student B has the highest exam grade, followed by Student C and then Student A.] [A line goes from the trend line to a box containing the following:] β=1.94 p=0.586 [In a frameless panel, Megan reads a piece of paper while facing Cueball while three students look at them from the background.] Megan: Darn, not significant. Cueball: We need more data. Have them each try yelling into the mic a few more times. [The same scatter plot as in the first panel except with more points for each of the students with slightly different decibel values, and the text in the text box changed to:] β=1.94 p=0.037* *Significant! [Similar panel to the second one] Megan: Perfect! Cueball: Are you sure we're doing slope hypothesis testing right?

Retractable Rocket

Retractable Rocket

https://www.xkcd.com/2534

https://www.explainxkcd.com/wiki/index.php/2534:_Retractable_Rocket

[Beret Guy and Megan is talking. Behind them near the horizon is a tall rocket on a launchpad.] Beret Guy: We're testing our new retractable rocket. Megan: You mean reusable? Beret Guy: No. [A zoom in on the launchpad and rocket. It has the appearance of having a long first stage, a second stage with slightly wider fairing and an Apollo-style capsule with escape-tower atop it all. There is a directionless speech-bubble at the top depicting a count down voice.] Count down: Three...Two...One...Liftoff! [Same view as before, but while the base of the rocket-stack remains stationary, the first stage is apparently elongated, with a hint of a bend to the right, to raise the total height to which the upper-stage and capsule assembly reaches almost to the top of the panel.] [In a wider panel, with the base to the left, the first stage is now elongated far enough to disappear off the top of the center of the frame, thus clearly bending to the right. Two peoples voices are indicated as coming from the space capsule far above, as it reaches it destination.] Voice 1: Hi, welcome to the ISS! Voice 2: Hello! [The final panel shows the same view as in the third panel. The first stage is now retracting, and has similar length as in the third panel, but the capsule is no longer atop the 'second stage' fairing. Four movement lines above the top of the retracting rocket indicates that it is returning back to the original position.]

This comic documents another of Beret Guy 's absurdist ventures . He explains to Megan that "we" (possibly his company ) are testing their new "retractable" rocket. Reusable rockets are a growing industry, as they are more economically viable in the long run – though technically much more difficult to operate – than rocket boosters that are just discarded after use (which have been standard throughout the majority of space-faring history). Thus, Megan is understandably confused about Beret Guy's assertion that theirs is "retractable", asking if he misspoke. In typical fashion, he assures her that he did not misspeak, with a single "No" without further explanation. They proceed to watch the rocket "launch", proving that it is indeed retractable . In fact the rocket does not launch, but merely extends – apparently all the way to the International Space Station (ISS), a height of over 400 km (over 250 miles) – before retracting, as promised, to its original position. The top part, with the astronauts in it, has been left in space. Presumably, it is docked to the ISS, as the crew onboard the ISS say hello to them in panel 4. Of course, it would not be possible to extend anything this far. [ citation needed ] The top would need to be moving very fast compared to the bottom part, or it would bend westwards and break, and even with the strongest material a fully extended, very thin, presumably, hollow structure with a payload on top would buckle very soon after extension began. Also, the ISS moves at 27,600 km/h (17,100 mph) compared to the ground under it, making an orbit in about one and a half hours. So making the tip follow this long enough to dock would be even more impossible. Beret Guy's retractable rocket has more than a few similarities to a space elevator which has been discussed in real life. The chief difference is, a space elevator is only extended once (and most likely this would be down from space, not extended upwards), and never retracted unless it needs to be dismantled. Randall has referenced space elevators in 697: Tensile vs. Shear Strength . A more similar theoretical means to attain orbit is that of the space fountain . He has also examined the problems of a solid metal object extending through the atmosphere in a what-if . The current method of sending rockets into space requires huge amounts of fuel, and the more fuel you attempt to carry, the heavier the rocket, leading to more fuel being required, etc. ( Tsiolkovsky rocket equation ), which makes the current method inefficient. Alternate methods are being explored, such as using a slingshot ( SpinLaunch had a successful test flight of a smaller scale launcher just days before this comic was published, probably the influence for this comic), theoretical space elevators , or this comic's impossible retractable rocket idea, all of which would leave the majority of the "fuel" requirements on Earth or elsewhere rather than having to carry heavy fuel with the rocket. The only fuel carried might be minimal amounts for course adjustments once in space rather than large amounts used to get there. However, many of these methods are less flexible than rockets; the space elevator, for instance, operates on the basis of constant angular velocity relative to the Earth's axis of rotation, meaning that it cannot launch payloads directly into low-earth orbit, polar orbits, or many other orbits frequently used by satellites for their desirable characteristics, and satellites intended for these orbits might still need to carry considerable amounts of fuel, even if less than that required to launch directly from the ground. The title text parodies the 'old' single-use boosters. It appears that the predecessors to the 'retractable rockets' were capable of controlled extension only. Once they had lofted the payload to orbit, they were then allowed to fall over, destroying them in the process so they could not be used again just like booster rockets. However, if a 250 mile/400 km high construction just fell over, it would be much more difficult to avoid other damage, than to the rocket (booster), than for just a few small booster rockets falling out of the sky. [ citation needed ] This comic was released four days before (and possibly refers to) SpaceX's Crew-3 mission to send astronauts to ISS with a reusable rocket on 31 October 2021. [Beret Guy and Megan is talking. Behind them near the horizon is a tall rocket on a launchpad.] Beret Guy: We're testing our new retractable rocket. Megan: You mean reusable? Beret Guy: No. [A zoom in on the launchpad and rocket. It has the appearance of having a long first stage, a second stage with slightly wider fairing and an Apollo-style capsule with escape-tower atop it all. There is a directionless speech-bubble at the top depicting a count down voice.] Count down: Three...Two...One...Liftoff! [Same view as before, but while the base of the rocket-stack remains stationary, the first stage is apparently elongated, with a hint of a bend to the right, to raise the total height to which the upper-stage and capsule assembly reaches almost to the top of the panel.] [In a wider panel, with the base to the left, the first stage is now elongated far enough to disappear off the top of the center of the frame, thus clearly bending to the right. Two peoples voices are indicated as coming from the space capsule far above, as it reaches it destination.] Voice 1: Hi, welcome to the ISS! Voice 2: Hello! [The final panel shows the same view as in the third panel. The first stage is now retracting, and has similar length as in the third panel, but the capsule is no longer atop the 'second stage' fairing. Four movement lines above the top of the retracting rocket indicates that it is returning back to the original position.]

Common Cold Viruses

Common Cold Viruses

https://www.xkcd.com/2535

https://www.explainxkcd.com/wiki/index.php/2535:_Common_Cold_Viruses

[Megan, Cueball, and White Hat are standing in a group.] Cueball: COVID has made me so curious about colds. The next time I get one, I want to know which virus it is specifically. Cueball: A rhinovirus? RSV? Mild influenza? Or something weird like metapneumovirus? [They begin to talk together.] Megan: How distinct are they? Could you learn to tell them apart? Cueball: See, I wonder! White Hat: I could get a sequencer from work... [Caption above the panel:] Several years later... [In this panel, Cueball is sitting on the left, Megan is sitting on the right, and White Hat is standing at the far right. Megan is coughing, her hair frazzled. There is a tissue box in the middle, and discarded tissues lie on the ground.] Cueball: Ah yes, this one has the rich, full-bodied bouquet of RSV, but the heady congestion lends it a lingering rhinovirus nosefeel. Megan: *Cough* Megan: Quite right!

This comic is another entry in a series of comics related to the COVID-19 pandemic . In this strip, Megan and White Hat are listening to Cueball explain his newfound interest in the various different viruses that cause the common cold , which is an umbrella term used to describe the mild-to-moderate symptoms these viruses all cause. Megan expresses curiosity as well, and White Hat suggests he could get a DNA sequencer to help. By the third and final panel, several years have passed. All three characters appear to be ill, perhaps even as a result of now purposefully infecting themselves with chosen diseases. Whether deliberately or 'naturally', they do seem to have by now encountered a respiratory syncytial virus (RSV) and various types of rhinoviruses , and are now describing their experienced symptoms with terms similar to ones used in wine tasting (e.g. "bouquet" is a term used in wine tasting; "nosefeel" is a parody of the wine-tasting term "mouthfeel", etc.). This strip follows the theme of 915: Connoisseur , making fun of the fact that people can form strong opinions and preferences on pretty much anything if they spend enough time and attention on it. In this case, despite the fact that the symptoms of these viruses are almost universally considered to be unpleasant, the characters appear to have developed an appreciation for the subtle variations. A similar phenomenon is referenced in 1095: Crazy Straws . The idea of intentionally infecting a person with a disease is a trope in multiple Speculative Fiction stories. For instance, Iain M. Banks' Culture series , set in a world where all diseases are eradicated or treatable, includes story lines where persons deliberately infect themselves with viruses to experience the symptoms. The title text references the H1N1 swine flu virus, which was the disease at the heart of the 2009 swine flu pandemic . It also further expands on the wine tasting comparison – connoisseurs often consider the environmental conditions of the growing season the grapes came from as an important factor in the quality of a given wine, so certain years may be considered better than others. Since 2009, less severe forms of H1N1 influenza have become one of the standard variants in annual flu seasons and a perennial in the influenza vaccination mix. From the influenza strain's perspective, 2009 was the year of breakthrough success for H1N1. As access to community makerspaces, labs, and knowledge has spread, people have begun doing more things at home that were previously confined to industrial and academic research environments. This was stimulated further during the onset of the pandemic, when communities became focused on helping offset overtaxed national resources. [Megan, Cueball, and White Hat are standing in a group.] Cueball: COVID has made me so curious about colds. The next time I get one, I want to know which virus it is specifically. Cueball: A rhinovirus? RSV? Mild influenza? Or something weird like metapneumovirus? [They begin to talk together.] Megan: How distinct are they? Could you learn to tell them apart? Cueball: See, I wonder! White Hat: I could get a sequencer from work... [Caption above the panel:] Several years later... [In this panel, Cueball is sitting on the left, Megan is sitting on the right, and White Hat is standing at the far right. Megan is coughing, her hair frazzled. There is a tissue box in the middle, and discarded tissues lie on the ground.] Cueball: Ah yes, this one has the rich, full-bodied bouquet of RSV, but the heady congestion lends it a lingering rhinovirus nosefeel. Megan: *Cough* Megan: Quite right!

Wirecutter

Wirecutter

https://www.xkcd.com/2536

https://www.explainxkcd.com/wiki/index.php/2536:_Wirecutter

[A New York Times Wirecutter article. There is the NYT logo and Wirecutter logo in the top left. Also in the top of the page is a search bar, a user account icon, and 7 "header" level hyperlinks with illegible text. The article title is as follows:] The Best Religion By Wirecutter Staff [The words "Wirecutter Staff" are followed by illegible text presumably representing the date of the article. Below are icons for Twitter, Facebook, e-mail, and save.] [The article's image depicts Cueball shrugging in the center of the picture with many question marks floating above him. The content of the article is as follows:] What does it all mean? Our reviewers tried out over 70 of the most popular belief systems. Here's what they found…

Wirecutter is a product review website owned by The New York Times . Randall is parodying the website by having them "review" the 70 most popular religions . Product review websites typically make posts with the "best" X, e.g. "Best smartphones," or "Best laptops." These reviews are useful for consumers trying to choose among the wide variety of products available. There are a wide variety of religions . However, unlike electronic devices, a person does not usually choose their religion; they are taught one during childhood and most remain in that religion their entire life. Changing religions is ( usually ) a significant life event. [ citation needed ] Many religions, including many variants of the three major Abrahamic religions promote exclusivity , and do not recognize other religions as valid. They emphasize the importance of specific practices or belief in specific creeds. Members of those religions might not recognize a reviewer as having truly "tried" their religion if their intent was always to move on to another. A post "reviewing" religions is sure to stir up controversy, as many religious followers are passionate about their religious beliefs and believe their religion is best. Literal wars have been fought over the idea one religion could be superior to another, and it is not a wound most practitioners are willing to reopen any time soon. Moreover, religions are typically chosen for more fundamental reasons -- such as by comparing the likelihood that each religion makes accurate claims, or the efficacy of each religion in promoting an ethical life, or the connection a practitioner feels to the religion's rituals, metaphors, and images, or by privileging a preexisting cultural or family connection to a particular tradition -- not by comparing gimmicky features or price. The title text mentions "budget" and "upgrade" picks, which are subcategories for reviewers - cheaper options and options that are good for upgrading your current product. Neither of these categories are typical categories for religions [ citation needed ] and could further anger their adherents. The association of religion and money could allude to various controversial topics such as tithing , indulgences , televangelism , or Prosperity theology . Budget need not be just about money, it could also refer to the amount of time or effort involved. (e.g., how much time is spent in religious activities, needing to learn a new language, etc.) Some religious followers might be offended [ citation needed ] if their religion was picked in a "budget" category. The idea of a religion "upgrade" evokes the highly divisive concept of supersessionism among the major Abrahamic religions, which would be guaranteed to cause further outcry no matter which one of those the article would pick for the category. [A New York Times Wirecutter article. There is the NYT logo and Wirecutter logo in the top left. Also in the top of the page is a search bar, a user account icon, and 7 "header" level hyperlinks with illegible text. The article title is as follows:] The Best Religion By Wirecutter Staff [The words "Wirecutter Staff" are followed by illegible text presumably representing the date of the article. Below are icons for Twitter, Facebook, e-mail, and save.] [The article's image depicts Cueball shrugging in the center of the picture with many question marks floating above him. The content of the article is as follows:] What does it all mean? Our reviewers tried out over 70 of the most popular belief systems. Here's what they found…

Painbow Award

Painbow Award

https://www.xkcd.com/2537

https://www.explainxkcd.com/wiki/index.php/2537:_Painbow_Award

[A figure of a graph is shown, the figure has a number as if used in a paper. The graph has two labeled axis but without any units given. The Y-Axis has 15 ticks of equal length, the X-axis has 21 ticks, with every fifth double the height of the other. The graph displays a messy shape with color gradients, with a bright spot to the right of the shape around the middle right part of the graph. This bright spot is surrounded by mainly green and red, with darker colors at the edge, and the rest of the graph white. On the right side of the graph there is a labeled bar with the color scale. To the right of this are numbers indicating what the color represents. The color scale begins at the bottom with white, then goes to gray/blue, to black, back to blue, to gray, to green, to dark red, to red which fades via brown in to green, from where it fades slowly from darker green to lighter green ending up as yellow before going back to white again at the top.] Label: Figure 2 Y-Axis: λ X-Axis: θ (phase) Scale label: Peak Energy 120 100 80 60 40 20 0 [Caption under the panel:] Every year, disgruntled scientists compete for the Painbow Award for worst color scale.

This comic makes fun of the badly selected color scales used in the figures for scientific papers by suggesting that the scientists picking them are in competition to use the most problematic scale. The title of the comic is a portmanteau of "pain" and "rainbow" suggesting a humorous name for terrible color scales. The color scale here showcases a collection of unintuitive and unhelpful decisions. Starting from the top, white fades down into green, which then fades into red (passing through brown in the middle instead of yellow, indicating subtractive color mixing instead of additive color mixing, for no obvious reason). The red then turns back into green as the intensity decreases further. Red and green in close proximity make the energy levels hard or impossible to distinguish for those with protanopic color vision deficiency . This confusion is repeated at lower energy levels, where blue transitions to black and then back into white via a gray with a tiny tinge of blue. The highest and lowest recorded energy levels have the same color value, which is less than ideal. That Randall is aware of color blindness and the problems this causes has been revealed in other comics like this one 1213: Combination Vision Test . Although it's possible (for someone with full color vision) to interpret data from this graph from context clues - the white that fades to green is high-energy white, while the white that fades to blue is low-energy white - there's no benefit to doing things this way, and a lot of downsides. Additionally, there are regions in the color scale where the color changes very rapidly, which creates the false appearance of an edge in what is likely a smooth function. Because the color scale includes black, representing just over 20 unlabeled units, it is possible that the graph axes, labels, and perhaps even the comic's caption represent measured values. Because they don't blend continuously with the negative space around them, this appears unlikely. Real-world analogues to the Painbow Award include radar meteorology charts, where different types of precipitation have different color schemes that can overlap and blend in confusing transition zones. In the field of data visualization, the CIELAB color space , perceptually uniform color spaces , or even more specialised scales have been developed to replace simple algebraic interpolation of red, green, and blue values. The title text takes the concept of bad color combinations further, suggesting the use of navy blue , dark blue , and midnight blue for first, second, and third respectively. These are the names of three similar XKCD colors , and, as sighted readers will be able to see, there is very little difference between them [ citation needed ] . However, the choice of blue(s) may be a direct play upon the association of the Blue Riband (a.k.a. "Blue Ribbon") and/or Cordon Bleu (likewise, but this time direct from the French) awards, extended in common use for excellence across a much wider range of competitive fields. For rosette-rewarded competitions (e.g. livestock parades, dog-shows, etc) the first prize ones are commonly blue (red for 2 nd and either yellow or white for 3 rd ), though it may not be logically obvious to someone unfamiliar with this, perhaps more used to yellow depicting the 'gold standard, first place' indicator or red as the most alerting hue in some other ranking situations. Where a depicted award schema is directly gold/silver/bronze-influenced, however, the gold and bronze 'metallic off-yellows' can sometimes be more confused with each other than with the mid-level desaturated 'silver' [A figure of a graph is shown, the figure has a number as if used in a paper. The graph has two labeled axis but without any units given. The Y-Axis has 15 ticks of equal length, the X-axis has 21 ticks, with every fifth double the height of the other. The graph displays a messy shape with color gradients, with a bright spot to the right of the shape around the middle right part of the graph. This bright spot is surrounded by mainly green and red, with darker colors at the edge, and the rest of the graph white. On the right side of the graph there is a labeled bar with the color scale. To the right of this are numbers indicating what the color represents. The color scale begins at the bottom with white, then goes to gray/blue, to black, back to blue, to gray, to green, to dark red, to red which fades via brown in to green, from where it fades slowly from darker green to lighter green ending up as yellow before going back to white again at the top.] Label: Figure 2 Y-Axis: λ X-Axis: θ (phase) Scale label: Peak Energy 120 100 80 60 40 20 0 [Caption under the panel:] Every year, disgruntled scientists compete for the Painbow Award for worst color scale.

Snack

Snack

https://www.xkcd.com/2538

https://www.explainxkcd.com/wiki/index.php/2538:_Snack

[Ponytail, holding a cookie up in one hand and an apple up in the other, addresses an alarmed Cueball. His alarm is shown by seven lines radiating away from his head, and he also holds his arms stretched out.] Ponytail: Hey, do you want a cookie? Or an apple? Cueball: Who are you!? Did the IRB approve this!? Is everyone here an actor!? [Caption beneath the panel:] The best prank you can play on psych majors is just to offer them a snack.

Many psychological studies involve participants being asked to make decisions under varying conditions, to determine how those conditions influence decision making. A common example is to give subjects a choice between eating a healthy snack (such as an apple) or a tasty snack (such as a cookie), which may be used as a simple proxy for whether they're prioritizing long-term health or short-term gratification. In most cases they are not made aware of the nature of the experiment, as knowing the premise of the study is liable to influence their behavior and alter the results. Instead subjects may deliberately be given a false impression of the purpose of the study, or they may be offered a choice under conditions where they're not aware that they're part of an experiment at all. Examples of experiments like this are the Stanford marshmallow experiment and this study . This sort of psychological study is most commonly done by universities, which means that using university students as subjects is generally the most convenient option. This means both that psychological studies tend to be heavily skewed towards the demographics of college students, and that university students have a pretty good chance of being invited to participate in a study at some point. The joke in this strip is based on the premise that psychology majors are sufficiently aware of such studies that it would make them suspicious of any circumstances which could be part of a study. If they've studied (or even conducted) such experiments, anything that reminded them of such a study could cause them to become suspicious. In Cueball 's case this is exaggerated into outright paranoia, and Ponytail is apparently playing on that to prank him, offering options that could easily be part of such an experiment just to spook him into suspicion. Studies done on humans are subject to important ethical controls, particularly if the subjects are not fully informed of the study's purpose. "IRB" stands for Institutional Review Board , which is a committee (for example, at a university) which must approve such research to ensure that there's no significant risk of doing harm to the subjects of the study. The title text jokes that graduate students have so much work to do that they are liable to forget to eat entirely and stereotypically too impoverished to afford adequate amounts of food; when presented with an offer of a snack, they don't ponder the implications or potential ulterior motives; they just eat it quickly and get back to work. [Ponytail, holding a cookie up in one hand and an apple up in the other, addresses an alarmed Cueball. His alarm is shown by seven lines radiating away from his head, and he also holds his arms stretched out.] Ponytail: Hey, do you want a cookie? Or an apple? Cueball: Who are you!? Did the IRB approve this!? Is everyone here an actor!? [Caption beneath the panel:] The best prank you can play on psych majors is just to offer them a snack.

Flinch

Flinch

https://www.xkcd.com/2539

https://www.explainxkcd.com/wiki/index.php/2539:_Flinch

[Cueball holds a bowling ball in both hands. It is attached to a string that goes behind him and up disappearing off panel around double his height. He is talking to Megan, Hairy, and Ponytail who is looking at him. Between Cueball and the other three is a cross in a dotted circle on the floor.] Cueball: If you stand with the bowling ball in front of your face and let go, will you flinch when it swings back? [Zoom in on Megan in a slim panel. There is a caption in a frame above her.] Caption: Physicist Megan: I won't flinch. Megan: I trust conservation of energy. [Zoom in on Hairy, in a wide panel. He has lifted arm holding his hand palm up toward Cueball (who is off-panel). There is a caption in a frame above him.] Caption: Biologist Hairy: I trust my flinch reflex, which was honed by millions of years of evolution to protect my delicate face. I'm not messing with it. [Zoom in on Ponytail in a slim panel. There is a caption in a frame above her.] Caption: Engineer Ponytail: I don't trust that you hung that thing up correctly.

Cueball is performing a common physics demonstration in which a heavy ball is hung from a rope or cable. The demonstrator, or a volunteer, pulls the ball back until it's close to their face (possibly even touching it), then releases it, allowing it to swing, and then return. Due to conservation of energy, the ball cannot return any further than its original release point, making it impossible for the person to be struck by it. Because a heavy pendulum will tend to lose little energy on each swing (relative to its overall energy), it will come back very close to its original point, so the experiment creates a conflict between the instinctive desire to escape a heavy object flying at your face, and the theoretical knowledge that it won't harm you. Megan is a physicist, who understands the principles of the experiment and claims she won't flinch, confident that it can't harm her. Hairy is a biologist, and implies that he has no intention of avoiding the flinch reflex, as he trusts the automatic reflexes that the human body has evolved more than he trusts the premise of the experiment. In both 755: Interdisciplinary and 1670: Laws of Physics , the same experiment is referenced. In the title text of the latter Randall makes a very similar argument as the biologist does here. Ponytail , an engineer, replies that she doesn't trust Cueball to have hung the pendulum correctly. Engineers are trained in science, but work with practical applications, and tend to be very aware that practice is rarely as simple as scientific theories might imply. Even if the physical laws are constant, the experiment might not go according to plan. For example, if the cable were to snap or come loose while swinging toward the subject, the ball could strike them in the body, or land on their feet. If the cable is more elastic than anticipated, it could stretch unpredictably, once again striking someone. If the anchor point is not stable, it could shift during the experiment, once again causing harm. Also if the ball is not released but pushed, or if the one releasing it leans forward after release they might get hit in the face. The punch line basically makes the point that failure to trust the safety of an experiment doesn't necessarily imply a lack of scientific knowledge. If you lack confidence in the design of an experiment, then it's not safe to assume that the laws of physics will protect you. The title text shows a pre-med student's response. Pre-medical university courses have a reputation for being more intense and demanding than other undergraduate degrees, so the student is portrayed as being very stressed and time-conscious; showing little interest in the experiment itself, only in how it impacts their degree. In addition, medical students are commonly the subject of "interesting" medical experiments which may lead to long-term psychological and physical side-effects. The student first asks if participating in the demonstration will count for a physics credit, implying that they're not willing to spend time on it unless it contributes to their academic requirements. They then ask if they can shorten the string to make the demonstration go faster. Shortening a pendulum does, indeed, cause it to swing faster, but the time saved would be less than the time necessary to make the modification, so the demonstration would not end sooner. Finally, they ask to do a variant where they deliberately get struck in the face, because they have a "thing for first aid training" immediately after. This would likely injure them, but the student is apparently willing to sacrifice their own safety and well-being in service to their academic career. It's not clear how this would help, although it could potentially help others learn first aid by having them practice on the new injury. Various alternate takes on this experiment have been previously featured in 755: Interdisciplinary and 1670: Laws of Physics , but this is the first time experiment is performed in a proper manner. [Cueball holds a bowling ball in both hands. It is attached to a string that goes behind him and up disappearing off panel around double his height. He is talking to Megan, Hairy, and Ponytail who is looking at him. Between Cueball and the other three is a cross in a dotted circle on the floor.] Cueball: If you stand with the bowling ball in front of your face and let go, will you flinch when it swings back? [Zoom in on Megan in a slim panel. There is a caption in a frame above her.] Caption: Physicist Megan: I won't flinch. Megan: I trust conservation of energy. [Zoom in on Hairy, in a wide panel. He has lifted arm holding his hand palm up toward Cueball (who is off-panel). There is a caption in a frame above him.] Caption: Biologist Hairy: I trust my flinch reflex, which was honed by millions of years of evolution to protect my delicate face. I'm not messing with it. [Zoom in on Ponytail in a slim panel. There is a caption in a frame above her.] Caption: Engineer Ponytail: I don't trust that you hung that thing up correctly.

TTSLTSWBD

TTSLTSWBD

https://www.xkcd.com/2540

https://www.explainxkcd.com/wiki/index.php/2540:_TTSLTSWBD

[Cueball stands behind a lectern on a podium, gesturing with one hand held out, speaking to an audience. A banner hangs on the wall over the crowd with large letters on it. Illegible smaller text is written under these letters.] Cueball: Next we have a session on organ transplants and another on airships. Cueball: Then lunch, then we'll have one on gyroscopes and one on butterflies. Banner: TTSLTSWBD [Caption below panel:] The first annual conference on Things That Seem Like They Shouldn't Work But Do

Cueball is standing at a lectern on a podium , addressing a large crowd. He is describing the program of some event, listing the different topics that will be covered. These appear to be random, but the caption gives the punchline: it is a conference on things that seem like they shouldn't work but do. By "things that seem like they shouldn't work", it means things that the average person would have some intuitive sense that the function of thing was impossible, and yet ample real-world experience shows that they do, and may become a routine function that people depend upon. TTSLTSWBD in the title and the banner is the abbreviation for "Things That Seem Like They Shouldn't Work, But Do". Organ transplantation , where a functioning organ is cut out of one person (possibly a dead one) and put into another person where it will now operate for their benefit. Given the very complex and delicate nature of living tissue, it's rather surprising that this could work at all. In reality, it's not a simple process, and a lot of things could go wrong, but modern medicine is advanced enough that organ transplantation is widely accepted and regularly practiced, usually functioning well enough to extend life. Airships , or dirigibles, are huge , rigid structures which are filled with bags of lighter-than-air gas, which causes the entire structure to float, and could carry both passengers and significant loads. The idea of such a huge vessel traveling, able to both move rapidly and float in place, would be hard to imagine if it didn't exist, yet zeppelins functioned and were a practical mode of transportation for a time. Unlike the other things mentioned, airships are largely obsolete (having lost favor due to safety concerns and surpassed by other technologies). Airships are a recurring theme on xkcd. Lunch is listed as if it was another topic of the TTSLTSWBD, but it actually just means that after discussing airships, the conference will take a break to eat lunch, as many humans usually do. [ citation needed ] Because lunch is a relatively modern construction, filling a niche that grew after dinner shifted later into the day, it may defy one's intuition. In this sense, a three-meal day may seem like it shouldn't work, but most who observe all three meals on schedule would likely argue that it does. Mechanical gyroscopes are simple devices consisting of a spinning disc mounted inside three concentric gimbals as a fixture, or more often observed at work as a single spindle in a free-standing external frame that can be held or moved around by hand. The rotational inertia of the spinning disc resists change in orientation, and tends to remain in a single orientation (if free to do so) or else exert counter-intuitive forces (where directly encouraged to change its central axis). The notion that a disc can remain so steady can be counterintuitive even to those who understand the physical principles. This weirdness has been previously referenced in 332: Gyroscopes . An optical gyroscope does not mechanically resist any motion but (relying upon an effect originally exploited in a failed attempt to disprove Special Relativity ) ultimately provides similar feedback about the rotation of the unit into which it is mounted. Butterflies fly with an unusual fluttering pattern, which works in part due to the notoriously complex principles of fluid dynamics that may look like uncontrolled fluttering but yet somehow allows the creature to land directly on specific flowerheads to feed. This is not as intuitively understandable as the flight of larger creatures such as birds. The title text refers to rotary hooks on sewing machines, which are a complicated (and complicated looking) mechanism whose purpose is to feed one thread in a loop around a whole spool of another thread, and are apparently counterintuitive enough that the conference feels they need a whole day to cover them. This concept is referenced in 2115: Plutonium . The conference that the comic pictures is another example of a thing that seems like it shouldn't work but does. At first glance, Cueball seems to be listing a random, disconnected list of topics that will be covered, which runs counter to the format of most conferences. It initially seems inconceivable that enough people would be interested in all of those separate topics for the conference to make a profit (from attendance fees). However, the audience is packed, demonstrating that this is not the case. This may be because many people enjoy the mind-expanding feeling of having their intuitions shattered. [Cueball stands behind a lectern on a podium, gesturing with one hand held out, speaking to an audience. A banner hangs on the wall over the crowd with large letters on it. Illegible smaller text is written under these letters.] Cueball: Next we have a session on organ transplants and another on airships. Cueball: Then lunch, then we'll have one on gyroscopes and one on butterflies. Banner: TTSLTSWBD [Caption below panel:] The first annual conference on Things That Seem Like They Shouldn't Work But Do

Occam

Occam

https://www.xkcd.com/2541

https://www.explainxkcd.com/wiki/index.php/2541:_Occam

[Megan is holding a hand palm up towards Cueball as they are walking together.] Megan: The simplest explanation is that Occam shaves the barber.

This comic invokes three philosophical topics: Occam's Razor , the Barber Paradox and Murphy's Law . Occam's Razor is the principle that explanations should not postulate more entities than necessary. It is often phrased as "the simplest explanation is best". The word ' razor ' is intended to evoke the image of shaving off superfluous elements. The Barber Paradox postulates a town barber who shaves all those, and those only, in the town who don’t shave themselves, and asks whether the barber shaves himself. The paradox is that if he does, then he shouldn’t, and if he doesn’t, then he should. It is an attempt at a concrete, real-world analogue of Russell's Paradox in set theory. Megan tries to invoke Occam's Razor to create a simpler solution to the paradox. Occam's Razor is named in honor of philosopher William of Ockham (Ockham being a town in England) and she declares that William shaves the barber. Her proposal is humorous and does not of course resolve the paradox, as the barber is still not shaving himself (so he should shave himself, so he shouldn't shave himself...) The title text invokes Murphy's Law: the expectation that "anything that can go wrong will go wrong." When you shave with a cut-throat razor , there's multiple things that could go wrong , many of which would cause harm to the person being shaved. Alternatively, invoking Murphy's law makes the principle of Occam's Razor itself, or its use in the comic, "go wrong", possibly rendering the solution invalid. [Megan is holding a hand palm up towards Cueball as they are walking together.] Megan: The simplest explanation is that Occam shaves the barber.

Daylight Calendar

Daylight Calendar

https://www.xkcd.com/2542

https://www.explainxkcd.com/wiki/index.php/2542:_Daylight_Calendar

[Danish is looking down at her phone which she holds up in her hand, while Cueball stands next to her]: Danish: Ugh, I hate November. It's 26:15 and the sun is setting again! Danish: 3-day days are the worst. Cueball: I like it. I know it's dark, but it's nice to have the extra time on deadlines. [Caption below the panel]: In our new calendar system, the date changes after every 12 hours of daylight, regardless of how long that takes.

At the time of this posting, the United States had ended daylight saving time (DST) recently, on November 7, and returned to standard time. Daylight saving time is a practice of setting clocks ahead by 1 hour during warmer months to effectively 'borrow' some of the typically unused early morning light and pass it down to the late evening where more people can make use of it. In the United States, daylight saving time starts on the second Sunday in March and ends on the first Sunday in November. A result of ending of daylight saving time is the sun setting earlier than people are used to, as people have become acclimatised to the shifted clocks — though it does mean an 'extra' hour of light has returned to the seasonally redarkening mornings. The start of the comic may be the start of a typical comment about how the sun seems to set earlier than usual in November; which it does anyway (north of the equator) but the clock-shift makes it even more obvious. In this comic, however, Randall turns the normal talk about DST on its head by devising a calendar system where the dates "change" based on 12 hours of daylight. This causes shorter "days" in the summer months, which may get more than 12 hours of daylight in a "solar day" and longer "days" in the winter months which would have fewer hours of daylight in a "solar day". As mentioned in the title text, this change would be very pronounced near the poles, which may only get a few hours of daylight per 24 hours in the winter, but conversely may get 20 or more hours of daylight per 24 hours in the summer. Cueball says that he likes the new calendar system, as it gives him more "time" in the winter to complete work - if Cueball is given "3 days" to complete a task, each of those days could be longer than a typical 24 hours. However, this would be reversed in the summer, as each day would be shorter. Also, if this calendar system was in place, his boss could resolve this problem by just giving him 72 hours to complete his task instead of "3 days". At temperate latitudes and above, as the calendar goes towards winter (for your hemisphere) the length of daylight per daily cycle shortens. Instead of having "long summer days" (i.e. periods of daylight) and shorter ones in the winter, but still the artificial pressures of a regulated 24-hour cycle to adhere to, the proposal seems to be that the date gets incremented whenever (and only when) twelve hours of daylight have passed. In the summer, a day-count starting at sunrise could require a late-afternoon switch to 'tomorrow', which would in turn be switched earlier still the next day as it was already partly used up, with possibly two date-changes per astronomical day (early morning and mid-evening, for example). As winter draws on, not enough daylight will pass to guarantee a date-change in any single period. On the day of this comic's release - November 15, 2021 - Massachusetts, where Randall lives, gets ten hours and forty five minutes between civil twilights . It is possible that the last day-mark was late during the previous daylight cycle and the next one won't be until early in the following one. Depending on how exactly daylight is measured, we may have more "days" in a year than the usual 365, since refraction of light near the horizon means that the sun is visible slightly more than 50% of the year on average. This effect is strongest near the poles, since the sun spends more time near the horizon. In addition, due the Earth's elliptical orbit, more northerly parts of the Earth receive more sunlight than southerly parts. Combined, these effects mean that a year at the north pole is 381 "days", compared to 369 at the Equator. Exactly how the time is marked is not fully explained. Starting each day-period at 00:00 would be easiest, but could be a psychological step too far. One possibility is to set a nominal 00:00 six hours before a day-change, in line with an 'idealised' twelve-hours-of-daylight day, but disregard hours 'belonging' to a prior daylight period. Then keep the clock running (throughout any intervening nights and into the next daylight as necessary) until the date clicks over and realigns as necessary. Clock times would not reach 23:59 for most of the summer, and could far exceed that in the winter. Megan's clock has reached 26:15, by this sunset, and may well be due to be far into the 30-hours range before more daylight and the moving on to the new date and reset time, if not beyond. Beyond the arctic (and antarctic) circle, twelve hours of daylight would be accumulated up twice per traditional day, at times, while being effectively on hold for much of the other six months, depending upon actual latitude. [Danish is looking down at her phone which she holds up in her hand, while Cueball stands next to her]: Danish: Ugh, I hate November. It's 26:15 and the sun is setting again! Danish: 3-day days are the worst. Cueball: I like it. I know it's dark, but it's nice to have the extra time on deadlines. [Caption below the panel]: In our new calendar system, the date changes after every 12 hours of daylight, regardless of how long that takes.

Never Told Anyone

Never Told Anyone

https://www.xkcd.com/2543

https://www.explainxkcd.com/wiki/index.php/2543:_Never_Told_Anyone

[Megan and Cueball are holding hands, she has turned her head towards him, while he is still looking at the scenery. They are standing on the edge of a cliff, overlooking a vast stretch of land with water to the right and mountains far off. There are many details with lakes and smaller bodies of water on the land, three larger and three smaller clouds near the horizon and the sun is shining from the top right corner.] Megan: I've never told anyone this before. [Cueball has turned towards Megan, as they are still holding hands, in an otherwise empty panel.] Megan: I know I shouldn't. Megan: But I feel like I can trust you. [Megan and Cueball are no longer holding hands as he has taken both his hands up in front of his mouth and a sound escapes him, as shown with small lines coming off his head with the speech line going up from above them.] Megan: My one-time code is 263827. Cueball: *Gasp*

This comic combines stereotypes about two secrets that one would normally be reluctant to share: dark, personal secrets , and passwords . In the comic, Megan appears to be about to tell Cueball a secret of the former variety, but twists it by instead revealing a one-time code (presumably for the use of two-factor authentication for an online account). This is poking fun at the serious-looking warnings that typically accompany the generation of one-time codes. For example: "DO NOT share this code with anyone. We will NEVER call you to ask for it." While this is still something Megan should normally be reluctant to share, it has much less value to Cueball than a personal secret [ citation needed ] unless his intent was to steal Megan's account - and even then it's probably useless, as these codes become invalid after they're used (hence the term "one-time") or a few minutes after generation. Cueball compounds the humor by reacting with a shocked gasp, as one would be more expected to react to a dark secret. Users are generally warned never to tell their password to anyone, not even a support representative of the site; real technical support reps shouldn't ever need your password, and anyone with a true configured-in authority should never even find it necessary to know/use it. However, one tactic that hackers use to break into accounts is to claim to be calling from the site and say that they need your password to fix some vague and/or mythical problem with the account. The title text says that Megan trusts Cueball so much that, despite knowing this, she would divulge her password to him even if he tried this approach on her. There is a further irony here, as Megan is focusing on the exception to the rule ("Don't even tell an employee" implies "You shouldn't tell anyone ") as if it was the most important factor. [Megan and Cueball are holding hands, she has turned her head towards him, while he is still looking at the scenery. They are standing on the edge of a cliff, overlooking a vast stretch of land with water to the right and mountains far off. There are many details with lakes and smaller bodies of water on the land, three larger and three smaller clouds near the horizon and the sun is shining from the top right corner.] Megan: I've never told anyone this before. [Cueball has turned towards Megan, as they are still holding hands, in an otherwise empty panel.] Megan: I know I shouldn't. Megan: But I feel like I can trust you. [Megan and Cueball are no longer holding hands as he has taken both his hands up in front of his mouth and a sound escapes him, as shown with small lines coming off his head with the speech line going up from above them.] Megan: My one-time code is 263827. Cueball: *Gasp*

Heart-Stopping Texts

Heart-Stopping Texts

https://www.xkcd.com/2544

https://www.explainxkcd.com/wiki/index.php/2544:_Heart-Stopping_Texts

[Comic heading:] Most heart-stopping texts to receive out of the blue [A collection of light gray text bubbles in two columns:] Did you forget what day it is? I bet you're probably getting bombarded with texts right now, huh? Did you mean to post that to everyone? Is this your house? cnn.com/2021/11/19/S... You didn't click on any weird emails recently, did you? Can I call? Wait, do you know Joe Rogan? How does he know your name? Why are you trending on Twitter?

Text messages have become a ubiquitous form of communication in most countries, and have become a basic part of many people's everyday lives. Conversations over text frequently jump straight to the purpose of the communication, without salutation or prelude. Some texts, particularly when delivered without context, can carry implications that cause immediate anxiety. "Out of the blue" is an English expression meaning "to appear in a sudden and unexpected fashion". It's a shortened version of "sudden as a bolt out of the Blue", referring to a bolt of lightning out of the clear, blue sky. The implication is that something dramatic (and possibly dangerous) is has occurred without any warning signs, under circumstances where it wouldn't normally be expected. This comic lists texts that would be worrying to receive with no context, for a variety of reasons. It seems to suggest that sending these is a good way to prank someone; particularly the title text, where deliberately sending an animated loading icon seems like it couldn't be intended for any other purpose. The different messages are explained below. [Comic heading:] Most heart-stopping texts to receive out of the blue [A collection of light gray text bubbles in two columns:] Did you forget what day it is? I bet you're probably getting bombarded with texts right now, huh? Did you mean to post that to everyone? Is this your house? cnn.com/2021/11/19/S... You didn't click on any weird emails recently, did you? Can I call? Wait, do you know Joe Rogan? How does he know your name? Why are you trending on Twitter?

Bayes' Theorem

Bayes' Theorem

https://www.xkcd.com/2545

https://www.explainxkcd.com/wiki/index.php/2545:_Bayes%27_Theorem

[Miss Lenhart is pointing with a pointer, held in her right hand, to a white-board with tables, what looks like formulae and lots of other unreadable text. She looks toward her off-panel class, from where a voice replies to her question.] Miss Lenhart: Given these prevalences, is it likely that the test result is a false positive? Off-panel voice: Well, this chapter is on Bayes' Theorem, so yes. [Caption below the panel]: Sometimes, if you understand Bayes' Theorem well enough, you don't need it.

For example, if a test has a 100% sensitivity (first line, all those affected receive a positive result) and a 99% specificity (second line, 1% of the unaffected also receive a positive result), the interpretation of a positive test depends on the prevalence of the disease in the population. In the example case, the prevalence is 0.1% (third column), so that when the test result is positive (1% of the tests, left column) the subject is actually unaffected nine time out of ten. Although this would be a very performant test, given the relative prevalences involved it will produce overwhelmingly false positives among all positive results. (But, in this example, all those told they are not in danger — almost a hundred times more individuals than test positive — are correctly notified.) For this same example, the Bayesian formula gives : P( Affected | Positive ) = P( Positive | Affected ) * P( Affected ) / P( Positive ) = 100% * 0.1% / 1% = 10% and P( Unaffected | Positive ) = P( Positive | Unaffected ) * P( Unaffected ) / P( Positive ) = 0.9009% * 99.9% / 1% = 90% In this comic, a teacher is presenting a problem which the students are supposed to use Bayes' theorem to solve. However, the off-panel student knows that they are studying Bayes' theorem, so they use that prior knowledge to guess the usual answer to such problems. The punch line is the caption - The student doesn't need to do the calculation because they're familiar with questions involving Bayes' theorem and how they often present the counterintuitive result to illustrate the importance of prevalence to the calculation. There is perhaps also a self-referential situation here where the student has updated their prior probabilities a number of times for whether the answer was "Yes" to a question involving Bayes' Theorem. If their method of answering "Yes" to every such question has succeeded every time before then by Bayes' theorem they will have a lot of justification to continue to do until they start getting it wrong. The prevalence of Bayes Theorem questions that require the answer "No" might be small enough that this doesn't happen in any small number of times and so they learn nothing of the false-positive rate until that point in time. This could be interpreted as a criticism of Bayesian Statistics which may treat a judgement as well justified (e.g. getting the question right) despite lacking a clear understanding of mechanism (e.g. basing your answer to the question on the numbers provided). The title text refers to the mathematical definition of Bayes' theorem: P(A | B) = P(B|A) * P(A) / P(B). Here, P(A|B) represents the probability of some event A occurring, given that B has occurred. This is often referred to as "the probability of A given B". It can be hard to remember if P(A|B) means probability of A given B, or if it's B given A, especially when talking about the probability of an earlier cause given a later effect. Randall's joke is based on this difficulty. Here P((B|A)|(A|B)) is meant to be read as the probability that you write (B|A) given that the correct expression is (A|B), which makes it the probability that you got the order of the notation mixed up. [Miss Lenhart is pointing with a pointer, held in her right hand, to a white-board with tables, what looks like formulae and lots of other unreadable text. She looks toward her off-panel class, from where a voice replies to her question.] Miss Lenhart: Given these prevalences, is it likely that the test result is a false positive? Off-panel voice: Well, this chapter is on Bayes' Theorem, so yes. [Caption below the panel]: Sometimes, if you understand Bayes' Theorem well enough, you don't need it.

Fiction vs Nonfiction

Fiction vs Nonfiction

https://www.xkcd.com/2546

https://www.explainxkcd.com/wiki/index.php/2546:_Fiction_vs_Nonfiction

[Cueball is talking to Ponytail and White Hat.] Cueball: Star Wars ? Ponytail: Fiction. [Same setting.] Cueball: The Making of Star Wars ? White Hat: Nonfiction. [Closeup of Cueball.] Cueball: Star Wars: The Adventures of Boba Fett ? Off-panel voice: Fiction. [Closeup of Ponytail.] Cueball (off-panel): Star Wars: The Official Guide to Boba Fett's Armor and Weapons ? Ponytail: Nonfiction, technically. [Cueball has lifted a hand palm up as he talks to Ponytail and White Hat.] Cueball: Boba Fett's Gadgets and How He Got Them ? Ponytail: ...Fiction? Ponytail: It depends. [Cueball is talking to Ponytail and White Hat. Ponytail has turned towards White Hat and has taken a hand to her chin.] Cueball: Boba Fett: A Life , by historian Doris Kearns Goodwin? Ponytail: Hm. White Hat: Maybe we should just have a Boba Fett section.

Cueball is asking Ponytail and White Hat to classify different Star Wars books and movies as fiction or nonfiction. (Perhaps he is working at a library or bookstore, or sorting a personal collection.) Star Wars as a whole is a multimedia franchise, which includes films, TV series, novels, etc, but often singularly refers to the original 1977 film later more lengthily titled Star Wars: Episode IV – A New Hope (or, given the fact that the rest of the titles are books, one of several novelizations based on the script). The classifications get more complicated to determine as the conversation progresses while revealing a quite specific obsession with the character of Boba Fett . The complexity may even end up converting lumpers into splitters , a philosophical distinction that another recent comic touched upon. Nonfiction (also spelled non-fiction) is any document or media content that intends, in good faith, to present only truth and accuracy regarding information, events, or people. In contrast, fiction offers information, events, or characters expected to be partly or largely imaginary, or else leaves open if and how the work refers to reality. In the end, White Hat suggests that, since Cueball has so many works featuring Boba Fett, it would be more useful to group them together in a new category rather than sorting them into the fiction and nonfiction sections. [Cueball is talking to Ponytail and White Hat.] Cueball: Star Wars ? Ponytail: Fiction. [Same setting.] Cueball: The Making of Star Wars ? White Hat: Nonfiction. [Closeup of Cueball.] Cueball: Star Wars: The Adventures of Boba Fett ? Off-panel voice: Fiction. [Closeup of Ponytail.] Cueball (off-panel): Star Wars: The Official Guide to Boba Fett's Armor and Weapons ? Ponytail: Nonfiction, technically. [Cueball has lifted a hand palm up as he talks to Ponytail and White Hat.] Cueball: Boba Fett's Gadgets and How He Got Them ? Ponytail: ...Fiction? Ponytail: It depends. [Cueball is talking to Ponytail and White Hat. Ponytail has turned towards White Hat and has taken a hand to her chin.] Cueball: Boba Fett: A Life , by historian Doris Kearns Goodwin? Ponytail: Hm. White Hat: Maybe we should just have a Boba Fett section.

Siren

Siren

https://www.xkcd.com/2547

https://www.explainxkcd.com/wiki/index.php/2547:_Siren

[Circe is speaking to Odysseus.] Circe: Remember, Odysseus: Circe: As you pass the rocks you will hear a woman calling out to you, urging you to stray from your path, but plug your ears and hold your course, for her beguiling lies will draw you to a watery grave. Circe: I don't know why they can't just fix it. I keep filing error reports. [Caption below the panel:] Circe was actually just telling Odysseus to ignore his GPS.

Odysseus is the hero of the Greek epic Odyssey by Homer . This is a poem that relates the journey of Odysseus back home to his homeland from the newly defeated Troy, and how he inadvertently angered Poseidon thus causing the journey to take 10 years. In the story, now widely translated and adapted for modern audiences, Circe warns Odysseus of the Sirens , who sing beautiful songs that lure sailors towards their shores, just to doom the boats to sink upon the jagged rocks surrounding their islands. In Odysseus's own case, the Sirens even claim to be able to " tell you everything that is going to happen over the whole world "; at this point, Odysseus has been away from home for many years and has no idea if his wife and son remember him, so the temptation to stay and listen (and thus find out if he will be able to return alive) is especially powerful. This comic reframes the advice as if Odysseus was being told to ignore the incorrect instructions of a GPS-linked routefinder , rather than the Sirens. Errors, omissions or out-of-date information in the databases used by such devices famously have sent drivers down roads they might never have even tried to use (guided by printed maps, road-signs or even past experience) without the alluring voice of the 'infallible' dashboard device leading them through too-narrow lanes, into rivers or even hundreds of miles completely out of their way - perhaps to a destination similarly-named to their intended one. GPSs did not exist during the time the poem was written, [ citation needed ] so this could not be the case here. A navigation system giving wrong directions can happen, for example, due to outdated or incomplete map data. Sometimes users can file an error report with the provider of the navigation system and hope that they fix the problem in a software update. This is what Circe already did multiple times. However, the error was not fixed, so she has to resort to telling Odysseus to ignore the route. The title text shows what the route description could have looked like, had Odysseus indeed used a modern navigation system. It includes the start and destination of the route, the estimated duration and warnings about special circumstances of the journey. Normally, the sea voyage from the City of Troy to Ithaca should take much less than ten years. For Odysseus it took so long because of the many obstacles he had to face, so the navigation system would have some sort of clairvoyance function built in. "Route crosses an international border" and "Route includes a ferry" are standard warnings included in a route description. The former alludes to the facts that Odysseus's voyage took him to many lands and kingdoms while the latter may allude to the fact that in Book XI of the Odyssey, Odysseus visits Hades, which is traditionally reached by a ferry across the river Styx, piloted by Charon the ferryman. "Route includes capture by the goddess Calypso " is not normally something that a navigation system would warn about or could know about, [ citation needed ] but this indeed happened to Odysseus in Homer's tale; he was kept on her island Ogygia for seven years. The weird directions in the title text may be a reference to 461: Google Maps . [Circe is speaking to Odysseus.] Circe: Remember, Odysseus: Circe: As you pass the rocks you will hear a woman calling out to you, urging you to stray from your path, but plug your ears and hold your course, for her beguiling lies will draw you to a watery grave. Circe: I don't know why they can't just fix it. I keep filing error reports. [Caption below the panel:] Circe was actually just telling Odysseus to ignore his GPS.

Awful People

Awful People

https://www.xkcd.com/2548

https://www.explainxkcd.com/wiki/index.php/2548:_Awful_People

[Cueball and Megan are having a conversation while walking.] Cueball: The Internet makes it easy to be a jerk and forget the person we're talking to is a human. Megan: Yeah... Megan: But it also makes us see messages from awful people and assume they come from normal peers. [Closeup on Megan. Above Megan is a picture of a "reply" post from a man with sunglasses. The post has a title above it.] Megan: Recently I got a mean reply from a stranger. It was minor but it really got to me. Post title: Replies to "Favorite Movie" Post: Every group has one person who likes that movie, and it's the friend they all secretly hate. [Blondie as a news anchor behind a desk. A "News4" logo is displayed on the desk. There is a picture of the man with sunglasses with "Arrested" under his name. His picture is next to a picture of a house with "Breaking" above it. Megan's dialogue appears above the picture, but she herself is not shown in this panel.] Megan: Then the next week I saw that guy on the news. He was an actual murderer! [Megan and Cueball standing next to each other.] Megan: I can't believe I spent a week stressed out that my taste in movies wasn't shared by the East Valley Strangler. Cueball: Yeah, at least wait for a second opinion from the Lake Slayer.

Megan and Cueball are having a conversation about social media. Cueball mentions that when responding to textual comments on a screen, it can be easy to forget these comments are made by thinking, feeling humans (a sentiment expressed before on XKCD ). Megan agrees, but also relates a negative comment she got from a stranger about her taste in movies. The twist is that it turns out the person criticizing her was a murderer. Although this does not inherently negate his taste in movies, it does free Megan from the burden of weighing his opinions equally to her own. The title-text mentions the “LakeSlayer7” which is clearly a reference to the "Lake Slayer" in the comic. They mention, contrary to several other reviewers, that a burger joint in town is unsatisfactory, and that the reader should come to a place “by the lake” instead, which might be (and probably is) a plot to lure people to the lake and to be slain. [ citation needed ] In many social and news sites there is a tendency to surface negative content . This can be editorial intent , naive algorithms , or both , attempting to induce rage to drive engagement. Review sites can exhibit a bias in either direction, with minutiae burying valid feedback. [Cueball and Megan are having a conversation while walking.] Cueball: The Internet makes it easy to be a jerk and forget the person we're talking to is a human. Megan: Yeah... Megan: But it also makes us see messages from awful people and assume they come from normal peers. [Closeup on Megan. Above Megan is a picture of a "reply" post from a man with sunglasses. The post has a title above it.] Megan: Recently I got a mean reply from a stranger. It was minor but it really got to me. Post title: Replies to "Favorite Movie" Post: Every group has one person who likes that movie, and it's the friend they all secretly hate. [Blondie as a news anchor behind a desk. A "News4" logo is displayed on the desk. There is a picture of the man with sunglasses with "Arrested" under his name. His picture is next to a picture of a house with "Breaking" above it. Megan's dialogue appears above the picture, but she herself is not shown in this panel.] Megan: Then the next week I saw that guy on the news. He was an actual murderer! [Megan and Cueball standing next to each other.] Megan: I can't believe I spent a week stressed out that my taste in movies wasn't shared by the East Valley Strangler. Cueball: Yeah, at least wait for a second opinion from the Lake Slayer.

Edge Cake

Edge Cake

https://www.xkcd.com/2549

https://www.explainxkcd.com/wiki/index.php/2549:_Edge_Cake

[Megan is walking towards Cueball and Emily (who resembles Hairbun), holding a cake.] Megan: Happy birthday, Emily! Cueball: Wait, wasn't that last month? When's your birthday, anyway? Emily: It's complicated. [A diagram of a flight path over the North Pole, with meridian lines radiating out from the center. Emily's dialogue appears above the diagram, but she herself does not appear in this panel.] Emily: My mom went into labor on an arctic international flight that diverted directly over the North Pole. Emily: I was born in every time zone at once. [With Megan standing behind her, Emily holds out a plate of cake to Cueball.] Emily: It was also February 29th, and the airline was just changing ownership between countries. Emily: The International Bureau of Weights and Measures finally issued a declaration that it's my birthday whenever I want. Emily: Cake? Cueball: Nice, it's all edge pieces.

Megan —possibly an IERS (International Earth Rotation and Reference Systems) agent—wishes Emily, represented as Hairbun , Happy Birthday. This prompts a confused Cueball to ask if her birthday was sometime last month. Emily explains that she was born over the North Pole in a plane, meaning that she was born in every timezone at once. Technically though this is false, as there are some timezones (such as UTC+5:45 ) that are not represented at the north pole. Except for the one hour before it's midnight at the International Date Line, the date in eastern time zones is one day ahead of western time zones, so Emily would have been born on two days at once. She also says that it was February 29th (presumably it was also February 28 or March 1 in some time zones). February 29th only happens at most once every four years in the Gregorian calendar, adding to the confusion - people born on February 29th often celebrate their non-leap-year birthdays on arbitrary days (or not at all ). Normally one could simply use the time zone of the city the airplane took off from , but the airline company was changing ownership from one country to another at the time, so this option has apparently been ruled out. This is not terribly logical, however, since contracts transferring ownership usually specify an exact time (commonly one minute before or after midnight in a specific time zone to avoid confusion on which day midnight is in) to come into effect. Regardless of which time zone(s) she was in when she was born this is an absolute time and if she was born before it she would have been born in an aircraft of the first country and if after it in an aircraft of the second country. Alternately, the time zone of the city the aircraft took off from doesn't change even if the nationality of the plane changes in midair, so that should have still been an option. The punchline is that rather than try to identify the correct birthday for Emily, the BIPM has decided to let her have birthdays whenever she wants. This doesn't make much sense, however. As noted above even if she was born in every time zone at once it could only have been on one of two days (February 29th, plus either February 28th or March 1st). Since it is common for people born on February 29th to celebrate on February 28th in non-leap years, it would have been trivial to pick the non-leap day present in some of the time zones (either February 28th or March 1st) and declare it Emily's birthday. It's possible that Emily was told "You can choose when you want your birthday to be", and Emily decided to exploit the lack of specificity to the degree presented in the comic. In real life researchers in the Arctic at or near the North Pole use Coordinated Universal Time as the local time standard by convention, to avoid this exact problem. Thus it could have been said that Emily was born on the date that it was at that time in UTC. Furthermore, it is extremely unlikely that she would have been born at the exact instant the plane was over the north pole, indeed, it is unlikely that the plane even traveled over the exact pole, as opposed to a few miles or even feet to either side of it. With modern positioning equipment such as GPS, it should have been possible to determine which time zone the plane was in when she was born. Even in the impossibly unlikely event that she was directly above the pole at the instant of her birth, at jetliner speeds the plane was traveling about ten miles per minute, so a reasonable delay of even seconds in declaring "time of birth" would have placed the plane and her clearly in one time zone. Both the comic title and Cueball's final line are puns on " edge case ", an engineering term referring to situations or conditions that are unusual in a way likely to cause problems unless specifically accounted for. Edge pieces are generally only important with sheet goods (brownies, sheet cakes, etc), which are typically cut into pieces creating a difference between pieces originating on the edge and pieces originating from the center. Since the top and sides of a cake are often frosted, an edge piece has two faces covered in frosting and a corner piece has three, while a center piece only has one. Depending upon your relative preferences between the surface (often icing over marzipan) and core body of the cake (which can be fruitcake, or some variety of spongecake, etc, but not actually obvious which until the cake is cut), it being an edge-faced slice can be considered a bonus. Cueball certainly seems to appreciate this. The title text states that the IERS sends Emily a cake every time they add or remove a leap second, out of superstition (perhaps Megan is delivering that cake). The International Earth Rotation and Reference Systems Service is in charge of global time standards. It occasionally adds one leap-second to Coordinated Universal Time to adjust for changes in the rotation speed of the Earth. The comic might also be a modern version of the SS Warrimoo , a passenger liner that reportedly crossed the international date line at the equator on midnight Dec. 31, 1899. This would have placed her bow in the Southern Hemisphere on 1 January 1900, her stern in the Northern Hemisphere on 31 December 1899. She would therefore have been simultaneously in two different hemispheres, on two different days, in two different months, in two different years, in two different decades, and according to some definitions in two different seasons (northern winter and southern summer) and possibly in two different centuries. [Megan is walking towards Cueball and Emily (who resembles Hairbun), holding a cake.] Megan: Happy birthday, Emily! Cueball: Wait, wasn't that last month? When's your birthday, anyway? Emily: It's complicated. [A diagram of a flight path over the North Pole, with meridian lines radiating out from the center. Emily's dialogue appears above the diagram, but she herself does not appear in this panel.] Emily: My mom went into labor on an arctic international flight that diverted directly over the North Pole. Emily: I was born in every time zone at once. [With Megan standing behind her, Emily holds out a plate of cake to Cueball.] Emily: It was also February 29th, and the airline was just changing ownership between countries. Emily: The International Bureau of Weights and Measures finally issued a declaration that it's my birthday whenever I want. Emily: Cake? Cueball: Nice, it's all edge pieces.

Webb

Webb

https://www.xkcd.com/2550

https://www.explainxkcd.com/wiki/index.php/2550:_Webb

[Cueball and Ponytail are looking at an advent calendar hanging on a wall in front of them. The advent calendar is loosely tiled with 18 smaller hexagons, numbered from 5 to 22 in no clear order or pattern. They are regularly arranged into a larger hexagonal shape and of the five rows, there are three in the top and bottom ones, as also with each diagonal edge. There are four in each of the other rows, offset symmetrically, with a gap where a fifth could have been in the centre of the middle row.] Cueball: The hexagons are nice. Cueball: But why does it end at 22? Numbers: [Caption below the panel:] Astronomer Advent Calendar

This comic depicts an advent calendar geared toward astronomers anticipating the launch of the James Webb Space Telescope . At the time this comic was published, the James Webb Space Telescope (JWST) was scheduled to be launched on the 22nd of December, 2021 (after many prior delays ). Christmas would indeed have come early for astronomers if the launch had been successful and on time. By December 14, the launch date had been pushed back again to "no earlier than December 24", as NASA was working on resolving a communications issue between the observatory and its launch vehicle system. This was followed by another delay announced on December 21, when the launch date was pushed back to December 25, due to weather concerns. It was successfully launched from Kourou in French Guiana on December 25 at 09:20 FGT (12:20 UTC, 07:20 EST ), as hoped for in this comic: 2559: December 25th Launch . A normal advent calendar marks the days until Christmas by allowing miniature doors to be opened, or other means of revealing some treat/picture. This is often from the 1st of the month until the 'big reveal' on the 24th or 25th, though other schemes may exist in other cultures. This particular calendar features 18 hexagonal features, intended to be sequentially accessed over several days, in the same layout as the 18 gold-beryllium mirror segments designed to fold out to form the JWST's primary mirror. The first door is on the 5th, two days after this comic's publication date, making the last on the 22nd, the 'Big Day'. Cueball's question could be interpreted two ways: Cueball doesn't know about JWST, so he is asking why this advent calendar ends before Christmas (and possibly fearing this calendar is similar to the one in 1245: 10-Day Forecast ); or Cueball does know about JWST and its history of delays, so he is asking why the calendar ends on 22 when there is no certainty in that launch date (and also implying that he expects it to be delayed). [Note: two weeks after the comic was posted, the JWST was again delayed, this time to no earlier than Christmas Eve (and later finally to Christmas Day itself), making the expectation accurate. This would also make a traditional advent calendar serve equally well, were it not for the hexagon design.] December 22 is also the day after the northern hemisphere winter solstice. The end of the world was famously predicted for the winter solstice in 2012 . The title text references the fact that chocolates in advent calendars are often molded into different shapes, and the fact that the later numbers have a "pamphlet on managing anxiety" is probably supposed to quell the impeding fear that the launch could be delayed further or go wrong. The telescope's launch was initially planned for 2007, but due to various redesigns, financial issues, accidents, flaws, and the COVID-19 pandemic , the launch date was pushed back to 2011, then 2013, 2018, 2020, May 2021, October 2021, and finally to the current launch date in December 2021. It may also allude to post-launch concerns; even if the launch goes well, there will still be nervousness about the complex 160-day process in which the JWST reaches its intended observation point 930,000 miles from Earth, many subsystems are unfolded/deployed, and the instrument passes its final calibrations. There is effectively no way to rescue/repair this expensive piece of equipment should anything be amiss, unlike the Hubble Space Telescope , which was visited five times by Space Shuttles to remedy and enhance various features. (There exist issues with even Hubble that cannot currently be considered repairable without the Shuttles or any proven replacement, and the JWST will be located far beyond Hubble's operational orbit in a place much more difficult to get to.) The JWST has been referenced previously in 1730: Starshade , 2014: JWST Delays and 2447: Hammer Incident , mentioned in 1461: Payloads as well as indirectly in 975: Occulting Telescope . After this comic it was referenced in 2559: December 25th Launch and 2564: Sunshield . [Cueball and Ponytail are looking at an advent calendar hanging on a wall in front of them. The advent calendar is loosely tiled with 18 smaller hexagons, numbered from 5 to 22 in no clear order or pattern. They are regularly arranged into a larger hexagonal shape and of the five rows, there are three in the top and bottom ones, as also with each diagonal edge. There are four in each of the other rows, offset symmetrically, with a gap where a fifth could have been in the centre of the middle row.] Cueball: The hexagons are nice. Cueball: But why does it end at 22? Numbers: [Caption below the panel:] Astronomer Advent Calendar

Debunking

Debunking

https://www.xkcd.com/2551

https://www.explainxkcd.com/wiki/index.php/2551:_Debunking

[Several news headlines are shown in boxes.] [Box 1] AP photos show Dr. Fauci's office contains a normal number of microwaves [Box 2] Fact check: singer Billie Eilish was born years after the TWA Flight 800 explosion [Box 3] Vaccinated people can remove their hats without trouble by tugging upward, say doctors [Box 4] Physicists say Dorito powder is affected by gravity [Box 5] Steering wheels will work normally on Dec 12th; make left and right turns as usual [Box 6] CNN investigation: Santa's skin is dry and healthy this year, with the same amount of oil as before [Caption below the panel:] I don't know whether the "Don't repeat the claim in the headline debunking it" thing works or not, but it definitely makes reading the news weird.

When writing a news article that "debunks" a claim (shows why it is false), writing its headline in the form "X is false" is discouraged . The reason is that just repeatedly seeing "X", even if negated or followed by "is false", can make readers subconsciously believe it. To avoid this, Randall as a journalist has worded his debunking articles in a positive sense. This makes for a confusing read if the reader has not heard of the original claim. The "original claims" allegedly being debunked here don't actually appear to have been made anywhere, and can only be inferred from the debunking. Much of the debunking relies on setting simple facts straight, making for bizarrely banal headlines. [Several news headlines are shown in boxes.] [Box 1] AP photos show Dr. Fauci's office contains a normal number of microwaves [Box 2] Fact check: singer Billie Eilish was born years after the TWA Flight 800 explosion [Box 3] Vaccinated people can remove their hats without trouble by tugging upward, say doctors [Box 4] Physicists say Dorito powder is affected by gravity [Box 5] Steering wheels will work normally on Dec 12th; make left and right turns as usual [Box 6] CNN investigation: Santa's skin is dry and healthy this year, with the same amount of oil as before [Caption below the panel:] I don't know whether the "Don't repeat the claim in the headline debunking it" thing works or not, but it definitely makes reading the news weird.

The Last Molecule

The Last Molecule

https://www.xkcd.com/2552

https://www.explainxkcd.com/wiki/index.php/2552:_The_Last_Molecule

[Ponytail is presenting on a stage. To the top-center of the slide which Ponytail is pointing to, there is a circled "100% complete" under "Chemistry", then to the left is "Biology" which is at "93% complete" and to the right is "Physics" which is at "98% complete". The bottom of the slide shows the structural formula of a molecule which is captioned "The Last One", along with a few smaller captions around it drawn as squiggles.] Ponytail: With the discovery of the last molecule, I'm pleased to announce that chemistry is finally complete. Ponytail: Best of luck to our competitors in their race for second place.

This comic jokingly proposes a situation in which chemists have discovered and catalogued every single possible molecule. Thus they declare they have "completed chemistry." As deep learning algorithms can now predict chemical properties of proteins in advance of measurement, this situation may be looming closer. Like comic 2268 , this may be a reference to a quote from around 1900, often attributed to Lord Kelvin or Albert Michelson: "There is nothing new to be discovered in physics now. All that remains is more and more precise measurement." More likely, this is a reference to attempts by Frege and by Russell and Whitehead a century ago to prove using symbolic logic the completeness of arithmetic. This turned out to be impossible since Kurt Goedel's famous Incompleteness Theorem proved that at least one proposition could neither be proved true or false. Against this background, the idea that natural sciences could be 90+% complete is humorously exaggerated. In real life the number of ways to arrange atoms into molecules grows combinatorically with the number of atoms in a molecule. Since molecules can be extremely large (up until the point where gravity takes over and initiates nuclear fusion), the number of possible combinations is much much larger than the number of particles in the observable universe, making the full cataloging of all molecules impossible. Thus, a "final molecule" cannot be reached. In addition, chemistry is the study of the interaction and changing states of atoms and molecules, not simply the cataloging of all specimens of molecule. Even if we did have a list of every molecule, there are a far greater number of ways to continue studying them, so the field would still be nowhere near completed. This is reminiscent of biology's focus in previous centuries on simply cataloging the species on Earth, or Mathematics' classification of finite simple groups (only the latter was, surprisingly, actually completed successfully). Further, the goal of science is not to "complete" a field, but to understand it better and better (finite order group theory did not shutter its doors after all finite simple groups were classified). No scientific field is considered fully understood (or rather, it is then considered a specialisation of a wider field). As readers are aware of this, part of the humor comes from the very high percentages given to the different fields. Putting Biology at 93% and Physics at 98% is patently absurd. Another part of the humor is the precision. As mentioned in the title text, we can't even give a definitive answer to changing-target yet deceptively simple questions like "How many kinds of ants are there?" If biology were simply a matter of cataloging species, we are currently at around 10-20%. And yes many of them are ants; when J.B.S Haldane, founder of the field of population genetics, was asked what he learned about God from studying creation, he reportedly said "God is incredibly fond of beetles" . Counting species aside, fundamental and important problems such as what genes promote which traits, the nature of cognition, and the mechanism behind several diseases remain complete mysteries. We know less about our own ocean floor than we do about the surface of Mars. As for Physics, all the elementary particles of the Standard Model of particle physics have been experimentally detected, culminating in the 2012 detection of the Higgs Boson . But questions such as "what is dark matter?", "how do we unify the four fundamental forces?", "how do we make nuclear fusion possible on earth?", "is the speed of light symmetrical?", and "how many dimensions does the universe have?" make it clear that the field still has a long, long way to go. The title text in particular makes fun of Biology lagging behind due to the inherent difficulty of cataloging all species. Species are being constantly created and recategorized, so even if it were possible to know exactly what animals were alive on Earth at any one time, and which could interbreed, there would still be no agreement on the number of species they constituted, and that's without even getting into historic species, such as the contentious question of whether Neanderthals are considered a subspecies of homo sapiens, or a whole separate species. [Ponytail is presenting on a stage. To the top-center of the slide which Ponytail is pointing to, there is a circled "100% complete" under "Chemistry", then to the left is "Biology" which is at "93% complete" and to the right is "Physics" which is at "98% complete". The bottom of the slide shows the structural formula of a molecule which is captioned "The Last One", along with a few smaller captions around it drawn as squiggles.] Ponytail: With the discovery of the last molecule, I'm pleased to announce that chemistry is finally complete. Ponytail: Best of luck to our competitors in their race for second place.

Incident Report

Incident Report

https://www.xkcd.com/2553

https://www.explainxkcd.com/wiki/index.php/2553:_Incident_Report

Facility: East Valley Nuclear Plant Date: 12/10/2021 Report ID: 9603120071 Event description: Roughly 18 hours prior to the incident, an Amazon package containing fireworks was mistakenly delivered to the reactor control room and left under the console. The next day, at approximately 14:00 , Technician A arrived at the facility with a bag containing four juggling pins. At 14:20 , Technician A entered the control room, and joined Technician B at the console. At 14:28 , Technician C exited the elevator and approached the control room holding a birthday cake intended for Technician B. At 14:29:22 , Technician A said "Hey [Technician B], check out this cool trick I learned" while taking out the juggling pins. Technician B turned to look just as, at 14:29:26 , Technician C entered holding the cake. [Caption below the panel]: You know things are about to get bad when the incident report starts including seconds in the timestamps.

An incident report describes the sequence of events when something goes wrong, including the lead-up as well as the aftermath. This usually involves describing at what time related events happen. In this comic, a report at a nuclear power plant on the day of the comic's publishing starts with particularly vague timestamps (that a package of fireworks arrived "roughly 18 hours prior" to it), then uses approximate minute-level precision ("14:00" and "14:20", which could reasonably be five minutes off in either direction), then minute-level precision ("14:28"), then second-level precision ("14:29:22" and "14:29:26"). This suggests that the clock time is really a proxy for the amount of time before one specific moment where everything falls apart, and when seconds start appearing, it implies that the recollection is within a few minutes of the disaster. Normally the increased level of precision reflects close monitoring capabilities of the affected systems, reviewing monitoring equipment, such as surveillance camera and microphone recordings, and/or detailed analysis by incident investigators. It may have been sufficient for the resulting inquiry to merely note the prior arrival of the original package, and possibly then read off (whatever remains of) the signing-in logs for the approximate times each member of staff arrives on the scene. At some point, though, the investigation will refer to fully timestamped security recordings, perhaps even eventually frame-by-frame with particular interest in exactly which things touched exactly what other things, in sequence, in order to hopefully learn all the necessary lessons about the incident. Synchronization of events is important in incident investigations , so often systems are required to take input from common, relatively precise time references, such as GPS , WWV broadcast , or cellular telephone systems. For example, an aircraft crash needs radar positioning data synced with voice communications and flight recorder data . Lack of correlation between these is a potential source of conspiracy theories, for example one of the hijacked planes on 9/11 crashed into Pennsylvania either at 10:03 or 10:06 depending on two different information sources. In many situations, incident reports are anonymized as shown to protect the identities of those people involved in the incidents. This is often done to prevent unnecessary blaming of certain individuals, particularly when it hasn't yet been determined whether the incident was negligence or just an accident. Examples of real-life incident reports with second-level precision timestamps showing the increasing precision around critical moments include: The report shown cuts off before reaching the actual incident, leaving it to the reader to imagine what happened next. If the birthday cake has lit candles, one possible sequence of events is that a dropped or badly thrown juggling pin could have hit one of them and then rolled over to the fireworks package, thus igniting the package. This would have caused the fireworks to go off underneath the reactor control's console. Although the comic refers to juggling "pins" , jugglers commonly call those props "clubs." It is possible Randall is confusing the similarly shaped objects in 10-pin bowling to juggling clubs. "Pins" are another name for a component of Uranium Carbide type nuclear fuel rods , which are involved in the safe control of the nuclear reaction within a nuclear power plant. No sane reactor staff would juggle these complex, heavy and expensive pieces of equipment. [ citation needed ] The title text refers to the theme music from the 1975 film Jaws , which has come to represent impending danger. Movies use music to create the correct emotional tone; suspenseful music indicates that something bad is about to happen. The Jaws theme is an iconic example, famously used to create a sense of foreboding, then uses increasingly rapid tempo to build a sense of imminent danger, culminating in a dramatic moment of disaster (a shark attack, in the film). As with the increasing tempo of this theme, the increasing precision with which events are recorded in an incident report build the increasing sense that something terrible is imminent. 9603120071 is an actual accession number for an incident at San Onofre Nuclear Generating Station in 1996. Four slightly contaminated stray kittens were found, cleaned, and adopted. No clock times were mentioned in the report. Real-world nuclear power stations have strictly regulated control rooms which would prevent the simultaneous presence of fireworks, juggling and birthday celebrations. [1] [2] There is no East Valley nuclear power plant, but there are two reactor units at the nuclear power plant in Beaver Valley, Pennsylvania. Facility: East Valley Nuclear Plant Date: 12/10/2021 Report ID: 9603120071 Event description: Roughly 18 hours prior to the incident, an Amazon package containing fireworks was mistakenly delivered to the reactor control room and left under the console. The next day, at approximately 14:00 , Technician A arrived at the facility with a bag containing four juggling pins. At 14:20 , Technician A entered the control room, and joined Technician B at the console. At 14:28 , Technician C exited the elevator and approached the control room holding a birthday cake intended for Technician B. At 14:29:22 , Technician A said "Hey [Technician B], check out this cool trick I learned" while taking out the juggling pins. Technician B turned to look just as, at 14:29:26 , Technician C entered holding the cake. [Caption below the panel]: You know things are about to get bad when the incident report starts including seconds in the timestamps.

Gift Exchange

Gift Exchange

https://www.xkcd.com/2554

https://www.explainxkcd.com/wiki/index.php/2554:_Gift_Exchange

[Ponytail is talking to Cueball.] Ponytail: Ugh, I have to organize a fair gift exchange for my survey-loving family. Ponytail: Do you want to help? Ponytail: They said it's "okay if it's complicated." [Caption below the panel:] The perfect gift for a political scientist

In December, white elephant gift exchange parties are popular, in which party-goers bring and exchange presents, via a variety of procedures which often involve individuals taking turns to pick a present. Usually they can either pick a wrapped present and open it, or take a present that someone else has opened already. Many political scientists think that creating a fair gift exchange is a really tricky problem, since it involves different valuation of various goods (one person might like socks while another person would not), a possible incentive to misrepresent how much you value things ("You're going to have to offer me a LOT to give up these socks, because I really like them"), arbitrary order effects (who goes first matters), and more. These problems have a lot of political analogues in the political science topics of social choice theory and mechanism design , and many political scientists dedicate years of their life to figuring out the best solutions. Therefore, a political scientist would enjoy the challenge of creating a fair gift exchange; it is the best gift that Ponytail could have given them. The scenario Ponytail presents is formally known as a fair item allocation problem, for which there are various approaches to how to define fair , and various proposed allocation algorithms, some of which are computationally intractable even for small numbers of participants. The fact that the family loves surveys implies that a favourite method of political scientists, surveying the electorate, would be greatly appreciated. The "It's okay if it's complicated" line is funny because many of the theoretically best solutions a political scientist might come up with would be very complicated--far more so than the typical person would want to think about. In the title text, having well-formatted budgets makes a scientist's job much easier since it is better for data manipulation. In the same way, expressing preferences on a well-calibrated numerical scale makes data manipulation simple and straightforward. Therefore, Ponytail's scenario is an excellent gift for the political scientist. It also extends the humorous scenario of the nerdy family who enjoy filling in complex surveys - the same family would be likely to enjoy a well-formatted budget spreadsheet. [Ponytail is talking to Cueball.] Ponytail: Ugh, I have to organize a fair gift exchange for my survey-loving family. Ponytail: Do you want to help? Ponytail: They said it's "okay if it's complicated." [Caption below the panel:] The perfect gift for a political scientist

Notifications

Notifications

https://www.xkcd.com/2555

https://www.explainxkcd.com/wiki/index.php/2555:_Notifications

[White Hat, Megan and Cueball are standing next to each other. White Hat is separated from the other two figures by a small margin.] White Hat: And another thing that annoys me about people is... Cueball: This user has notifications turned off. [The camera zooms in on Megan and Cueball. Megan turns to look at Cueball.] Cueball: They will see your messages when they're back. Cueball: Notify anyway? [The camera zooms outward to show White Hat. Megan turns back to look at White Hat. All three figures are standing silently.] [Megan turns to look at Cueball again.] Megan: What are you-- Cueball: Shhh- It's working.

Many devices will notify the user when something of possible interest occurs (e.g., a new phone call is received, a load of laundry is done). Some, such as the instant messaging software Slack , allows you to turn notifications off while you're offline or away (or just don't want to be disturbed). Such a function would be desirable in real life, as illustrated here. The sender can sometimes override this and notify the user anyway. White Hat is telling Cueball and Megan about "another thing that annoys [him] about people," which means that either the strip begins after he has already vented a long series of gripes, or he is prone to spontaneously airing one of his many grievances non sequitur . (Both of those traits could be something that annoys Cueball about people.) Cueball responds by "turning off his notifications" from White Hat. White Hat immediately falls silent, sparing Megan and Cueball from further boring "conversation". Maybe Cueball has picked up the "Commented" trick , White Hat is thrown off by the unusual statement, or it could be that he just naively takes Cueball at his word. Either way, now that he "knows" that he will not receive any further immediate engagement from Cueball, he thus gives up, for the time being, talking at Megan and Cueball about his annoyance(s). If he believes the premise, he might recite the rest of his conversation as soon as Cueball supposedly turns notifications back on. His behavior is reminiscent of a user who is logged into a chat server but is "away from keyboard" and totally disengaged. Megan starts to ask Cueball what he's doing, but Cueball shushes her to let it 'keep working' -- presumably, if Megan speaks up, she might alert White Hat that Cueball is still listening and draw him back into conversation. In the title text, this is taken even further by combining this with a standard real-life reason (or excuse) to leave a social situation: that the person has to leave because it is getting late. It is often used when someone really has a thing early the next day and wants to get home early to get enough sleep to be prepared for the "thing", but the vagueness of the thing suggests that they just want to get out of uncomfortable company or situations. The specific time, 10:34 pm, informs the messenger (who could be anywhere) of the user's time zone, and tells the one that wishes to notify that it is past the normal bedtime in the user's time zone. And this is why the program would normally ask if they still really wish to notify them, since they would risk waking the recipient up. This could cause annoyance if the message is not urgent and important. In this case, however, it is clear he is awake and wants to leave the social situation, supposedly because of a thing he has the next day. In this situation, it is funny because apparently it's Cueball talking about himself in the third person to another person who knows they are in the same time zone, and unless all of the characters are out really late it's unlikely that it's actually that late at night in "Cueball's time zone" at the moment. An alternate explanation is that the comic highlights how strange it is that the "This user has notifications off, Notify anyway?" pop-up can sometimes leave one paralyzed with indecision, despite the fact that it does literally nothing to stop you from sending the text as normal. If it pops up when you send a text, now you have to decide whether your text is important enough to notify the person you have texted, even though they have notifications off. It's the same situation as if you're told that your boss is doing something important. You could be paralyzed, trying to figure out whether "the machine ran out of batteries" is more important than whatever generic "important thing" the other person is doing. Plus, now you have to factor in things like whether your interruption will cause more harm than help, how long it'll take, etc. If Cueball just "Blocked" notifications from white hat, White Hat would simply be annoyed and just keep talking (because blocking implies that you just don't want to talk anymore.) However, by giving White Hat the option to "Notify anyway", Cueball paralyzes White Hat with indecision, as shown by him not doing anything for multiple panels. This is ironic, as when users are given the option to "Notify anyway", it basically renders the action of turning off notifications useless because anyone can bypass the system. However, it still works to stop most message notifications, because no one wants to bypass the filter and risk annoying the person who turned off notifications. This may be why Cueball shushes Megan to let it 'keep working'; If Megan speaks up, White Hat might realize that Cueball's 'filter' does literally nothing to stop his messages, and White Hat would resume his rant. [White Hat, Megan and Cueball are standing next to each other. White Hat is separated from the other two figures by a small margin.] White Hat: And another thing that annoys me about people is... Cueball: This user has notifications turned off. [The camera zooms in on Megan and Cueball. Megan turns to look at Cueball.] Cueball: They will see your messages when they're back. Cueball: Notify anyway? [The camera zooms outward to show White Hat. Megan turns back to look at White Hat. All three figures are standing silently.] [Megan turns to look at Cueball again.] Megan: What are you-- Cueball: Shhh- It's working.

Turing Complete

Turing Complete

https://www.xkcd.com/2556

https://www.explainxkcd.com/wiki/index.php/2556:_Turing_Complete

[Ponytail has raised her hand, palm up, as she addresses Cueball.] Ponytail: ...Now, it turns out this is actually Turing-Complete... [Caption below the panel:] This phrase either means someone spent six months getting their dishwasher to play Mario or you're under attack by a nation-state.

A Turing machine is a theoretical computer that has an infinite tape of symbols. It can read and change the symbols on the tape as it moves up and down this tape according to a set of instructions (program). This very simple machine can be shown to do every computational task that what we think of as a "computer" can do, given the right program and enough time. Something that is Turing complete is able to act as a Turing machine, though generally physical examples are limited to having a finite tape, [ citation needed ] and this means it is also able to do basically every computational task. Many pieces of hardware and software are supposed to be Turing complete (even Excel, as previously pointed out in 2453: Excel Lambda ). Some other things turn out to be Turing complete, even if they weren't designed for it (for instance, the tabletop game Magic: The Gathering or, at least within xkcd meta-reality, rocks in a desert ). Whatever Ponytail has been referring to is not shown, but it seems to be an anecdote about how something seemingly too simple and/or specialised to exhibit such a computational equivalence has been discovered to actually be that capable. Ponytail may refer to the recent articles about the background of the NSO zero click exploit for iPhones, e.g. this . Mario is the lead character in a long running series of video games including Donkey Kong , Super Mario Bros and Mario Kart . Running video games, such as Doom , is one common way of demonstrating the ability to run arbitrary programs on devices that were not intended as general purpose computers. With complex processors being installed in more and more devices, it's plausible that someone could get a dishwasher to play Mario. However, another reason to make a device run arbitrary code is to breach security. If the owner of a system assumes that it can only do one specific thing, like operate a dishwasher, they may not take precautions against hacking. But if the system is actually Turing-complete, a hacker could potentially make it do something else, like become part of a botnet . Therefore, "this is actually Turing-complete" could be the prelude to a complicated hacking attempt. Sophisticated hacking attacks are often the work of hackers that have the support of a government, or nation-state . The ForcedEntry exploit is a way that was developed to allow PDF files to force malware onto various devices. PDF files are normally used to present documents. The exploit uses a PDF's ability to do logic operations on pixels to implement a simple virtual CPU within one of the PDF renderer's decompression functions. Constructing a CPU in this way is similar to how a hardware CPU is made of individual logic gates. ForcedEntry was publicized a few days before this comic came out. In the title-text it is suggested that this mechanism can be used for what might be more legal and practical purposes, although this might be up to some interpretation depending upon who has the right (and permission) to do what. A tech stack is one shorthand way of describing the way an integrated grouping of communicating software packages provides everything from the deepest data handling (even as low-level as an operating system itself) to the user interface. All of these will normally be on a computer (or possibly many of them, whether locally or distributed worldwide) and if a sufficiently functional surrogate system is capable of emulating this (computing what the original computer(s) would do) then it can be considered to effectively be the same stack of technology and duplicate or replace the originals. [Ponytail has raised her hand, palm up, as she addresses Cueball.] Ponytail: ...Now, it turns out this is actually Turing-Complete... [Caption below the panel:] This phrase either means someone spent six months getting their dishwasher to play Mario or you're under attack by a nation-state.

Immunity

Immunity

https://www.xkcd.com/2557

https://www.explainxkcd.com/wiki/index.php/2557:_Immunity

[White Hat has raised his hand, palm up, as he addresses Cueball.] White Hat: See, it's good to get infected, because it gives you immunity. [White Hat has lowered his arm.] Cueball: Why would I want immunity? [Same setting.] White Hat: To protect you from getting inf... White Hat: ...wait.

This comic is, although not specifically referenced, another entry in a series of comics related to the COVID-19 pandemic . A common issue posited by people opposed to vaccination , especially during the COVID-19 pandemic, is that there are other ways to become immune to diseases caused by viruses or bacteria — most notably, contracting the disease "naturally". Cueball , by way of questioning, points out to White Hat that this makes no sense. Contracting the natural disease is the thing people are trying to prevent . Diseases are bad. [ citation needed ] Although there are plenty of instances where someone has already recovered, and therefore is in possession of natural immunity , it would be better to have that immunity without getting sick at all. Especially with a disease like COVID that can cause permanent damage even to those who eventually clear the virus. Vaccination provides similar immunity without the negative effects of infection. While explaining that getting infected is the best way to avoid getting infected, White Hat thus realizes the circular logic presented by anti-vaxxers , and thus stops mid sentence. The title text elaborates on this by pointing out that people with no understanding of the immune system will understand that contracting a disease to avoid contracting a disease is a bad idea, and that people with a strong understanding of the immune system will understand the specific ways it can fail (and that vaccines provide a greater benefit for less risk). It is thus only people with a limited understanding of the immune system, who know that infection can provide immunity but haven't thought out the disadvantages of catching the disease, who would make a claim such as White Hat does. The comic does not specifically reference vaccines and anti-vaxxers. It could also be about people who refuse to wear masks and social distance during the pandemic, who do not understand how much they are putting other people at risk. White Hat may even be fumbling an explanation of his previous 2515: Vaccine Research into why vaccines are good. Older folks may be familiar with the "infection gives you immunity" trope due to their experience with so-called "childhood diseases". Before there were vaccines for e.g. measles , mumps , and chickenpox , it was seen as preferable for young children to contract these diseases, because the risk of serious illness is greater for those who get "first infections" later in life. Children run a comparatively smaller risk of serious illness in return for (usually) life-long immunity. Note that this only ever made sense for children whose immune system is still flexible enough to adapt, and not for 30 something fitness bros. Furthermore, the trope has outlived its context. Small as the risk to children of serious illness from measles, mumps, and chickenpox might be, vaccines all but eliminate the risk of contracting serious symptoms at all, so there is no sensible reason to subject oneself to infection. The trope, moreover, is misapplied to COVID-19, because, on present evidence, immunity from infection is short-lived (which, at least at the time of this comic, was exacerbated by the fact that variants with sufficiently different spike proteins to at least partially evade natural immunity (such as beta, delta, and omicron) were arising at a rate of multiple per year), so there is no benefit to be gained by running the risk of winding up in the hospital - or the morgue. The better comparison is to influenza , which people get vaccinated against every year. Instead of childhood diseases, think of diseases that had a high probability of serious illness at any age, such as poliomyelitis and smallpox , for which few accepted the "infection gives you immunity" trope (even though, for those diseases, infection typically yielded life-long immunity), and there was far less resistance to effective vaccines once these became available. [White Hat has raised his hand, palm up, as he addresses Cueball.] White Hat: See, it's good to get infected, because it gives you immunity. [White Hat has lowered his arm.] Cueball: Why would I want immunity? [Same setting.] White Hat: To protect you from getting inf... White Hat: ...wait.

Rapid Test Results

Rapid Test Results

https://www.xkcd.com/2558

https://www.explainxkcd.com/wiki/index.php/2558:_Rapid_Test_Results

[Header above the comic:] Interpreting Rapid Test Results [What follows is a set of 8 possible rapid test results for COVID-19.] [One line on the "C".] Negative [Two lines, one on the "C" and one on the "T".] Positive [Two curvy lines on the "C" and the "T", resembling the "approximately equal" sign.] Approximately positive [Two lines, not on the "C" or the "T", but they are instead closer together.] Positive (college ruled) [Five lines resembling a cell signal symbol.] Good cell signal [Two straight lines, on the "C" and "T", with lines going outward from the centre, giving an illusion of the lines being curved.] Did you know these lines are actually parallel? [One line on the "C", and two lines in a cross with one line sticking upward of the center of the cross.] The Blair Witch is near [Three lines, with one on the "C", one on the "T", and one in the middle of the "C" and "T".] Click to expand Covid menu

This comic is another in a series of comics related to the COVID-19 pandemic . This comic is a joke about COVID-19 rapid lateral flow test results. These devices are used in many countries for individuals to test their own nasal and oropharynx fluid for evidence of COVID-19 virus to detect asymptomatic infection. These tests have two indicator strips - a test line for covid-19 and a control line to check the device is working correctly. Where a control line is not present, the test should be ignored and repeated. Until comparatively recently pregnancy was the occasion most familiar for requiring this form of test) The first 2 answers are the standard indicators for a negative and positive result, but Randall takes this to absurdity, see below in the table . The title text interprets the hyphen in "Covid-19" as a negative sign to make a mathematical joke (or possibly a reference to antimatter , which in reality mutually annihilates when coming into contact with regular matter). Here Randall postulates a counterpart virus to Covid-19, resulting in a test with inverted colors, which he names Covid+19. When combined this anti-coronavirus exactly matches the original one and results in zero Covid, curing those who had previously been infected. This was the last comic before this year's Christmas comic . It was about Covid-19 testing. The last comic before the 2020 Christmas comic, 2402: Into My Veins , was about the Covid-19 vaccine. [Header above the comic:] Interpreting Rapid Test Results [What follows is a set of 8 possible rapid test results for COVID-19.] [One line on the "C".] Negative [Two lines, one on the "C" and one on the "T".] Positive [Two curvy lines on the "C" and the "T", resembling the "approximately equal" sign.] Approximately positive [Two lines, not on the "C" or the "T", but they are instead closer together.] Positive (college ruled) [Five lines resembling a cell signal symbol.] Good cell signal [Two straight lines, on the "C" and "T", with lines going outward from the centre, giving an illusion of the lines being curved.] Did you know these lines are actually parallel? [One line on the "C", and two lines in a cross with one line sticking upward of the center of the cross.] The Blair Witch is near [Three lines, with one on the "C", one on the "T", and one in the middle of the "C" and "T".] Click to expand Covid menu

December 25th Launch

December 25th Launch

https://www.xkcd.com/2559

https://www.explainxkcd.com/wiki/index.php/2559:_December_25th_Launch

[Close-up of the top of the James Webb Space Telescope launch rocket. A "Webb" logo can be seen alongside other indistinct logos. Some clouds and birds are visible in the background.] Caption: T-minus 10...9...8... [Zoom-out to show the complete rocket and the ground below. The rocket takes up the bottom-left corner. At the top-right, Santa Claus and a line of reindeer are flying in towards the left.] Santa: Ho ho ho! Santa: Merry Christmas! [Ponytail and Cueball sitting at mission control consoles.] Cueball: Oh no.

The James Webb Space Telescope (JWST) is a space telescope jointly developed by NASA, the European Space Agency, and the Canadian Space Agency. It has suffered many, many delays over its development period (as previously referenced in 2014: JWST Delays ), but it finally launched on Christmas day, December 25, 2021. This was about 7 hours after this comic appeared. The release day of this comic was Christmas Eve the 24th of December. As can be seen from when this page was created 05:02:00, 25 December 2021 (UTC), the comic came out at least 7 hours before launch which was 12:20:00, 25 December 2021 (UTC). Since Boston ( Randall's home town) is 5 hours after UTC then the comic must have released close to midnight on the 24th for Randall, and clearly before midnight for the rest of the time zones in the US. Web comics are usually drawn some time in advance. When this comic was drawn and scheduled for publication, it is possible NASA had not yet announced that the launch of JWST was slipping from Christmas Eve to Christmas Day. The launch was probably three days after Randall opened the last number in his Webb advent calendar. (Thus this is the second Christmas comic this year referring to the telescope). In this comic, the James Webb Space Telescope is finally ready to take off. However, an unfortunate circumstance occurs: Santa Claus himself, presumably on his way to or from delivering presents to children, crosses into the path of the launch rocket. The joke is the implication that, right on the brink of success, this extraordinarily unlucky incident will either destroy the telescope, harm Santa, or cause yet another delay, much to Cueball 's horror. Real launch aborts have occurred with fewer than 2 seconds left in the countdown, causing delays of over a month. According to the title text, the range safety officer has made the decision to shoot down Santa Claus's sleigh, in order to clear the sky above, protecting the launch window. This seems to demonstrate that they are determined not to let anything delay the launch any further (or that given a choice between destroying the telescope or destroying Santa, the range safety officer chooses the latter). "Range Safety Officer" is the job title of a person in charge of the safety of a launch. Airspace is normally closed to air traffic to avoid collisions between aircraft and rocket launches. While Santa might not know about such restrictions, he already knows about this particular launch because thousands of astronomy geeks have asked for a new space telescope as a Christmas present in their letters to Santa, and the easiest way for Santa to deliver such a present is just keeping a safe distance from the launch pad. Moreover NORAD tracks Santa 's flying around the world and would be able to give sufficient warning to both Santa and Ground Control to prevent such a close encounter of a festive kind; as well as to prevent accidental global thermonuclear war by confusing a pack of flying reindeer with a first-strike attack by a foreign power. Finally, Santa Claus performs deliveries overnight, while the launch is scheduled for morning local time , so the timing of such a collision would not occur. The JWST has been referenced previously in 1730: Starshade , 2014: JWST Delays , 2447: Hammer Incident and 2550: Webb , is on the list of payloads in 1461: Payloads and its planned use was indirectly referenced in 975: Occulting Telescope . Santa is known to maintain a list of humans responsible for technological incidents and to have suitable punishment for offenders. 12 days after launch it was referenced again in 2564: Sunshield . [Close-up of the top of the James Webb Space Telescope launch rocket. A "Webb" logo can be seen alongside other indistinct logos. Some clouds and birds are visible in the background.] Caption: T-minus 10...9...8... [Zoom-out to show the complete rocket and the ground below. The rocket takes up the bottom-left corner. At the top-right, Santa Claus and a line of reindeer are flying in towards the left.] Santa: Ho ho ho! Santa: Merry Christmas! [Ponytail and Cueball sitting at mission control consoles.] Cueball: Oh no.

Confounding Variables

Confounding Variables

https://www.xkcd.com/2560

https://www.explainxkcd.com/wiki/index.php/2560:_Confounding_Variables

[Miss Lenhart is holding a pointer and pointing at a board with the a large heading with some unreadable text beneath it. Below this there are two graphs with scattered points. In the top graph the points are almost on a straight increasing line. In the bottom the data points seem to be more random. Mrs Lenhart covers most of the right side of the board, but there is more unreadable text to the right of her.] Miss Lenhart: If you don't control for confounding variables, they'll mask the real effect and mislead you. Heading: Statistics [Miss Lenhart is holding the pointer down in one hand while she holds a finger in the air with the other hand. The board is no longer shown.] Miss Lenhart: But if you control for too many variables, your choices will shape the data and you'll mislead yourself. [Miss Lenhart is holding both arms down, still with the pointer in her hand.] Miss Lenhart: Somewhere in the middle is the sweet spot where you do both, making you doubly wrong. Miss Lenhart: Stats are a farce and truth is unknowable. See you next week!

In statistics, a confounding variable is a third variable that's related to the independent variable, and also causally related to the dependent variable. An example is that you see a correlation between sunburn rates and ice cream consumption; the confounding variable is temperature: high temperatures cause people go out in the sun and get burned more, and also eat more ice cream. One way to control for a confounding variable by restricting your data-set to samples with the same value of the confounding variable. But if you do this too much, your choice of that "same value" can produce results that don't generalize. Common examples of this in medical testing are using subjects of the same sex or race -- the results may only be valid for that sex/race, not for all subjects. There can also often be multiple confounding variables. It may be difficult to control for all of them without narrowing down your data-set so much that it's not useful. So you have to choose which variables to control for, and this choice biases your results. In the final panel, Miss Lenhart suggests a sweet spot in the middle, where both confounding variables and your control impact the end result, thus making you "doubly wrong". "Doubly wrong" result would simultaneously display wrong correlations (not enough of controlled variables) and be too narrow to be useful (too many controlled variables), thus the 'worst of both worlds'. Finally she admits that no matter what you do the results will be misleading, so statistics are useless. This would seem to be an unexpected declaration from someone supposedly trying to actually teach statistics [ citation needed ] , and expecting her students to continue the course. Though there is a possibility that she is not there to purely educate this subject, but is instead running a course with a different purpose and it just happens that this week concluded with this particular targeted critique. In the title text, the residual refers to the difference between any particular data point and the graph that's supposed to describe the overall relationship. The collection of all residuals is used to determine how well the line fits the data. If you control for this by including a variable that perfectly matches the discrepancies between the predicted and actual outcomes, you would have a perfectly-fitting model: however, it is nigh impossible (especially in the social and behavioral sciences) to find a "final variable" that perfectly provides all the "missing pieces" of the prediction model. [Miss Lenhart is holding a pointer and pointing at a board with the a large heading with some unreadable text beneath it. Below this there are two graphs with scattered points. In the top graph the points are almost on a straight increasing line. In the bottom the data points seem to be more random. Mrs Lenhart covers most of the right side of the board, but there is more unreadable text to the right of her.] Miss Lenhart: If you don't control for confounding variables, they'll mask the real effect and mislead you. Heading: Statistics [Miss Lenhart is holding the pointer down in one hand while she holds a finger in the air with the other hand. The board is no longer shown.] Miss Lenhart: But if you control for too many variables, your choices will shape the data and you'll mislead yourself. [Miss Lenhart is holding both arms down, still with the pointer in her hand.] Miss Lenhart: Somewhere in the middle is the sweet spot where you do both, making you doubly wrong. Miss Lenhart: Stats are a farce and truth is unknowable. See you next week!

Moonfall

Moonfall

https://www.xkcd.com/2561

https://www.explainxkcd.com/wiki/index.php/2561:_Moonfall

[Cueball and Megan walking to the right] Megan: Are you excited for Moonfall ? Megan: Or cringing? Cueball: Well... [Closeup on Cueball] Cueball: I like when stories are grounded in good science because it's exciting to expand our ideas of what's possible. [Zoomed back out to Cueball and Megan walking to the right. Cueball has his palms raised] Cueball: But I also support giving Roland Emmerich as much money as he wants to make cool spaceship noises and smash moons into things. Megan: Excited to expand our ideas of how much stuff can explode at once.

Megan asks Cueball if he is excited for the release of the movie Moonfall . Moonfall was released in February 2022, a couple of months after this comic. Its director, Roland Emmerich , is known for blowing up things in his movies (see for instance the Roland Emmerich Supercut ), as well as for factual inaccuracies in his work (mainly the scientific implausibility of his many disaster movies like Independence Day , The Day After Tomorrow and 2012 ). The plot of Moonfall is scientifically preposterous, making it potentially "cringe-worthy" for someone who enjoys "hard" science fiction, like Cueball. For the moon to fall from the sky, it would have to stop orbiting. Most forces applied it to will simply change the way in which it is orbiting, making the orbit more elliptical, larger or smaller. To stop it from orbiting entirely, a 'braking' force would need to be applied in the opposite direction of its travel, to halt it. The moon's mass is about 7.34767×10 22 kg and its speed about 1.022 km/s, so the energy needed to stop it is ½ mv 2 or about 3.8364×10 28 joules. That's about the energy of 1 trillion large nuclear explosions, centered on the leading-most point of the moon's surface. A precisely-oriented stellar body could strike the moon to do this, like a billiard ball colliding with tons of interstellar moon shrapnel instead of dust. Less counteractive energy could make the Moon change orbit to one with a perigee below the surface of the Earth, close enough to (partially) enter the atmosphere or merely bring it down beneath the applicable Roche limit . These scenarios would be only technically less catastrophic, and whether the Moon fragments from the initially applied force, the stresses of its nearest (non-contact) distance to Earth or actually survives largely intact until there is a more direct physical interaction, the precise degree of the effect might be practically academic. Cueball explains to Megan that he usually likes it when stories are based on good science. Maybe only bending it a bit to create the story, to expand our ideas of what is possible. But then he goes on to state that he supports giving Roland Emmerich as much money as he wants, to make cool spaceship noises and smash moons into things. In the movie it is only a moon (the Moon , presumably, see the plot below). But in general Roland often uses huge explosions in his movies, something also previously said about other similarly-styled directors like Michael Bay . Megan sums the situation for Cueball up, stating that he is excited to expand our ideas of how much stuff can explode at once. In the title text Cueball continues by explaining that while novel ideas and explosions are good, what he really want from a movie is novel ideas about cool explosions. So new ways to explode things, or ideas about exploding more things at once. Or both. In 1536: The Martian a similar discussion of an upcoming movie is made for The Martian . But in that case it is the scientific accuracy that is the subject, and the lack of huge explosion that makes it hard to believe it could become a big budget movie! It is very rare that Randall makes a movie review like in those two comics. Spoiler Alert In Moonfall, a mysterious force knocks the Moon from its orbit around Earth and sends it hurtling on a collision course with life as we know it. With mere weeks before impact and the world on the brink of annihilation, NASA executive and former astronaut Jo Fowler is convinced she has the key to saving us all - but only one astronaut from her past, Brian Harper[,] and a conspiracy theorist K.C. Houseman believe her. These unlikely heroes will mount an impossible last-ditch mission into space, leaving behind everyone they love, only to find out that our Moon is not what we think it is. —Centropolis Entertainment, quoted at IMDB [Cueball and Megan walking to the right] Megan: Are you excited for Moonfall ? Megan: Or cringing? Cueball: Well... [Closeup on Cueball] Cueball: I like when stories are grounded in good science because it's exciting to expand our ideas of what's possible. [Zoomed back out to Cueball and Megan walking to the right. Cueball has his palms raised] Cueball: But I also support giving Roland Emmerich as much money as he wants to make cool spaceship noises and smash moons into things. Megan: Excited to expand our ideas of how much stuff can explode at once.

Formatting Meeting

Formatting Meeting

https://www.xkcd.com/2562

https://www.explainxkcd.com/wiki/index.php/2562:_Formatting_Meeting

[A screen is shown which displays five rows of text, the top three above a dividing line. To the right of the screen the upper part of Cueball is visible as he delivers a message concerning the text on the screen:] Localization working group Upcoming meetings ----------------- US Team: 2/3/22 EU Team: 2/3/22 Cueball: And the European formatting and localization team will meet a month later...

In the United States , it's common to write dates numerically in the format month / day / year -- 2/3/22 means February 3, 2022 (the century is often omitted when it's obvious that the date is around the current time). In Europe, the usual order is day/month/year - so 2/3/22 is 2nd March, 2022. " Localization " is the technique used in software to make it accept input and display output in the formats most natural to users in their locations. For example, in the United States numbers use commas "," to separate thousands and a decimal point "." to separate the decimal values, while in large areas of the EU it is the reverse . And the textual output will be translated to the local language. Naturally, this also includes displaying dates in the local format, as described above. Localization may also include the adoption of the tax law to the location, for instance when adopting tax software made for the US to the UK. The joke in this comic is that two dates are shown, on the same display , relating to meetings regarding localization. The date of the meeting of the US team is localized in the US format while the EU team's meeting is localized in the European format, and these two dates (about a month apart) happen to be formatted the same (there are 64 such pairings of dates, as long as the day of the month of one is between 1 and 12 and not equal to the presumed month of the other). Cueball needs to explain that the European meeting will be a month later than the US meeting to avoid any confusion due to the ambiguity. Which is ironic , since the aim of localization is to reduce such confusion . A further interpretation, which extends also into the title text, is that these groups may have been supposed to meet on the same day. But even the committee that was supposed to fix these problems messed this up. Cueball may be 'explaining' the staggered approach to cover up that the two groups are already reading the date(s) for the meeting quite differently. ISO-8601 (that is, standard number 8601 as promulgated by the International Organization for Standardization since 1988) specifies a date format of YYYY-MM-DD (e.g., 2021-12-31), which results in dates being listed in chronological order when sorted stringwise. The ISO format is called " big-endian ", which refers to the fact that the most significant unit in the date (the year) comes first. The European format is instead " little-endian ", as the front-end value represents the finest possible distinction the date can convey - the particular day. The American format is " middle-endian ", or occasionally "mixed-endian", since the value given first is the one which is neither the one with greatest significance nor the most precise. In the above, the 'value groups' are not usually internally checked for ' endianness ', but regular numerals are also usually written with the largest place values on the left – for example, the first 2 in 2021 is the thousands place – though whether this convention is big-endian or little-endian depends on whether the writing system of such numbers is in the context of left-to-right or right-to-left text. The concept of endianness is most often used in reference to the storage order, whether of indivisible binary bits or of values built up of successive value groups. Pairs of hexadecimal values are individually usually represented in big-endian 'numeric' order, where bitwise distinctions are not necessary, but it is useful to know if a system stores a multibyte value in big-endan or little-endian packing, i.e., whether the value 0x01 0x02 (values 1 and 2, on their own) is treated as a value of 258 (0x01*256 + 0x02*1) or 513 (0x01*1 + 0x02*256). (The term was taken in inspiration from a Jonathan Swift story about a war over which end of a boiled egg one should cut into, a useful metaphor for many other situations where diametrically opposed self-justifications for one or another practice may lead to standing by vague principles rather than agreeing upon a unifying resolution.) This standard was also mentioned in 1179: ISO 8601 and used in 1340: Unique Date . The joke in the title text is that it appears some people attempted to interpret the improperly formatted date as if it were expressed in the more ISO-8601 style of format of "Y/M/D". They read the date as 20 02, March 22, so they already went to their meeting almost 20 years ago. Unless the announcement of the meetings was made 2 decades in advance, there's a paradox that these participants would have taken the date from an announcement in the far future. However, a strict interpretation of the date would make this incorrect: ISO-8601 format specifies four-digit years (which also avoids having to assume the century), two-digit months, and two-digit days. Therefore "2/3/22” can by specification not be an ISO-8601 date, as "2" can only be rendered as "0002", and "3" must be "03". Even if the leading zeroes were omitted in violation of ISO-8601, the year would become Year 2 , not Year 2002. Since the standard always uses a 4 digit 'YYYY' format in the first field, and no common formatting uses YYYY-DD-MM, any date written in ISO-8601 is easily recognized and (comparatively) unambiguously interpretable as YYYY-MM-DD. Dates written as if Y-M-DD or other distortions should be considered formatted improperly, and unwisely. [A screen is shown which displays five rows of text, the top three above a dividing line. To the right of the screen the upper part of Cueball is visible as he delivers a message concerning the text on the screen:] Localization working group Upcoming meetings ----------------- US Team: 2/3/22 EU Team: 2/3/22 Cueball: And the European formatting and localization team will meet a month later...

Throat and Nasal Passages

Throat and Nasal Passages

https://www.xkcd.com/2563

https://www.explainxkcd.com/wiki/index.php/2563:_Throat_and_Nasal_Passages

[A graph with two curves are shown. The Y-axis ends in an arrow, but has no units or ticks. The X-axis has no arrow but has 23 ticks with every fifth longer and every tenth labeled. The first tick extends the Y-axis below the X-axis. Both curves start over the second tick and end over the last tick. One curve is a dotted straight line running along the bottom of the graph just above the X-axis. The other start a bit higher and oscillate a bit up and down with 19 sharp peaks and 19 troughs, where some of the troughs have extra features, and not all are equidistant. After this a 20th small peak just starts to drop down again, before the curve goes in to a very steep rise almost all the way to the top of the graph. There is a small dip on the way before it reaches a maximum. Then a deep drop followed by a smaller rise before an even deeper drop. But then at the end, the graph rises almost vertically to the highest point where the graph stops over the last tick. At the top left of the graph the two lines are explained showing a solid and a dotted line with text to their right. Below this, above the solid curve midway between the first two labels on the X-axis, is a label from which 5 arrows points to 5 consecutive peaks.] - How much Time I have spent thinking about my throat and nasal passages, over time ┅ How much I want to think about them Label:Cold/Flu Season X-axis: 2000 2010 2020

This comic is another in a series of comics related to the COVID-19 pandemic . This comic became the last to reference the pandemic for a long time. The next reference to COVID-19 came four months later and in 2615: Welcome Back it was just briefly mentioned in the title text. In the graph a black solid line displays how much he has been thinking about his throat and nose since 2000 and up until 2022. The first 20 years the graph oscillate up and down once every year, and every spike represents the common cold and flu season. Autumn and winter causes the spike, while spring and summer clearly drops. Perhaps this is indicating no tendency to suffer from hayfever , which might at least produce mini-spikes at the times of of maximum grass-pollen, tree-pollen and/or other similar atmospheric flotsam. There is basically a spike for every year, although some years it looks a bit different which could be variations induced by complex sociological or meteorological drivers - meeting more or fewer people inside stuffy buildings rather than in the open air. But all in all the peaks seem low, especially when compared to how much time he has thought about it since the COVID-19 pandemic broke out around March 2020. Each summer since there has been a dip, but not anywhere close to the tops of the previous years, and around New Year 2022 the graph peaks (likely due to the Omicron variant ). The peaks in 2020 and 2021 (2022) are about 6 times higher than those the year before 2020. So if the Y-axis begins at zero, this is how much more he thinks of his throat now than during the times when he actually had a cold. There seems to be no way of knowing if Randall has had COVID-19, but from his comics it seems safe to assume he is fully vaccinated. At the time of release the Omicron variant of COVID-19 seems to by-pass the protections given by vaccines for about 50% of those vaccinated, although vaccinated people generally do not experience severe symptoms. The joke is in the dotted line at the very bottom of the graph which either is just above zero, or is actually supposed to be the zero line (which would not change the above assumption about 6 times more thinking). This line reflects how much time he actually wishes to think about them, which is probably not at all. But even before corona Randall seems to have spent way too much time pondering his sore throat. In the title text Randall references the trick known as "You are now aware of your tongue", which is a self-fulfilling prophecy because it will make anyone hearing it involuntarily think and be aware of their tongue. In a much earlier comic, 972: November , this trick was the topic, see more about it there. Randall sarcastically remarks that the tongue trick needed an element of mortal peril to be truly enjoyable, as with the corona pandemic making him aware of his throat and nasal passages. His actual opinion is probably the opposite, that it was annoying before and that it only became worse now that it contains the danger of death. Being aware of your tongue is annoying, but not dangerous. Being aware of your throat during the COVID-19 pandemic may leave you fearing for your life, even if there is nothing wrong with your throat. Randall has before the corona pandemic complained about a sore throat caused by the common cold, see 1612: Colds , more than once just a few weeks apart, see 1618: Cold Medicine . See also 1896: Active Ingredients Only . [A graph with two curves are shown. The Y-axis ends in an arrow, but has no units or ticks. The X-axis has no arrow but has 23 ticks with every fifth longer and every tenth labeled. The first tick extends the Y-axis below the X-axis. Both curves start over the second tick and end over the last tick. One curve is a dotted straight line running along the bottom of the graph just above the X-axis. The other start a bit higher and oscillate a bit up and down with 19 sharp peaks and 19 troughs, where some of the troughs have extra features, and not all are equidistant. After this a 20th small peak just starts to drop down again, before the curve goes in to a very steep rise almost all the way to the top of the graph. There is a small dip on the way before it reaches a maximum. Then a deep drop followed by a smaller rise before an even deeper drop. But then at the end, the graph rises almost vertically to the highest point where the graph stops over the last tick. At the top left of the graph the two lines are explained showing a solid and a dotted line with text to their right. Below this, above the solid curve midway between the first two labels on the X-axis, is a label from which 5 arrows points to 5 consecutive peaks.] - How much Time I have spent thinking about my throat and nasal passages, over time ┅ How much I want to think about them Label:Cold/Flu Season X-axis: 2000 2010 2020

Sunshield

Sunshield

https://www.xkcd.com/2564

https://www.explainxkcd.com/wiki/index.php/2564:_Sunshield

[The James Webb Space Telescope (JWST) is floating through space, shown in white on a pitch black background. The two mirrors are seen in front of the sunshield, which is kite shaped. A white line goes from the telescope up to two lines of white text, connected with a small white line.] JWST: Okay, universe- JWST: Smile! [Same setting, but now only a small thin white line goes up to a line of white text representing a sound made by the telescope.] JWST: Click [Same setting, but now it turns out that a small bulb on the front of the telescope is a flash light. A bright flash glows from the bulb, turning most of the panel white. A cone on the left side is blocked and kept pitch black by the telescope's sunshield. The light fades a bit towards the edges of the picture, giving the light cone a rounded appearance. Thus the image actually looks a lot like Pac-Man in the process of eating the telescope.] [Caption below the panel:] Astronomy fact: The purpose of the JWST sunshield is to protect the Sun and the Earth from the telescope's powerful flash.

This is another comic with a Fact , though not a Fun fact - this time an Astronomy fact. The next comic with a fact, namely 2596: Galaxies , was also with an Astronomy fact. This is the first time that the field that a fact pertains to has been immediately repeated. JWST stands for James Webb Space Telescope , a space telescope that was launched 12 days prior to publication of this comic, see more details here 2559: December 25th Launch . It has a sunshield to protect its instruments from the heat of the sun and to keep them below 40 K (-233 °C/-388 °F). Deployment of the sunshield was completed the day before the comic was published. The JWST has to undergo a complex sequence of deployment steps to unfold parts that had to be packed tightly for launch. This sequence has 344 possible points of failure that would render the very expensive space telescope useless; 75% of them led up to the successful full deployment of the sunshield. Thus successful steps are widely celebrated, with this comic an example of such a celebration. Ordinary cameras use a flash to take pictures in low-light situations. Outer space is very dark [ citation needed ] (one of the JWST's mission objectives will help astronomers calculate exactly how dark ), so this comic posits that the JWST has a very powerful flash to compensate for this. Most astronomical cameras don't use flash photography [ citation needed ] -- they depend on the light either emitted by objects themselves (e.g., stars) or from nearby very bright objects (e.g., Solar System planets will reflect the Sun's light, while distant clouds of gas and dust may be largely illuminated by the light of supernovae or recently formed stars within or near them). A flash generally doesn't work for many reasons: There are some examples of astronomical research done using things similar to a flash. Radar astronomy involves emitting radio waves (microwaves) that bounce off distant planets, asteroids, comets, etc., and analyzing the returned waves. The Lunar Laser Ranging experiment uses lasers, which are loosely related to flashes for photography, to measure the distance between Earth and Moon. The outward light is concentrated upon the approximate area of the lunar target, which employs an optical trick to send most of that which actually struck it back to the approximate area of the source equipment. The comic assigns the sunshield a new, comical purpose of shielding the Sun (and Earth ,which is roughly in the same direction as the Sun, due to the deployment at the L2 Lagrange point ) from this flash, rather than the other way around. When the camera is taking a picture, the comic shows space in front of the shield lit up while there is a totally dark shadow behind the shield (in the direction of Earth and Sun). The comic also has the camera making a "click" sound. In traditional mechanical cameras without a mirror, this sound comes from the shutter opening and closing, and mirror-less digital cameras mimic this sound so the user (and subject, when human) knows when the picture is being taken. JWST won't actually click -- it doesn't have a shutter, as it takes long-exposure digital images, and in space no one can hear you click . The telescope also tells the universe to smile for the picture. The universe doesn't have a mouth to smile with [ citation needed ] , although there are a number of features both on Solar System objects and in deep space that look like faces; this is a phenomenon called pareidolia . The most well known is the Man in the Moon , but there are numerous others both in the Solar system , most famous is probably the Face on Mars and out among the galaxies, like the Cheshire Cat galaxy group named after the Cheshire Cat from Alice in Wonderland . The title text suggests that, due to the sunshield not being angled to shield Mars, Mars's surface has been badly scarred by the flash. This implies incredible strength of the flash, perhaps to ensure the light can return from its destinations, comparable to death-ray satellites in fiction. [The James Webb Space Telescope (JWST) is floating through space, shown in white on a pitch black background. The two mirrors are seen in front of the sunshield, which is kite shaped. A white line goes from the telescope up to two lines of white text, connected with a small white line.] JWST: Okay, universe- JWST: Smile! [Same setting, but now only a small thin white line goes up to a line of white text representing a sound made by the telescope.] JWST: Click [Same setting, but now it turns out that a small bulb on the front of the telescope is a flash light. A bright flash glows from the bulb, turning most of the panel white. A cone on the left side is blocked and kept pitch black by the telescope's sunshield. The light fades a bit towards the edges of the picture, giving the light cone a rounded appearance. Thus the image actually looks a lot like Pac-Man in the process of eating the telescope.] [Caption below the panel:] Astronomy fact: The purpose of the JWST sunshield is to protect the Sun and the Earth from the telescope's powerful flash.

Latency

Latency

https://www.xkcd.com/2565

https://www.explainxkcd.com/wiki/index.php/2565:_Latency

[Caption above a graph showing a bar with 6 lines between the two ends:] Typical process latency: [The bar is split in two small regions at either end with two times two lines close to each other at the left and only one of those pairs of lines near the right. In between is a very long white area with no features. Above the two small segments at either end, there are small brackets of this type "{" lying down so the tip points up towards a curved line that then goes up to two labels.] Left: Automated steps: 800 ms Right: Automated steps: 200 ms [A similar, but very long, bracket is below the bar indicating the long white area in the middle. The tip points down to a label:] Someone copies and pastes data from a thing into another thing: 2-15 minutes (More if the person on call is busy)

This comic is about the time it takes for a request to be processed; a total of 1 second is devoted to automated processes, but 2-15 minutes or longer are devoted to a not-yet-automated process that is performed by a human. Part of the humor comes from the fact that most, if not all, instances of a person copying and pasting data from one place to another could be trivially automated and included as part of the automated steps, if only a programmer could take the time to program the process. Having a human take several minutes to move data that a computer could move in fractions of a second is incredibly inefficient, and reflects the humorously poor optimization present in many routine processes. The title text refers to SCAPDFATIAT, which is defined in the comic as Someone Copies and Pastes Data From a Thing Into Another Thing. Because it requires a human worker to fully accomplish, in-between various other work commitments as well as possibly personal/non-work activities, it is plausible that (even if the copying was started promptly enough) the person involved will not have pasted onwards by the time their effective working day ends. It might be reasonable to assume that a job that ought to take no more than a few actual minutes thus is only 'guaranteed' to be concluded at some point the following working day (which may be a whole long weekend away, possibly including public holidays). The business will therefore state (e.g. in contractual service agreements) that the guaranteed response times are of the order of "within one working day". Even if they hope and expect that any request passed to their staff is handled within a much shorter timescale. If reliably capable of being fully automated (e.g. with a resilient and continually maintained server infrastructure), could be fulfilled almost instantly at any time of day or night. But it may be the need to keep an 'intelligent' human in the loop (as well as to "under-promise and over-deliver", rather than the reverse) that makes the concept of "next-working-day" a more attractive commitment to make. [Caption above a graph showing a bar with 6 lines between the two ends:] Typical process latency: [The bar is split in two small regions at either end with two times two lines close to each other at the left and only one of those pairs of lines near the right. In between is a very long white area with no features. Above the two small segments at either end, there are small brackets of this type "{" lying down so the tip points up towards a curved line that then goes up to two labels.] Left: Automated steps: 800 ms Right: Automated steps: 200 ms [A similar, but very long, bracket is below the bar indicating the long white area in the middle. The tip points down to a label:] Someone copies and pastes data from a thing into another thing: 2-15 minutes (More if the person on call is busy)

Decorative Constants

Decorative Constants

https://www.xkcd.com/2566

https://www.explainxkcd.com/wiki/index.php/2566:_Decorative_Constants

[A small panel only with text. Written as an excerpt from a mathematical text book. Begins with a number for an equation, then follows the equation written in larger letters and symbols. And below are explanations of each term in the equation. The μ has a bar over the top and the D has a double vertical line.] Eq. 4-15 T = 𝔻m 0 (r out - r in ) μ̅ T: Net rate m 0 : Unit mass (r out -r in ): Flow balance 𝔻, μ̅: Decorative [Caption below the panel:] Math tip: If one of your equations ever looks too simple, try adding some purely decorative constants.

This is another one of Randall's Tips , this time a Math Tip. Randall gives an example of a complex looking equation labeled 4-15: T = 𝔻m 0 (r out − r in ) μ̅ But since 𝔻 and μ̅ are "decorative", the equation can be reduced to T = m 0 (r out − r in ) Here T is the net rate, m 0 the unit mass and (r out − r in ) the flow balance. The decorative symbols can be interpreted as constants 𝔻 = μ̅ = 1, in which case the implied operations of multiplication and exponentiation make sense. The 𝔻 is double-struck ("blackboard bold", thus in the comic only the vertical line is double). Mathematicians, who are always searching for more symbols [ citation needed ] , have taken to distinguishing things represented by the same letter by using different fonts, such as 𝑑, 𝐝, 𝒅, 𝐷, 𝐃, 𝑫, 𝒹, 𝒟, 𝖉, 𝕯, ∂, 𝕕, and 𝔻. The double-struck font is easier to write on a blackboard than a proper bold letter and often represents a set, such as ℝ for the set of real numbers or ℂ for the set of complex numbers. 𝔻 can represent the unit disk in the complex plane, the set of decimal fractions, or the set of split-complex numbers. μ is the Greek lowercase mu and has many uses in mathematics and science. Here it has a bar, μ̅, which could indicate a number of things, including the complex conjugate. Intriguingly, μ is the symbol in statistics for the population mean, and the overbar represents the sample mean, so this could represent a random variable which is the average of a sample of means μ i of different populations in some larger ensemble of populations. Using a special version both of D and μ to even further spice up the formula all leads up to the math tip: If one of your equations ever looks too simple, try adding some purely decorative constants. Other examples of well known equations that are profound but look simple include E = mc 2 ( Special Relativity ), PV = nRT (the Ideal Gas Law ), F = ma ( Newton's Second Law ), V = IR ( Ohm's Law ), and G μν + Λ g μν = κT μν ( Einstein field equations ), and e πi +1 = 0 ( Euler's Identity ). Of these, only the Einstein field equations have been spiced up with decorative indices (which actually hide a system of ten nonlinear partial differential equations). In the title text Randall mentions the Drag equation , which is attributed to Lord Rayleigh . In fluid dynamics , the drag equation is a formula used to calculate the force of drag experienced by an object due to movement through a fully enclosing fluid. The equation is F d = ½ ρu 2 c d A . Here F d is the drag force, ρ the mass density of the fluid, u the relative flow velocity, c d the drag coefficient and A is the area. Randall jokes that the factor of ½ in the equation is meaningless and purely decorative, since the drag coefficients, c d , are already unitless and could just as easily be half as big thus leaving out the ½ in front of the equation. The ½ is thus just an example of a "decorative constant." The usual reason for including the factor of ½ is that it is part of the formula for kinetic energy that appears in the derivation of the drag equation, i.e. ½ ρu 2 . However, modern treatments are so condensed that this factor of ½ is often smuggled in with no explanation. Since we can choose the constants to be whatever we want, it could be possible to absorb the ½ into the drag coefficient c d , but that does not mean it is unmotivated, since it comes from the kinetic energy. Still, Randall quotes Frank White's Fluid Mechanics textbook, which two times calls it "a traditional tribute to Euler and Bernoulli." According to White, the factor of ½ rather comes from the calculation of the projected area of the object being dragged. Randall has brought up this point before, in his book, " How To " The line from White probably refers to renowned mathematicians Leonhard Euler and Daniel Bernoulli . Euler who is held to be one of the greatest mathematicians in history worked directly with Daniel and was a friend of the Bernoulli family , that produced eight mathematically gifted academics. Daniel Bernoulli is known for modifying the definition of vis viva (what we now call kinetic energy) from mv 2 to ½ mv 2 , as motivated by the derivation from the impulse equation. In 1741, he wrote [Define vis viva ] esse ½ mvv = ∫ pdx . That is, "define vis viva to be ½ mv 2 = ∫ p d x ," where p is the force (from pressione ) and d x is the differential of position (infinitesimal displacement). Today, this equation says that the kinetic energy imparted to an object at rest equals the work done on it. In the drag equation ½ ρu 2 represents the dynamic pressure due to the kinetic energy of the fluid, and hence the 1/2 makes sense to keep in the equation, and could thus easily be argued not to represent a decorative constant. The title text is pretty much word-for-word a repeat from Randall's book How To . In Chapter 11: How to Play Football , he misuses the drag equation, and mentions this fact in more depth, in a footnote. [A small panel only with text. Written as an excerpt from a mathematical text book. Begins with a number for an equation, then follows the equation written in larger letters and symbols. And below are explanations of each term in the equation. The μ has a bar over the top and the D has a double vertical line.] Eq. 4-15 T = 𝔻m 0 (r out - r in ) μ̅ T: Net rate m 0 : Unit mass (r out -r in ): Flow balance 𝔻, μ̅: Decorative [Caption below the panel:] Math tip: If one of your equations ever looks too simple, try adding some purely decorative constants.

Language Development

Language Development

https://www.xkcd.com/2567

https://www.explainxkcd.com/wiki/index.php/2567:_Language_Development

[Megan and Cueball are looking to the left at a baby with dark hair. The baby sits on the left side of a table in an elevated baby chair.] Megan: He's only 1, so he still mostly speaks proto-Indo-European. Megan: But we've heard a few Germanic words already, so Old English can't be far off. Baby: *Melg- Baby: *Pl(e)hk- Cueball: They progress so fast!

Megan and Cueball are having what could appear to be a typical conversation about her child's ability to learn languages really fast. But the comic mixes up the concept of learning a language and the development of languages over time. The joke comes from the a conflation of two different things. The conventional meaning of language development is the process by which infants begin to talk, that is to understand and produce intelligible speech. The field of language acquisition (sometimes called... language development) seeks to understand how baby humans are able to rapidly comprehend, internalize, and begin producing a new language so rapidly. Instead of starting with babbling , the first stage of normal language development, this baby's form of "language development" seems to be the linguistic form: going through all of the theoretical stages of the evolution of the English language, from Proto-Indo-European to Germanic to Old English. In comparative linguistics and historical linguistics , Proto-Indo-European is a theorized common ancestor of the Indo-European language family. Proto-Germanic is a reconstructed language formerly spoken in Iron Age Scandinavia. It developed out of Proto-Indo-European and is the proposed common ancestor for all Germanic languages . Old English would have developed out of Proto-Germanic. Modern English developed out of Old English with many additions from French (which comes from a different branch of the Indo-European language family). This parody of language development parallels the discredited theory of recapitulation in embryo development, sometimes expressed as "ontogeny recapitulates phylogeny", in which a developing animal embryo (ontogeny) was once thought to go through stages resembling successive adult stages in the evolution of the animal's remote ancestors (phylogeny). In linguistics, reconstructed words from proto-languages are commonly marked with an asterisk (*) to show that the word forms are not attested by any historical sources but created as a proposed ancestor word. The baby says the Proto-Indo-European roots that the words "milk" and "please" are derived from. Obviously, the speakers of Proto-Indo-European did not speak in roots, but used words made from the roots, so the way the baby talks does not reflect any stage of development of the proto-language. Some sounds babies make are hard to interpret. [ citation needed ] However, humans have a tendency to recognize known things and patterns. They see what they want to see and hear what they want to hear. Thus, a parent familiar with Proto-Indo-European may falsely hear their baby speak Proto-Indo-European by misinterpreting unintelligible sounds. Perhaps this is an alternate universe where every baby has to gradually develop their language skills along a historical path rather than a child-developmental one, until they reach the ultimately developed modern language of their parents (in this case Modern English). There have been alleged language deprivation experiments where newborn infants were not exposed to any spoken language in order to find the "natural human language", in the days before ethics review boards would have forbidden such cruel treatments. Such experiments are known today to be a source for psychological problems at least. Alleged outcomes in the apocryphal sources range from the deprived children imitating other sounds in their environment, to them dying. In the title text, Randall describes a 2-year-old child as speaking in iambic pentameter and in Elizabethan English, a meter and dialect of modern English used by Shakespeare more than 400 years ago. The Terrible Twos are a colloquialism referring to the developmental tendency of two-year-olds to have more temperamental behavior, as the child's developing assertion of autonomy and self-identity clash with other expectations of behaviour, before hopefully acceptably balancing their assertiveness with social normatism. The toddler's quote of "forsooth, to bed thou shalt not take me, cur!" would roughly be equivalent to "Indeed, you shall not take me to bed, you dog!" in less archaic English. [Megan and Cueball are looking to the left at a baby with dark hair. The baby sits on the left side of a table in an elevated baby chair.] Megan: He's only 1, so he still mostly speaks proto-Indo-European. Megan: But we've heard a few Germanic words already, so Old English can't be far off. Baby: *Melg- Baby: *Pl(e)hk- Cueball: They progress so fast!

Spinthariscope

Spinthariscope

https://www.xkcd.com/2568

https://www.explainxkcd.com/wiki/index.php/2568:_Spinthariscope

[Cueball is holding a small item up in on hand in front of his three friends. Megan has her arms lifted and bent in front of her, White Hat has his arms raised over his head and Ponytail is pointing at Cueball while her other hand, held down behind her, is balled into a fist.] Cueball: It's a spinthariscope, a 1940s toy with a radioactive isotope inside. If you let your eyes adjust to total darkness and look into the lens, you can see the flashes of individual atoms decaying. Megan: What?? White Hat: Aaaaa! Ponytail: Get it away! [Caption below the panel:] Fun fact: Spinthariscopes have the highest ratio of "that can't possibly be safe and legal" to actual safety and legality of any known toy.

This is another comic with one of Randall's fun facts . As stated in the comic, a spinthariscope is a device with a small amount of radioactive material ( americium or thorium ) and a screen. When one of the radioactive atoms decays, it emits an alpha particle , which strikes the screen, which emits a small flash of light. You can see these flashes by looking through a lens. It was invented in 1903 initially as a scientific instrument, but was soon replaced by more accurate and quantitative devices. But the original device was still popular for some time as an educational toy for children, and you can still get them today. The joke in the comic is that most people have little understanding of radiation, and overreact to any mention that something is radioactive. So when Cueball tells Megan, White Hat, and Ponytail that the toy contains radioactive material, they're shocked and scared. But the amount of radioactive material in the toy is very tiny and the radiation is itself so trivially contained that there's practically no risk from it. The short-ranged alpha particles are likely stopped by the lens through which the harmless flashes of light (from particles that instead hit and neutralise in the internal screen element) are seen. Alpha decay always leads to an unstable decay product, which results in further decay (always gamma decay, and sometimes beta decay as well) which are less easily blocked, but the amount of such radiation from these decay products is negligible. The fun fact in the caption says that Spinthariscopes have the highest ratio of "that can't possibly be safe and legal" to actual safety and legality of any known toy. When people hear about Spinthariscopes for the first time, they often assume, due to the radioactive material inside, that they must be very dangerous. They thus also question if such a toy is at all legal to make or own in the first place. But the fact is that Spinthariscopes are both safe and legal to make, sell and own. So, the perceived danger and presumption that it must be illegal is at a very high number, and the actual danger and the actual illegality results in a very low number on the same scale. It is this ratio between perceived and actual danger and illegality that are the highest for Spinthariscopes, higher than for any other known toy. The formulation, however, causes some confusion, because the caption uses actual safety and legality (high) instead of actual danger and illegality (low). Instead of a high ratio between perceived danger and actual danger, the result is an even ratio between perceived danger and actual safety, which are both high. The ratios for the other mentioned toys would also be even, as they have low perceived danger and low actual safety. This is obviously not the intended meaning, as the other toys are said to be toward the other end of the scale. The title text mentions some other materials/toys that sound dangerous but aren't. Gallium is a metallic element with a low melting point of 29.76°C (85.568°F) so it will melt in your hand. Additionally, gallium has strange properties when it interacts with aluminum, causing aluminum to "melt" or become brittle. Tritium is a radioactive isotope of hydrogen, but can be used to create glowsticks and other lighted objects. Though these two toys might seem dangerous, they are actually typically used perfectly safely. At the opposite end of the spectrum is lawn darts , a toy containing large darts that are thrown into the air to fall back down onto a target that's placed or marked upon the ground quite near the players' positions. Unlike the spinthariscope, which sounds dangerous but is actually harmless, lawn darts sound relatively innocent but can cause severe injury if you accidentally hit a person (and a few children were even killed ), so they were banned in the US and Canada in the 1980s. When sharpened, these toys even compare quite favorably to weapons of war . Today many houses have smoke detectors using ionization caused by radioactive decay of Americium-241 to detect the smoke. So having something with radioactive material in your house is quite common, and in this case increases the safety level for those houses. [Cueball is holding a small item up in on hand in front of his three friends. Megan has her arms lifted and bent in front of her, White Hat has his arms raised over his head and Ponytail is pointing at Cueball while her other hand, held down behind her, is balled into a fist.] Cueball: It's a spinthariscope, a 1940s toy with a radioactive isotope inside. If you let your eyes adjust to total darkness and look into the lens, you can see the flashes of individual atoms decaying. Megan: What?? White Hat: Aaaaa! Ponytail: Get it away! [Caption below the panel:] Fun fact: Spinthariscopes have the highest ratio of "that can't possibly be safe and legal" to actual safety and legality of any known toy.

Hypothesis Generation

Hypothesis Generation

https://www.xkcd.com/2569

https://www.explainxkcd.com/wiki/index.php/2569:_Hypothesis_Generation

[Miss Lenhart stands in front of a blackboard with various unreadable scribbles, gesturing towards it with a pointer.] Miss Lenhart: To do science, you generate a hypothesis, then test it. [Cueball is sitting at a desk, raising his hand.] Cueball: But how do you generate a hypothesis? [Miss Lenhart now stands in front of Cueball's desk, she is holding down the pointer and Cueball has his hands on his legs.] Miss Lenhart: Great question. How do you think you do it? Cueball: Well, maybe you - Miss Lenhart: And there you have it!

Miss Lenhart is teaching a science class and starts by formulating the fact that to perform any science you need to generate a hypothesis in order to test it. The front row student, Cueball (presumably the rest of the students in the class are off panel), is thus prompted to ask the salient question of how one finds an original hypothesis. By using a clever prompting question in reply, Miss Lenhart allows the student to discover the answer himself. In typical Miss Lenhart fashion she is a bit rude, interrupting him before he can even formulate his thoughts. But the idea that he even has gotten an idea to share is proof that he has made a hypothesis about how to generate a hypothesis. This does not, however, answer how he did it, but now he knows he can do it. This approach may not have worked with less eager/capable students, so it highlights the strengths of both the student and the teacher - and that she had a good understanding of the student's ability to reason this out with just the barest of guidance. Or perhaps it is just another prank by Miss Lenhart . The key aspect being conveyed in this simple exchange is that one of the many good practices in science (no matter the aspect, though the specifics may change according to the precise field of study) is that one should first have an idea of what you can test and then perform the test to confirm (or rule out) your idea. In the title text the joke is that it is thus very easy to make hypotheses and thus everyone makes them all the time, so there are numerous ones to test. And the now frazzled scientists that are trying to work their way through them request that everyone stop making new hypotheses until they have worked their way through the huge backlog of untested hypotheses already made. [Miss Lenhart stands in front of a blackboard with various unreadable scribbles, gesturing towards it with a pointer.] Miss Lenhart: To do science, you generate a hypothesis, then test it. [Cueball is sitting at a desk, raising his hand.] Cueball: But how do you generate a hypothesis? [Miss Lenhart now stands in front of Cueball's desk, she is holding down the pointer and Cueball has his hands on his legs.] Miss Lenhart: Great question. How do you think you do it? Cueball: Well, maybe you - Miss Lenhart: And there you have it!

Captain Picard Tea Order

Captain Picard Tea Order

https://www.xkcd.com/2570

https://www.explainxkcd.com/wiki/index.php/2570:_Captain_Picard_Tea_Order

[At the top of the panel, there is a large caption covering two lines with a sub-caption below in a normal-sized font:] Other words Captain Picard tried at the end of his tea order before settling on "hot" From most normal to least [Bellow this we see Picard, drawn bald except for a bit of hair near his ears and behind his head. He stands next to a machine, which is a standing rectangle of the same dimensions as Picard. In the front, there is an opening around the middle, a dispenser from where the ordered items can be retrieved. There is a label at the top of the machine. Picard is giving a command to the machine. His first three words are clearly spoken out as they stand, but then at the end of the sentence, instead of just adding one more word, there is a list of five words in a column between two gray lines. Five words are visible, but the top and bottom words are fading out, presumably other words are above and below, but no longer visible. All except the middle are gray. The middle word is placed as the direct follow up to the first three words in the sentence Picard speaks out, and this word is black like the previous three words. So this middle word is clearly the one he actually speaks out. The others were options, presumably on his mind.] Label: Replicator Picard: [To the left of the machine, a long arrow begins snaking its way towards the bottom, where it ends in an arrow pointing down towards the bottom of the panel. At the top, there is a broad and thick bar from which it starts. Beneath this there are several ticks, the first three are close together and on a part of the arrow that goes almost straight down. But then the arrow curves in under the drawing of Picard, and goes over another drawing of him, placed in a captioned frame. The arrow goes around this and up on the other side, where it goes around another drawing of Picard in a similarly captioned frame. After having gone around this frame it goes a bit up before turning almost straight down before the final arrowhead that points down. In total there are 36 labeled ticks on the arrow, see labels below. The ticks have very varying distances between them. There are especially long between them around the first panels with Picard, but closer together at the start and towards the very end. Above the top bar from where the arrow starts there is also a label and just below this and to the left of the long arrow is a smaller arrow pointing down in the direction of the long arrow. This small arrow has a label at its starting point.] Bar label: Normal Small arrow label: Less normal [The second drawing of Picard, shows him standing next to the labeled machine. Picard is this time holding a cup, with sticky lines connecting his hands and the machine to the cup. He clearly looks down at the cup rather than on the machine, as the hair behind his ear is turned differently than the first drawing, where he looks straight towards the machine. Above is a label inside a frame overlaid on the top line of the panel, with what Picard ordered:] "Tea. Earl Grey. Sticky." Label: Replicator [The third drawing of Picard, only displays him and not the machine. He is holding a vibrating cup in both hands and has now turned the other way, away from where the machine was in the previous drawings (again clearly seen by his hair). Very large letters are displayed in three lines behind him to the exclusion of all else. Four of the 15 letters are partly hidden behind the panel's frame, and seven of them are partly covered by Picard. Above is a label inside a frame overlaid on the top line of the panel, with what Picard ordered:] "Tea. Earl Grey. Loud." Teacup: Teeeeeeeeeeeeee [Words on the arrow from start to finish:] Hot Iced Decaf Good Lukewarm Tasty Boiled Watery Sour Meaty Solid Dry Raw Deep-fried Sticky Grilled Fossilized Magnetic Ballistic Unstable Blessed Blurry Loud Virtual Intravenous Expanding Ironic Segmented Verbose Cursed Unexpected Bipedal Afraid Infinite Tea for him, too

Captain Jean-Luc Picard is a primary character in the science fiction TV series Star Trek: The Next Generation , which is focused on the crew of a starship. The ship is equipped with replicators , which can create virtually any object or material requested, including food and drink, and which respond to verbal commands. In the show, Picard's beverage of choice is Earl Grey tea . His habitual method for ordering is to first specify what he wants (tea, in this case), then specify a particular type (Earl Grey), and then give specific instructions for how it is to be served (hot, as opposed to iced tea ). Because this is his favored drink, he repeatedly places the exact order " Tea. Earl Grey. Hot. " The first picture in the strip implies that the display shows each part of the order, and provides a list of options for the next step. Randall parodies this repeated order by suggesting other words that could follow "Tea. Earl Grey.", starting from ones he considers more "normal" moving to those he presumes increasingly "less normal" down a long and winding arrow. The results of two examples from the normal/less-normal scale are also illustrated: Sticky tea and loud tea. Sticky is kind of obvious, though perhaps not immediately understandable, the loud version is a tea that screams "Teeee..." The vibrating and screeching teacup may be a reference to the various Star Trek episodes about tribbles , which behave in a similar way in the presence of Klingons. The very last qualifying addition, the least normal is not a single word but "Tea for him, too." This reinterprets the meaning of the standard introductory words, suggesting that "tea", and "Earl Grey" are separate orders, which implies that he wants the replicator to produce tea, then replicate a human being named Earl Grey (either one of the Earls Grey or a person surnamed Grey with the given name of Earl), then a second tea to serve to this newly created person. Earl Grey tea is named after the Charles Grey, 2nd Earl Grey , a 19th century British Prime Minister, and Captain Picard possibly wishes to have said Earl be generated to provide him with company. In contrast to the often trivial use of a replicator as merely a potentially infinitely versatile vending machine, the comic sets up a number of quite esoteric options, culminating in Earl Grey himself potentially drinking (generic) tea, after both the tea and he have been replicated into existence by Picard. In the title text, someone tells Picard that they should wait until the Earl has been fully extruded from the dispenser, and then ascertain what he would actually wish to drink. The presumption is that it could take some time to get a full living person out of the replicator. This sort of operation would be better suited for the holodeck, which has been used to create simulacra of other historical figures, including Stephen Hawking, Albert Einstein, and Sir Isaac Newton, with the limitations that they are mere simulations without their own autonomy and cannot exist beyond the limits of the fixed holotransmitters; though at least two others seem to have gained full sentience, and granted (or be convinced they were granted) physical freedom. In the various versions of Star Trek , it's established that replicators aren't capable of producing living things , so canonically this version of the order could not be filled. [At the top of the panel, there is a large caption covering two lines with a sub-caption below in a normal-sized font:] Other words Captain Picard tried at the end of his tea order before settling on "hot" From most normal to least [Bellow this we see Picard, drawn bald except for a bit of hair near his ears and behind his head. He stands next to a machine, which is a standing rectangle of the same dimensions as Picard. In the front, there is an opening around the middle, a dispenser from where the ordered items can be retrieved. There is a label at the top of the machine. Picard is giving a command to the machine. His first three words are clearly spoken out as they stand, but then at the end of the sentence, instead of just adding one more word, there is a list of five words in a column between two gray lines. Five words are visible, but the top and bottom words are fading out, presumably other words are above and below, but no longer visible. All except the middle are gray. The middle word is placed as the direct follow up to the first three words in the sentence Picard speaks out, and this word is black like the previous three words. So this middle word is clearly the one he actually speaks out. The others were options, presumably on his mind.] Label: Replicator Picard: [To the left of the machine, a long arrow begins snaking its way towards the bottom, where it ends in an arrow pointing down towards the bottom of the panel. At the top, there is a broad and thick bar from which it starts. Beneath this there are several ticks, the first three are close together and on a part of the arrow that goes almost straight down. But then the arrow curves in under the drawing of Picard, and goes over another drawing of him, placed in a captioned frame. The arrow goes around this and up on the other side, where it goes around another drawing of Picard in a similarly captioned frame. After having gone around this frame it goes a bit up before turning almost straight down before the final arrowhead that points down. In total there are 36 labeled ticks on the arrow, see labels below. The ticks have very varying distances between them. There are especially long between them around the first panels with Picard, but closer together at the start and towards the very end. Above the top bar from where the arrow starts there is also a label and just below this and to the left of the long arrow is a smaller arrow pointing down in the direction of the long arrow. This small arrow has a label at its starting point.] Bar label: Normal Small arrow label: Less normal [The second drawing of Picard, shows him standing next to the labeled machine. Picard is this time holding a cup, with sticky lines connecting his hands and the machine to the cup. He clearly looks down at the cup rather than on the machine, as the hair behind his ear is turned differently than the first drawing, where he looks straight towards the machine. Above is a label inside a frame overlaid on the top line of the panel, with what Picard ordered:] "Tea. Earl Grey. Sticky." Label: Replicator [The third drawing of Picard, only displays him and not the machine. He is holding a vibrating cup in both hands and has now turned the other way, away from where the machine was in the previous drawings (again clearly seen by his hair). Very large letters are displayed in three lines behind him to the exclusion of all else. Four of the 15 letters are partly hidden behind the panel's frame, and seven of them are partly covered by Picard. Above is a label inside a frame overlaid on the top line of the panel, with what Picard ordered:] "Tea. Earl Grey. Loud." Teacup: Teeeeeeeeeeeeee [Words on the arrow from start to finish:] Hot Iced Decaf Good Lukewarm Tasty Boiled Watery Sour Meaty Solid Dry Raw Deep-fried Sticky Grilled Fossilized Magnetic Ballistic Unstable Blessed Blurry Loud Virtual Intravenous Expanding Ironic Segmented Verbose Cursed Unexpected Bipedal Afraid Infinite Tea for him, too

Hydraulic Analogy

Hydraulic Analogy

https://www.xkcd.com/2571

https://www.explainxkcd.com/wiki/index.php/2571:_Hydraulic_Analogy

[Miss Lenhart stands next to a white board with two diagrams while pointing to the first. While she is explaining Cueball interrupts her from off-panel as seen by his voice coming from the right side out of a starburst on the panels edge. The diagrams are a schematic circuit diagram and a water flow diagram. There is a battery (with labels on top and bottom) on the left and a resistor on the right of the circuit as well as labels on each of these and one at the top part of the wire. There is a pump to the left and a tighter section of the pipe to the right, as well as labels on these and on the top part of the pipe. At the bottom there is two arrow pointing in towards the pipe, this also has a label.] Miss Lenhart: Electric current is like water flowing in a pipe. The pressure represents- Cueball [off-panel]: Wait, hold on. Labels on circuit: + - V I R Labels on flow diagram: Pump F R D [The view changes so Miss Lenhart and the white board are seen from the side. She still stands next to the white board, arms now down, as Cueball approaches the board with a marker held in one hand. The diagrams can still be seen, but distorted from being viewed from the side, and no labels are readable.] Cueball: Do you mind if I just... [Zoom in on Cueball, who is drawing on the white board, which is the left edge of the panel, i.e. not visible in the panel. Noises from the marker drawing on the board comes up from the tip of the marker pen. The movement of the pen is indicated with small lines on either side.] Scribble Scribble Scribble [Miss Lenhart and Cueball, holding the marker pen down, stand on either side of the white board looking at Cueball's version with the merged diagram. He has connected the two, so instead of the wire going down after the resistor in the circuit diagram, it now is connected with water flowing to the right just below the resistor, and then up into the pump to the right of the resistor. At the bottom where the water pipe before bent up into the pump, the water now continues running to the left (the pipe was not drawn around it by Cueball), and it now flows where the bottom part of the wire, from the circuit, was before, turning up below the battery and connecting with it there. All the labels from before have been retained as follows.] Labels on diagram: + - V I R Pump F R D [Miss Lenhart and Cueball stand on a podium with a Cueball-like presenter. The presenter is holding two Nobel Prize medals up in his hands. He is holding them from the strings they are attached to, so the medals hang below his hands.] Presenter: And for the design and construction of the liquitricity device, the Nobel Prize goes to...

Electric flow is commonly represented by a " hydraulic analogy ". In this analogy, the water pressure represents voltage and the flow of the water is the current . Electric resistance is represented by a constricted section of a pipe. Miss Lenhart is teaching a class and starts to explain this analogy when Cueball suddenly has an idea and changes her diagrams - connecting the electrical diagram and the hydraulic diagram. In doing this, he has envisioned what comes to be called a "liquitricity device", combining liquid water and electric current flows together and given a suitably portmanteau title. The last panel shows that Miss Lenhart and Cueball eventually receive the Nobel Prize , presumably the Nobel Prize in Physics , for the design and construction of the device - indicating that rather than being purely theoretical it has actually been practical to make this device. The title text 'explains' how this device works and references Ohm's Law , one of the fundamental laws of electricity, but strangely seems as much an incomprehensible mix of the two as the diagram in explaining whatever form of possible duality it actually employs. One of the featured Footer comics , 730: Circuit Diagram , displays a very complex circuit diagram. Although no pump or direct water flow can be found here, it all ends up in a beaker with holy water. And there is a symbol labeled 3 liters, at the bottom close to the beaker. This is the symbol for an orifice or flow restriction used on plumbing or hydraulic diagrams. So Randall already mixed water flow and circuit diagrams over 10 years ago. [Miss Lenhart stands next to a white board with two diagrams while pointing to the first. While she is explaining Cueball interrupts her from off-panel as seen by his voice coming from the right side out of a starburst on the panels edge. The diagrams are a schematic circuit diagram and a water flow diagram. There is a battery (with labels on top and bottom) on the left and a resistor on the right of the circuit as well as labels on each of these and one at the top part of the wire. There is a pump to the left and a tighter section of the pipe to the right, as well as labels on these and on the top part of the pipe. At the bottom there is two arrow pointing in towards the pipe, this also has a label.] Miss Lenhart: Electric current is like water flowing in a pipe. The pressure represents- Cueball [off-panel]: Wait, hold on. Labels on circuit: + - V I R Labels on flow diagram: Pump F R D [The view changes so Miss Lenhart and the white board are seen from the side. She still stands next to the white board, arms now down, as Cueball approaches the board with a marker held in one hand. The diagrams can still be seen, but distorted from being viewed from the side, and no labels are readable.] Cueball: Do you mind if I just... [Zoom in on Cueball, who is drawing on the white board, which is the left edge of the panel, i.e. not visible in the panel. Noises from the marker drawing on the board comes up from the tip of the marker pen. The movement of the pen is indicated with small lines on either side.] Scribble Scribble Scribble [Miss Lenhart and Cueball, holding the marker pen down, stand on either side of the white board looking at Cueball's version with the merged diagram. He has connected the two, so instead of the wire going down after the resistor in the circuit diagram, it now is connected with water flowing to the right just below the resistor, and then up into the pump to the right of the resistor. At the bottom where the water pipe before bent up into the pump, the water now continues running to the left (the pipe was not drawn around it by Cueball), and it now flows where the bottom part of the wire, from the circuit, was before, turning up below the battery and connecting with it there. All the labels from before have been retained as follows.] Labels on diagram: + - V I R Pump F R D [Miss Lenhart and Cueball stand on a podium with a Cueball-like presenter. The presenter is holding two Nobel Prize medals up in his hands. He is holding them from the strings they are attached to, so the medals hang below his hands.] Presenter: And for the design and construction of the liquitricity device, the Nobel Prize goes to...

Alien Observers

Alien Observers

https://www.xkcd.com/2572

https://www.explainxkcd.com/wiki/index.php/2572:_Alien_Observers

[Three aliens are looking at a screen. They each have six tentacles, of which four are used as legs, and the other two can be used as arms. They also have a small mouth and two eye stalks with a large eye at the end of each. The eyes has large eyelashes all the way around. One of the aliens is standing to the left of the screen, pointing to it by raising one of its tentacles. The other two aliens stand to the right of the screen looking at the picture. The screen's image depicts a cross-sectional diagram showing two humans in a rough landscape. There is a shaded area above each of the humans and the terrain. The shaded area's boundary consists of arcs of differing sizes centered upon each human. To the left of the first human there is also a small straight area over the ground. To the left of this towards the edge of the screen, what appears to be an arc with a very large radius that begins and rises high up compared to the other two arcs, around a point beyond the on-screen image's edge. The rightmost human's zone has a dashed region between concentric radii of different sizes indicating that this zone has been revised further out than before. Four flying-saucer like spaceships are shown in the air close to, but above, the shaded areas. One high near the left curve, one over the flat area, one near the intersection between the two small arcs and one over the middle of the right arc.] Left Alien: Human 38XT11-B-C54 just bought a new phone with a 10x zoom, so we have to expand our restricted flight zone by 1,800 meters to keep our ship blurry. Right Alien 2: Seriously? Didn't they just upgrade? Left Alien: I know, I know... [Caption below the panel:] The hardest part of being an alien observing Earth is keeping track of what cameras everyone has.

This strip depicts a group of aliens observing earth, and discussing their "restricted flight zone", which they appear to change each time a human acquires a more powerful camera. This comic was followed directly by 2573: Alien Mission , where aliens use similar looking flying-saucer type spacecrafts to observe Earth. It is not specifically stated that these two form a series, but the next comic could be seen as a direct follow up to the this one, indicating that the aliens are the same in the two comics. Just 7 comics later 2579: Tractor Beam also used similar spacecraft. Both strips are based on UFO conspiracy theories , which are common in the US and a number of other countries. It is often claimed that Unidentified Flying Objects seen in the sky are, in fact, extraterrestrial space craft, visiting earth for various reasons. Reports of such sightings have existed for a long time, and ever since cameras became widely available, photographs (and later videos) have been produced which are claimed to show such flying vessels. Almost invariably, these images are sufficiently distant, blurry, or otherwise obscured as to make any kind of detailed identification impossible - they could not be Unidentified Flying Objects if it were possible to identify them! This strip lampoons such ideas by positing that aliens are real, but deliberately maintain a distance such that no clear photographs can be taken. While this concept might seem initially plausible, it doesn't stand up to examination. Over the past several decades, cameras have become far more common, with most of the population of many countries carrying cameras every waking moment (and even sleeping with those same cameras within reach). At the same time, cameras available to the average consumer have dramatically increased in resolution and zooming capabilities. The same shot that resulted in blurry and vague photographs in early digital photography could result in much more detailed images today, and also overcome many of the pitfalls associated with 'analogue' photography without sufficient skill and/or bulky equipment. What's more, the cameras owned by individual consumers have a wide range of resolutions and other capabilities, meaning that an image that would show little detail from one person's camera could result in highly detailed photograph if someone else took a picture. The fact that improving camera technology has not resulted in improved images of these supposed vessels is an impossibly weak point in these conspiracy theories. The humorous premise of the strip is that these aliens are real, and are monitoring earth, but are taking deliberate actions to keep evidence of their presence ambiguous. To do this, they would need to not only monitor what camera technology exists on earth, but the exact type of camera each individual owns, and maintain their flights right at the outer visual limit of those cameras. Such information would need to be implausibly detailed, and constantly updated, because technology is constantly improving and people are constantly getting new phones with new cameras. Part of the joke is that the aliens would have to know the visual range of our cameras, but instead of remaining safely outside of it (so that no pictures of their vessels could be taken at all), they stay close enough to be seen, but never close enough for detailed images. In a broader sense, this strip addresses the same issue as previous strips, such as 718: The Flake Equation and 1235: Settled , in which the phenomenon of UFO sightings/reports is still left not resolved (either way) despite what modern technology should suggest is possible. The suggestion is that this trend either means that sufficiently advanced aliens are deliberately leaving ambiguous evidence of their presence, or that no such alien visitors are here, and the purported evidence is either faked, or misinterpretations of other phenomena. It's pretty clear which explanation Randall favors. In the title text, the aliens note that one particular human now has a YouTube account, meaning they are likely to record video instead of attempting to capture still images. This means that the alien craft used to create the sighting must behave as erratically as possible, in order to avoid being identified. This relates to the often wildly oscillating (as well as blurry) films and videos of 'UFOs' that have been taken by the impromptu human observer beyond the limit of their ability to hold their fully-zoomed camera steady. Here it is explained as the flying saucers actually moving in an improbably jerky manner to prevent detailed recording of their craft. Further briefings of the sort depicted would doubtless accompany upgrades in optical/digital-stability features or the purchase of a camera tripod. The identifier for the one buying the phone begins with "Human 38XT11". This seems likely to be a reference to THX 1138 as this was the title of George Lucas 's first film, which is also referenced in the original Star Wars film. The name contains the number in reverse, as well as the letters, if "human" could be written as H. [Three aliens are looking at a screen. They each have six tentacles, of which four are used as legs, and the other two can be used as arms. They also have a small mouth and two eye stalks with a large eye at the end of each. The eyes has large eyelashes all the way around. One of the aliens is standing to the left of the screen, pointing to it by raising one of its tentacles. The other two aliens stand to the right of the screen looking at the picture. The screen's image depicts a cross-sectional diagram showing two humans in a rough landscape. There is a shaded area above each of the humans and the terrain. The shaded area's boundary consists of arcs of differing sizes centered upon each human. To the left of the first human there is also a small straight area over the ground. To the left of this towards the edge of the screen, what appears to be an arc with a very large radius that begins and rises high up compared to the other two arcs, around a point beyond the on-screen image's edge. The rightmost human's zone has a dashed region between concentric radii of different sizes indicating that this zone has been revised further out than before. Four flying-saucer like spaceships are shown in the air close to, but above, the shaded areas. One high near the left curve, one over the flat area, one near the intersection between the two small arcs and one over the middle of the right arc.] Left Alien: Human 38XT11-B-C54 just bought a new phone with a 10x zoom, so we have to expand our restricted flight zone by 1,800 meters to keep our ship blurry. Right Alien 2: Seriously? Didn't they just upgrade? Left Alien: I know, I know... [Caption below the panel:] The hardest part of being an alien observing Earth is keeping track of what cameras everyone has.

Alien Mission

Alien Mission

https://www.xkcd.com/2573

https://www.explainxkcd.com/wiki/index.php/2573:_Alien_Mission

[Two 'classic' Flying Saucer spacecraft are hovering in the sky with speech-lines indicating communication from someone within each saucer. The rightmost is tilted a bit, like it is being attentive to the left.] Left Saucer: Sir, can we talk? Left Saucer: We've been observing earth for almost a century. [Same setting but both saucers are level.] Left Saucer: Hovering and zooming from place to place, trying to avoid being spotted by humans. Right Saucer: Yeah. [In a Frameless panel only the left saucer is shown. The right saucer's voice emerges from an edge-of-panel starburst.] Left Saucer: By now we've flown over every inch of the surface many times. Right Saucer (off-panel): Yes? And? [Same setting as in the first panel, with the right one tilted towards the left saucer.] Left Saucer: Face it: If Bigfoot is real, he's not anywhere on this planet. Right Saucer: But humans have captured some intriguing videos! Left Saucer: *sigh* Right Saucer: How else do you explain the...

This comic followed directly after 2572: Alien Observers , both comics featuring alien flying saucers observe Earth. It is not specifically stated that these two form a series, but this comic could be seen as a direct follow up to the previous one, indicating that the aliens are the same in the two comics. Just 6 comics later 2579: Tractor Beam also used similar spacecraft. The comic portrays a conversation between aliens inside two flying saucers (or alternately, two aliens whose form is that of flying saucers) in which they discuss their long-secret observation of Earth. It seems that the leader of the mission is in the right saucer, as the alien in left saucer begins by saying "Sir, can we talk". The left alien then continues to state that they have been secretly observing Earth for almost a century (perhaps from the early 1930's or late 1920's, and the title text suggests they already were there in 1937). During these almost 100 years, they have repeatedly flown over every (square) inch of Earth's surface, while trying to avoid being spotted by humans. (This is related to the previous comic, which is about improving cell-phone cameras making it increasingly difficult for flying saucer occupants to avoid being photographed.) This leads up to the punchline, which reveals that the leader in the right saucer has been hunting for Bigfoot . The left alien tells him that if a Bigfoot exist anywhere in the universe, it is not on planet Earth. Apparently even advanced aliens have been unable to spot Bigfoot. The alien leader continues his delusion by citing intriguing human videos of something that looks like Bigfoot. When the other alien sighs, implying that this conversation has occurred many times before, the leader continues his arguments with the typical conspiracy line, "How else do you explain the..." The first panel alludes to the fact that UFO sightings became commonplace only in the 1940s . The humor derives from the fact that UFO enthusiasts and cryptozoology enthusiasts have a similar mindset: They both believe in phenomena that the scientific establishment believes baseless. Both systems are fully lacking in clear evidence but have an abundance of eyewitness accounts and vague/blurry photographic evidence. And both belief systems have existed for many years, but rapidly advancing technology, accumulating data, and ubiquity of high quality cameras have still failed to capture any clear and detailed evidence. ( Randall seems to find this point particularly significant, and although his previous comic explained the bad flying saucer photos, he already made the comic 1235: Settled long ago, where he calls it settled that Bigfoot, UFOs, and similar phenomena don't exist since everyone has a camera handy at all times.) While these concepts are parallel, they're logically independent, as one deals with species that are presumably native to Earth and the other deals with advanced alien species visiting the Earth. The notion of alien visitors being interested in cryptozoology is incongruous: to them, all Earth animals would presumably seem equally alien. In previous strips, Randall has suggested playing conspiracy theories off against one another (see 966: Jet Fuel ). This comic has a similar theme: suggesting that UFOs are here to search for Bigfoot (and the Yeti) sounds ridiculous on its face. But any explanation of why it's ridiculous would apply equally well to the notion of Bigfoot and UFO's individually. Some of the aliens clearly have a similar belief, at least in Bigfoot, which is why they came to Earth. This implies that they had some prior knowledge or suspicion of its existence, and only then possibly narrowed it down to this one planet because of the videos humans have made. Whatever the arguments about Bigfoot, the title text reveals a separate discussion regarding the Yeti , a similar large hominid purported to reside in the Himalayas , and the tentative permission to conduct one last search for it. As the Yeti and Bigfoot are very similarly described, they could also be seen as the same, so the only difference is that finding a Bigfoot in the Himalayas would make it a Yeti. In the discussion about this last search, they caution about staying high above the Pacific and watch where they are going. This is because, as it turns out, they were the cause of the Amelia Earhart incident. Amelia Earhart disappeared while flying over the Pacific Ocean in 1937 and neither her nor her plane have ever been found. The title text implies that she disappeared because of an encounter with a flying saucer. She has previously been the main character in 950: Mystery Solved and has since been a recurring theme on xkcd. That their clearly superior observation technology and methods have been apparently unable to resolve these issues at first seems like it shouldn't bode well for our own cryptozoologists. But since lack of results does nothing to deter them, and since it is always impossible to prove a negative, they would likely not change their beliefs even if they heard of the alien results: "Bigfoot of course hides when the aliens look! And how else do you explain the..." [Two 'classic' Flying Saucer spacecraft are hovering in the sky with speech-lines indicating communication from someone within each saucer. The rightmost is tilted a bit, like it is being attentive to the left.] Left Saucer: Sir, can we talk? Left Saucer: We've been observing earth for almost a century. [Same setting but both saucers are level.] Left Saucer: Hovering and zooming from place to place, trying to avoid being spotted by humans. Right Saucer: Yeah. [In a Frameless panel only the left saucer is shown. The right saucer's voice emerges from an edge-of-panel starburst.] Left Saucer: By now we've flown over every inch of the surface many times. Right Saucer (off-panel): Yes? And? [Same setting as in the first panel, with the right one tilted towards the left saucer.] Left Saucer: Face it: If Bigfoot is real, he's not anywhere on this planet. Right Saucer: But humans have captured some intriguing videos! Left Saucer: *sigh* Right Saucer: How else do you explain the...

Autoresponder

Autoresponder

https://www.xkcd.com/2574

https://www.explainxkcd.com/wiki/index.php/2574:_Autoresponder

[Cueball and White Hat are talking to each other while Cueball is typing on his smartphone. A dark-haired figure stands behind White Hat, drawn with thicker/rougher lines as if clad in bulky clothing; wearing spiky knee and elbow guards, a spike-embossed and notably scarred crash-helmet upon its head; and is holding a glinting sharp sword in its hand.] Cueball: Ready to go? White Hat: Yup! Can you email me the tickets before we leave? Cueball: Sure, one sec. [The next panel is nested inside the first, although at first it just looks like two individual panels. This could indicate the second panel is an immediate response to the first. The armored figure aggressively moves forward towards Cueball, who drops his phone in surprise. The armored figure has its sword-arm raised, the other hand pushing White Hat behind it, by pushing him in the face which causes him to stumble backwards so his hat starts to fall off.] Cueball: Okay, I sent it to- Armored figure: It is outside work hours! Armored figure: Prepare to die! Cueball: Augh! [Caption below the panel:] I always feel bad when I trigger my friends' work autoresponders.

Cueball and White Hat are going to some kind of show (a movie or concert, perhaps), and Cueball asks White Hat if he is ready to go, who affirms this but asks for Cueball to email him the tickets before they go. When Cueball does this he apparently opts to send them to White Hat's work email address. When White Hat is not at work, he has an autoresponder activated that tells people to not disturb him as he is not at work. Usually this means that his email server sends an automatic response telling the sender of the mail that he is not at work, and not to expect an immediate reply. But in this comic, White Hat has a physical autoresponder standing behind him, drawn as a human with thicker/rougher lines as if clad in bulky clothing, wearing spiky knee and elbow guards and a spike-embossed and notably scarred crash-helmet upon its head. It holds a glinting, sharp sword in its hand. When Cueball inadvertently activates it, it plunges forward to 'defend' White Hat from being disturbed by work related things during his spare time. It is so aggressive that it even violently pushes White Hat out of the way, with a blow to the face so that he falls back and dislodges his hat, as it prepares to confront the perpetrator, Cueball. In the caption below, Randall states that he feels bad when he activates his friends' autoresponders. It is unclear if this is because he thinks he disturbs them with what they might think is work, because he then knows he will not get a reply or if he feels attacked (like Cueball in the comic) by their "aggressively worded" auto-replies. In the title text Cueball shouts out (in all caps) to the autoresponder "I admire how you set boundaries and I hope your colleagues respect them! Please spare my life!" He therefore thinks it is a good idea to have time away from work where you cannot be contacted by your colleagues. It is unclear if the autoresponder is a human or a robot, but the open-faced helmet reveals the fringe and neck-length hair generally seen on female characters, although for instance Megan 's hair is usually longer and not so messy as this creature. This would be reminiscent of the Android series , especially 600: Android Boyfriend , where one of the androids moves past its owner. [Cueball and White Hat are talking to each other while Cueball is typing on his smartphone. A dark-haired figure stands behind White Hat, drawn with thicker/rougher lines as if clad in bulky clothing; wearing spiky knee and elbow guards, a spike-embossed and notably scarred crash-helmet upon its head; and is holding a glinting sharp sword in its hand.] Cueball: Ready to go? White Hat: Yup! Can you email me the tickets before we leave? Cueball: Sure, one sec. [The next panel is nested inside the first, although at first it just looks like two individual panels. This could indicate the second panel is an immediate response to the first. The armored figure aggressively moves forward towards Cueball, who drops his phone in surprise. The armored figure has its sword-arm raised, the other hand pushing White Hat behind it, by pushing him in the face which causes him to stumble backwards so his hat starts to fall off.] Cueball: Okay, I sent it to- Armored figure: It is outside work hours! Armored figure: Prepare to die! Cueball: Augh! [Caption below the panel:] I always feel bad when I trigger my friends' work autoresponders.

What If? 2

What If? 2

https://www.xkcd.com/2575

https://www.explainxkcd.com/wiki/index.php/2575:_What_If%3F_2

[Randall, drawn as Cueball, is throwing his arms out as he stands next to a big red book with white drawings on the cover. The cover shows a large passenger plane that has just taken off, as can be seen since the landing gear still has the wheels extended (only one wheel is visible at the middle part and then the one in the front). A Tyrannosaurus Rex has jumped on to the plane and it is biting down on the ceiling of the plane a bit in front of the wings, as if on the back of a prey. The dinosaur has already broken through the ceiling. Below is a jagged landscape with small mountain like peaks in the background. Megan and Cueball are standing on the top of the second of two raised plateaus, looking up at the plane and dinosaur. There is unreadable white text above the plane, then a title beneath the plane, and the authors name below the landscape, and more unreadable text beneath that, all in white. Below the book, there is a small arrow pointing to the right bottom of the book, with a label beneath.] Randall: Announcement: I’m publishing a what if? sequel! Book cover: what if? 2 Book cover: Randall Munroe In stores 9/13, available for preorder now: xkcd.com/whatif2 [Randall is shown holding up his smart phone in one hand. The screen lights up as indicated with small lines at the top. These point up to at least six SMS texts, each with two lines of text. They are shown in speech bobbles with a small arrow in the bobbles lower left corner. All six are covered partly by either the other five, or by Randall’s head, and none of them can be read in any meaningful way; only parts of sentences or words are clearly visible. The bobbles and the text in them are all drawn in gray. Randall is narrating (not speaking) in this panel, both above the SMS texts, and below.] Randall narrating: Ever since I wrote what if? , I’ve been flooded with questions. Randall narrating: And not just from readers- My friends and family stated texting them to me, too. Text 1: Hey, could s.. ele Text 2: Hypothe… Text 3: If you s… Jupiter… Text 4: Could my c… or… Text 5: Do you… my car… Text 6: If I trie… the sun, would I… Randall narrating: Honestly, I love it. [Randall is again standing next to his red book talking. There is also a second version of the book lying to the right of the closed book, and this has been opened up to reveal two pages. The text is unreadable and the images are very hard to see, but it seems that two people are standing next to each other on the right page. The image at the top of the left page has been enlarged and shown to the right of the open book. It is an image of the Earth that is being peeled by a potato peeler, which takes off a large peel from the north part of Scandinavia and then goes via Russia into Asia. The title and author name can still just be read on the book,but maybe only because they are already known...] Randall: The questions are so good. People have asked about touching exotic materials, traveling across space and time, eating things they shouldn’t, and smashing large objects into the Earth. There are questions about lasers, explosions, swingsets, candy, and soup. Several planets are destroyed-one of them by the soup. Book cover: what if? 2 Book cover: Randall Munroe [Zoom in on the top part of Randall speaking on.] Randall: Like the first book, what if? 2 also features collections of short answers, new lists of weird and worrying questions, and some of my favorite answers from the What if site. [Only the closed red book are shown in this panel, in an even larger version than in any of the previous panels. But it is still only the title and the author name that can be read, but in this version these can also be read on the spine of the book. Randall is narrating again, and there are text both above and below the book.] Randall narrating: If you want to get it when it’s released, you can preorder a copy at xkcd.com/whatif2 Book spine: what if? 2 Randall Munroe Book cover: what if? 2 Book cover: Randall Munroe Randall narrating: Available Sep 13, 2022

This comic is Randall 's way of announcing and promoting his new book, what If? 2 , based on his what if? blog and following his first what if book. The entire comic (including the xkcd Header text ) is a link to a what if? 2: the book page on xkcd . Apart from promoting the book, the comic also explains why he ended up writing a sequel. After the first book came out Randall was flooded with what if? questions. Presumable mainly from his readers via e-mail, but his friends and families also started texting him with these questions. Some of these texts are displayed in the comic, but only partially, so none of the six question texts can be read. But where one might think that this would become tiresome, Randall instead tells the readers the opposite: "Honestly, I love it." He then continues to praise the quality of the questions, mentioning no less than nine examples of what the questions were about. And in the process ensures the reader that planets, including the Earth, will be destroyed multiple times in his new book. At the end he lets the readers know that some of the features of the first book, with short answer sections and disturbing questions (likely not answered), are also included in this book. He also states that a few of his favorites from the What If? site site have been included, so it is not all new material. From the book stores, it seems like he includes his very last online What If? ( Earth-Moon Fire Pole ) for instance, which was released on 2018-05-21, almost four years before this comic was released. Also, by the time the book is released, it will be almost four years and four months since the last article on What If? The final part of the comic is a picture of the book that both makes it clear when the book is released and how to preorder it. Randall ensured the maximum possible attention to his announcement by placing a countdown in the header about three weeks prior to the announcement. This has caused a lot of speculation as to what would be revealed on the day of this comic's release 2022-01-31. The timer was inside a panel at the top right of the xkcd header text next to the standard header text: xkcd updates every Monday, Wednesday, and Friday . Inside the panel a picture began emerging after the first day, but the picture only changed approximately once every four hours. After a few weeks was it certain that it was a plane that was being revealed. And on the second to last day, around day twenty, it was clear that it featured a T. rex -like dinosaur en silhouette standing on top of the aircraft, apparently trying to eat its way into the fuselage, and it might have been possible to guess the relation to the What If? sequel. On the day before the announcement on xkcd, however, Amazon made visible a preorder page for the book , so the answer was made clear about a day before Randall had intended. This clearly annoyed users of this page as can be seen in the talk page for the countdown . Until then, however, there were numerous theories about the countdown and what the image would reveal as the image gradually changed throughout the eventual 136 frames . In the title text, Randall feels that he must clarify the release day (as in 2562: Formatting Meeting ), since he has often joked about the way different countries (and people) write dates. He did not use the one version he himself had promoted in earlier comics. He does however give two different versions of the release date: the first is "9/13" in the first panel, which is at least (usually — see below) only readable one way; harder to misinterpret is the more expansive "Sep 13, 2022" in the final panel. A format that he could have used to avoid any confusion is: "the book is released on 2022-09-13," using the international standard as defined in the ISO 8601 standard and shown in 1179: ISO 8601 . The clarification reads: By 9/13, I mean September 13th, not the 9th day of Jancember, the cursed 13th month that exists between December and January in the transdimensional temporal plane. Since there are only 12 months in the year, [ citation needed ] 9/13 actually cannot be mistaken, while 9/12 might be. So there was really no need for this clarification, especially with the last text in the last panel. So this is of course just a title text joke, where he can manage to make a portmanteau of January and December ("Jancember") and then then call this a cursed month as it would be the 13th month if it came before New Year. This comic came out at the end of January, so it could have been at the end of Jancember instead. The number thirteen is seen by many as an unlucky number, so a thirteenth month would be considered cursed by some, or at least unlucky. In reality, a 13th month can exist in some alternate calendars and is then called " Undecimber ". At the release of this comic, the header changed to promote the website, the xkcd links in the top left section of xkcd was changed to promote the book and he made his first Blag post in more than two years with the What If 2 post. The what if? header was also changed to accommodate promotion of the new book; not so strange, seeming as it was based on that blog. A picture is displayed at the top with the book at both ends and this text in between, with the first line taking up the top and the two other lines below, the first in a frame: What If? 2 Preorder now On sale 9/13 The entire picture links to the what if? 2 page. Exactly two months after the release of this promotion comic Randall made another comic about his new what if? 2 book: 2600: Rejected Question Categories . In this he also gives the release day as 9/13, in the title text, although without any mention of the ambiguity of this date format. [Randall, drawn as Cueball, is throwing his arms out as he stands next to a big red book with white drawings on the cover. The cover shows a large passenger plane that has just taken off, as can be seen since the landing gear still has the wheels extended (only one wheel is visible at the middle part and then the one in the front). A Tyrannosaurus Rex has jumped on to the plane and it is biting down on the ceiling of the plane a bit in front of the wings, as if on the back of a prey. The dinosaur has already broken through the ceiling. Below is a jagged landscape with small mountain like peaks in the background. Megan and Cueball are standing on the top of the second of two raised plateaus, looking up at the plane and dinosaur. There is unreadable white text above the plane, then a title beneath the plane, and the authors name below the landscape, and more unreadable text beneath that, all in white. Below the book, there is a small arrow pointing to the right bottom of the book, with a label beneath.] Randall: Announcement: I’m publishing a what if? sequel! Book cover: what if? 2 Book cover: Randall Munroe In stores 9/13, available for preorder now: xkcd.com/whatif2 [Randall is shown holding up his smart phone in one hand. The screen lights up as indicated with small lines at the top. These point up to at least six SMS texts, each with two lines of text. They are shown in speech bobbles with a small arrow in the bobbles lower left corner. All six are covered partly by either the other five, or by Randall’s head, and none of them can be read in any meaningful way; only parts of sentences or words are clearly visible. The bobbles and the text in them are all drawn in gray. Randall is narrating (not speaking) in this panel, both above the SMS texts, and below.] Randall narrating: Ever since I wrote what if? , I’ve been flooded with questions. Randall narrating: And not just from readers- My friends and family stated texting them to me, too. Text 1: Hey, could s.. ele Text 2: Hypothe… Text 3: If you s… Jupiter… Text 4: Could my c… or… Text 5: Do you… my car… Text 6: If I trie… the sun, would I… Randall narrating: Honestly, I love it. [Randall is again standing next to his red book talking. There is also a second version of the book lying to the right of the closed book, and this has been opened up to reveal two pages. The text is unreadable and the images are very hard to see, but it seems that two people are standing next to each other on the right page. The image at the top of the left page has been enlarged and shown to the right of the open book. It is an image of the Earth that is being peeled by a potato peeler, which takes off a large peel from the north part of Scandinavia and then goes via Russia into Asia. The title and author name can still just be read on the book,but maybe only because they are already known...] Randall: The questions are so good. People have asked about touching exotic materials, traveling across space and time, eating things they shouldn’t, and smashing large objects into the Earth. There are questions about lasers, explosions, swingsets, candy, and soup. Several planets are destroyed-one of them by the soup. Book cover: what if? 2 Book cover: Randall Munroe [Zoom in on the top part of Randall speaking on.] Randall: Like the first book, what if? 2 also features collections of short answers, new lists of weird and worrying questions, and some of my favorite answers from the What if site. [Only the closed red book are shown in this panel, in an even larger version than in any of the previous panels. But it is still only the title and the author name that can be read, but in this version these can also be read on the spine of the book. Randall is narrating again, and there are text both above and below the book.] Randall narrating: If you want to get it when it’s released, you can preorder a copy at xkcd.com/whatif2 Book spine: what if? 2 Randall Munroe Book cover: what if? 2 Book cover: Randall Munroe Randall narrating: Available Sep 13, 2022

Control Group

Control Group

https://www.xkcd.com/2576

https://www.explainxkcd.com/wiki/index.php/2576:_Control_Group

[Ponytail is looking at her smartphone which she is holding in her hand, while she is talking to Cueball.] Ponytail: Are you playing Wordle? Cueball: No, I'm in the control group. [Caption below the panel:] My new all-purpose excuse for when I'm not doing something

Wordle ( [1] ) is a web-based word puzzle game that was popular when this comic was released. In the comic, Ponytail asks Cueball whether he's playing the game; Cueball replies that he isn't, because he's "in the control group". In scientific studies, the control group stands in opposition to the treatment group; whereas the treatment group receives the experimental "treatment", the control group does not, instead receiving a placebo or nothing at all. This is done to establish a baseline—what would happen without intervention—against which the result of the experimental treatment is compared later. When Cueball replies that he's "in the control group", this implies that Ponytail and other Wordle players are part of a "treatment" group. This implies that playing Wordle may have some long-term effects worth studying. Jokingly, this may also imply that Wordle is some sort of social experiment , perhaps a sociological study conducted by Harvard . As noted in the caption to the comic, Randall has been using this line as his new all-purpose excuse when he is not doing something. It's a clever way of saying that you're determined not to take part, as a control group requires him to avoid it. Mind control studies can also be nonconsensual experiments that massively impact public behavior. More realistically, Cueball may be part of a real market research control group, which was not exposed to advertisements and memes supporting the game or anything associated with the game. Market research studies have been common since the advent of advertising. The title text is a parody of Wordle's sharing feature, which users have been posting on Twitter or other social media platforms to show their success or failure at the game. The title text shows a 5x6 grid, but calls it "Placeble" (a portmanteau of Placebo and Wordle) and has a number after it, suggesting that not only is the game a social experiment, but that a "placebo version" is being given to the control group. In the real Wordle sharing feature, the number represents the current day's game. On the date this comic was released, the Wordle website itself was on game 228, matching the number in the title text. Randall's placebo version of Wordle has blank/incorrect squares and has a score of "x/6" which is a loss in Wordle — unsuccessful after the maximum 6 tries. [Ponytail is looking at her smartphone which she is holding in her hand, while she is talking to Cueball.] Ponytail: Are you playing Wordle? Cueball: No, I'm in the control group. [Caption below the panel:] My new all-purpose excuse for when I'm not doing something

Sea Chase

Sea Chase

https://www.xkcd.com/2577

https://www.explainxkcd.com/wiki/index.php/2577:_Sea_Chase

[A pirate ship flying the Skull and Crossbones is sailing after a merchant ship. Two sailors' voices come from the merchant ship.] Merchant ship sailor #1: They're closing in! Merchant ship sailor #2: Hang on, we're almost at the meridian! [A map of the Earth in the Robinson projection, with two red dots in the middle of the Atlantic Ocean. A voice comes from the red dot further to the east.] Merchant ship sailor #2: Now! Throw the switch! [In a frameless panel, Cueball, representing merchant ship sailor #1, pulls down a giant lever switch labeled "Projection", from "Robinson" to "Goode Homolosine".] [A map of the Earth in the Goode Homolosine projection, with one red dot on the American side of the split and one red dot on the European side of the split.]

In this comic, Randall returns to one of his pet subjects: map projections . Unusually, [ citation needed ] this time it is from the perspective of people living — or, in this case, sailing — upon the world that is quite literally being mapped. Two sailing ships, of circa 18th-century design, are engaged in a close chase across the Atlantic , the aggressor flying the Skull and Crossbones of a stereotypical pirate vessel. It can be seen from the flags of both ships that they are tacking into the wind, the trailing ship seeming to be lighter and yet deploying more effective canvas with two active sails than the forward one can with three. The ship being chased has a plan to escape and the means to do so. At a crucial moment, Cueball is told to flip a large incongruous switch that (like several other artifacts in the xkcd universe) alters the nature of their reality. Whereas beforehand the world is directly represented upon a simply contiguous map, the Robinson projection , it is now changed to one (which is actually the new reality) known as Goode Homolosine in which the flattening of the world mitigates localized warping of angle, distance, and area by introducing discontinuities in relatively "unused" parts of the mapped world, such as the center of the Atlantic. By precisely timing the change (as they cross a particular meridian , possibly the 40°W one), they leave the pursuer now on the wrong side of the very real gap, allowing the pursued ship to escape whatever fate they were trying to avoid. Though there is still an oceanic connection, it requires sailing down the edge towards the tropics, rounding this particular rent in the planet's surface, and heading back up the other side. This is vastly further than Cueball's ship needs to travel to reach (presumably) any European port in which they can safely moor. The title text elaborates on the policies of the ship: crewmates are never to look into the "projection abyss" and to never hit the red button labeled " DYMAXION ." The first rule suggests that changing the projection of physical reality produces a gap in reality — a void. This may be dangerous to gaze into or simply unnerving to crewmates, hence the rule. This may also be a reference to a well-known quote by philosopher Friedrich Nietzsche : “He who fights with monsters must take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you.” See Beyond Good and Evil at Project Gutenberg The second rule references a button that seems to do the same thing as the lever but changes the world into a Dymaxion projection . The Dymaxion map projects the Earth onto 20 triangles, which are typically chosen such that landmasses are contiguous while adding many discontinuities in the oceans. This would make navigating by ship in such a 2D world even more difficult than in the Goode homolosine projection. In particular, crossing the Atlantic ocean becomes impossible because of the introduction of a projection abyss from Norway to the Caribbean. The Robinson, Goode Homolosine, and Dymaxion projections have been referenced in 977: Map Projections . [A pirate ship flying the Skull and Crossbones is sailing after a merchant ship. Two sailors' voices come from the merchant ship.] Merchant ship sailor #1: They're closing in! Merchant ship sailor #2: Hang on, we're almost at the meridian! [A map of the Earth in the Robinson projection, with two red dots in the middle of the Atlantic Ocean. A voice comes from the red dot further to the east.] Merchant ship sailor #2: Now! Throw the switch! [In a frameless panel, Cueball, representing merchant ship sailor #1, pulls down a giant lever switch labeled "Projection", from "Robinson" to "Goode Homolosine".] [A map of the Earth in the Goode Homolosine projection, with one red dot on the American side of the split and one red dot on the European side of the split.]

Sword Pull

Sword Pull

https://www.xkcd.com/2578

https://www.explainxkcd.com/wiki/index.php/2578:_Sword_Pull

[Cueball walks towards a large stone on the ground from which the hilt of a sword is protruding. The ground he walks on is uneven, with small plants growing and small stones lying on the ground.] Cueball: ?? [Cueball stands on the stone and attempts to pull the sword out of the stone using both hands and leaning a bit back away from the sword.] [Cueball manages to pull the sword partially out of the stone, still using both hands, and now he is almost standing in full height, but still leaning a bit back. Both he and the sword is vibrating from the effort, as indicated by several sets of two lines around the sword and Cueball's arms. The pull gives off a loud sound, and also a buzzing sound comes because of the pull. And three small lines above the right part of the stone indicated that other sounds are coming from the stone] Pull: Yank! Sword: Zzz z z Stone: Put put put Stone: Brrr rr rr [Cueball is still holding on to the sword, with the tip still inside the stone. But he is not pulling anymore and is now looking down on the stone beneath him. There are now several lines from both sides of the stone indicating noises coming from the stone, which now is written on both sides of Cueball on the stone.] Cueball: ?? ?? Stone: Rr r r rrrrrrrr r r [Cueball has released the sword which has then returned to the original position deep in the stone. The stone is now clearly moving to the right of the panel, with Cueball on top of it. He is looking behind him and holding his arms out to the side to keep his balance. The patch where the stone lay to start is dark. Four large lines behind the stone indicates how it is moving. The stone is already partially outside the right edge of the panel. The sound from the stone is floating behind the stone as it moves to the right] Stone: R r r r rrrrrr r rr

A surprised Cueball walks up to a stone where apparently a sword is stuck in almost to the hilt, embedded in a stone much like a particularly well-known fable in the legends of King Arthur . This may mean this sword is called Excalibur . Usually, the narrative is that the one who can free the significant sword becomes king of England (or, technically, Britain), see for instance Disney's The Sword in the Stone — or the scene as featured in 1521: Sword in the Stone , where Megan decides to return the sword back into the stone after reading about England on Wikipedia. (It has been commented that the one who managed to embed the sword in the stone in the first place may have had the greater skill and/or strength.) Cueball rises to the challenge and stands atop the stone, for leverage, and pulls hard to yank it almost out of the stone. With a surprise even greater than before, he finds that the pulling of the sword merely starts a motor within the stone and, almost immediately, the whole assemblage starts moving to the right with Cueball still standing upon it. Having failed to fully remove the sword from the stone, after he releases it the sword is retracted back to its original position inside the now moving stone. The title text implies that the sword is actually the rope starter for Merlin's dirt bike . Merlin , a wizard, is typically known as King Arthur's mystical advisor. The title text mentions that Merlin really should not just let his dirt bike lie around, indicating that this is a common occurrence and has caused problems before. Since rocks are usually not dirt bikes in disguise, [ citation needed ] Randall may be describing this literally, as in a stone-bike that travels through the dirt, as it appears to represent in the last panel. Some similarly-sized stones, namely sailing stones , do move spontaneously with up to 0.3 km/h in precise conditions. However, the stone in the comic appears to be moving at a higher speed, and sailing stones require no rope starting. [ citation needed ] [Cueball walks towards a large stone on the ground from which the hilt of a sword is protruding. The ground he walks on is uneven, with small plants growing and small stones lying on the ground.] Cueball: ?? [Cueball stands on the stone and attempts to pull the sword out of the stone using both hands and leaning a bit back away from the sword.] [Cueball manages to pull the sword partially out of the stone, still using both hands, and now he is almost standing in full height, but still leaning a bit back. Both he and the sword is vibrating from the effort, as indicated by several sets of two lines around the sword and Cueball's arms. The pull gives off a loud sound, and also a buzzing sound comes because of the pull. And three small lines above the right part of the stone indicated that other sounds are coming from the stone] Pull: Yank! Sword: Zzz z z Stone: Put put put Stone: Brrr rr rr [Cueball is still holding on to the sword, with the tip still inside the stone. But he is not pulling anymore and is now looking down on the stone beneath him. There are now several lines from both sides of the stone indicating noises coming from the stone, which now is written on both sides of Cueball on the stone.] Cueball: ?? ?? Stone: Rr r r rrrrrrrr r r [Cueball has released the sword which has then returned to the original position deep in the stone. The stone is now clearly moving to the right of the panel, with Cueball on top of it. He is looking behind him and holding his arms out to the side to keep his balance. The patch where the stone lay to start is dark. Four large lines behind the stone indicates how it is moving. The stone is already partially outside the right edge of the panel. The sound from the stone is floating behind the stone as it moves to the right] Stone: R r r r rrrrrr r rr

Tractor Beam

Tractor Beam

https://www.xkcd.com/2579

https://www.explainxkcd.com/wiki/index.php/2579:_Tractor_Beam

[A flying saucer type spacecraft hangs in the air above a flat area with scattered rocks and two hills in the background. A beam of 'light' emerges, a conical region textured with wavy lines radiating along its length, from a small square opening beneath the bottom of the craft going down to the ground a bit right of the saucer where its conceivably circular cross-section is rendered elliptic by both its angle of projection and our own viewing perspective. Cueball hangs suspended within the middle of the beam, above the ground but still some way from the saucer. His arms are held out to either side and his legs are bent up behind him. He is looking up at the saucer while talking.] Cueball: Does this beam only lift me? How do you avoid pulling up dirt and leaves and stuff? If I kick off my shoes, will they fall? Cueball: Is my weight pulling your ship downward? What will happen if a bat flies through the beam? Cueball: Hey, why does your ship have those blinky lights? Are they... [Caption below the panel:] Moments later, the aliens set me back down and left.

Cueball is being pulled into a spaceship by a beam of light, called a tractor beam in the title. This is a common trope in science fiction, and usually pretty scary for the person involved. However, while Cueball is being pulled up, he asks a series of questions about the beam, about the force on the ship, and about the ship itself. The punch line is the caption - the aliens, frustrated by Cueball's questioning, release him and move on, to presumably find a different human to abduct and study. Many people have reported being abducted by aliens in real life, though none of these have been confirmed. [ citation needed ] The first three questions deal with the properties of the beam – how it can be controlled to pull only him (and his clothes), not anything else. He also wonders whether the beam would still continue to lift his shoes if he took them off midway. Perhaps his apparel is only rising with him because it normally stays attached to him, perhaps it is similarly levitated with equal force or impulse. Theoretically, it could only lift his clothing, with enough force to hoist him along with it, though if this was done with insufficient finesse, it could cause damage to the clothing or the person. (One might be tempted to call this a Space Wedgie .) It is highly unlikely that this type of tractor beam could be used on Cueball without him realizing it, which would likely lead to him asking how the tractor beam lifted the clothes and not him. Next, Cueball asks if his weight is pulling the ship downward. This would be the case, for example, if he were hoisted upwards by a rope instead of the beam, as equal but opposite forces act against each other, but not if the beam alters the nature of his surroundings such as with Cavorite or another means of gravitational shielding or alteration. Then he asks what will happen if a bat flies through the beam. Things that could happen include the beam breaking (and him falling downward) due to the projected effect being interrupted, the bat being pulled up ahead of him as it enters the effective volume of the levitating beam or else nothing at all as it is outside the actual volumetric segment of the beam that is more than ambient light-effects. It may presumably have a relationship with the same focal effect as that which avoids the ground upon which he previously stood being drawn upwards. Also, the shadow of the bat on the ground might make the light beam look like an inverted Bat-Signal . As the ship leaves, Cueball continues asking questions, as shown in the title text. Those questions address the shape of the ship. He asks whether the aliens based the saucer shape on depictions of extraterrestrials in earth popular culture, or if classic flying saucers were inspired by them. His next question was cut off, but what we heard is "does the rotational symmetry help with". Whether Cueball actually arrived onboard the ship is uncertain. If he started badgering the aliens with questions during the lift and then (as stated) was immediately set down again then he did not. Either way, they got fed up and decided to return him to the ground instead of sharing their knowledge, or just because they preferred someone less talkative. They may prefer or expect more scared, overawed, or surprised abductees but, by whatever alien criteria they judge their catches, it seems he isn't what they want. This was the third comic in less than three weeks featuring aliens using this type of flying saucer type spaceship. The other two comics were in a row just 6 and 7 comics before this one, 2572: Alien Observers and 2573: Alien Mission [A flying saucer type spacecraft hangs in the air above a flat area with scattered rocks and two hills in the background. A beam of 'light' emerges, a conical region textured with wavy lines radiating along its length, from a small square opening beneath the bottom of the craft going down to the ground a bit right of the saucer where its conceivably circular cross-section is rendered elliptic by both its angle of projection and our own viewing perspective. Cueball hangs suspended within the middle of the beam, above the ground but still some way from the saucer. His arms are held out to either side and his legs are bent up behind him. He is looking up at the saucer while talking.] Cueball: Does this beam only lift me? How do you avoid pulling up dirt and leaves and stuff? If I kick off my shoes, will they fall? Cueball: Is my weight pulling your ship downward? What will happen if a bat flies through the beam? Cueball: Hey, why does your ship have those blinky lights? Are they... [Caption below the panel:] Moments later, the aliens set me back down and left.

Rest and Fluids

Rest and Fluids

https://www.xkcd.com/2580

https://www.explainxkcd.com/wiki/index.php/2580:_Rest_and_Fluids

[Cueball and Black Hat are talking to each other. Black Hat has his arms outstretched.] Black Hat: So glad you're feeling better! Black Hat: Be sure to get dehydrated and run on a treadmill until you black out! [Caption below the panel:] Once people aren't sick anymore, it's important to remind them to stop resting and drinking fluids.

Black Hat congratulates Cueball on his recovery from some type of illness or injury. Common advice when someone is sick is to get plenty of rest and drink lots of water, to aid recovery and to ensure they don't ignore various common causes of fluid loss. However, being Black Hat, he targets Cueball (who has been restored to full health) to tell him that he now should do the opposite of this. While a healthy person should get a reasonable amount of exercise, and should not spend excessive time in bed, Black Hat goes to an absurd extreme. He tells Cueball to stop drinking water entirely and engage in an excessive amount of activity — in this case, by running on a treadmill to the point of physical collapse. The caption explains this, saying that it is "important" to tell people who have recently recovered from sickness to stop resting and drinking fluids, suggesting that these behaviors are for the exclusive purpose of healing and that they are useless (or even counter-productive) for someone who is now healthy. Part of the joke may be that the most basic common and basic advice to people who are sick is good, general advice in any case. While a person who's sick should be particularly attentive to these needs, and will generally require more rest than a person who's healthy, getting adequate rest and hydration are important for maintaining health, not just recovering from illness, and pursuing the opposite would be dangerous. The title-text expands on this backward line of thinking by suggesting to do the opposite of common remedies for various usual remedies: a hot cloth, standing, breathing parched air, taking histamines (this is as opposed to reducing fever with a cool compress, resting in bed, inhaling hot water vapors and using antihistamines ). These are increasingly bizarre. A hot cloth on the forehead would range from useless to dangerous (if too hot, it could cause burns or overheating). Remaining standing isn't harmful for most people, but would soon become exhausting. Breathing dry air isn't harmful for most people, but without adequate water would dehydrate you even faster. Histamines are compounds created in the body that regulate the immune system. They're generally not available as a supplement so it would be difficult to "take" histamines. If you could somehow raise your histamine levels artificially, it could interfere with any number of bodily functions. This comic has some resemblance to 2279: Symptoms since it also makes a joke out of symptoms or the opposite of symptoms. Although not mentioned here, this comic is probably, like Symptoms, related to the COVID-19 pandemic , as many people were still sick with it at the time of publishing this comic. [Cueball and Black Hat are talking to each other. Black Hat has his arms outstretched.] Black Hat: So glad you're feeling better! Black Hat: Be sure to get dehydrated and run on a treadmill until you black out! [Caption below the panel:] Once people aren't sick anymore, it's important to remind them to stop resting and drinking fluids.

Health Stats

Health Stats

https://www.xkcd.com/2581

https://www.explainxkcd.com/wiki/index.php/2581:_Health_Stats

[Cueball is looking down and to the right at his bent arm, where a small device is radiating as shown with several small lines. Above him the message from the device is shown in a frame, that is divided in two by a line. The top part has one line of text, with a x at the end for closing the message. And below in the second half are two lines of text. Cueball is speaking to someone off-panel, who replies from a starburst at the panel's edge.] Box title bar: New health stat! Box: Left hand blood volume: 21.83 mL Cueball: Oh. Cool. Not sure how to interpret that, but good to know, I guess. Off-panel voice: I guess! [Same setting but Cueball has turned to the left, still looking at his device on his bend arm. The message on the device is now only showing the message part, so it is no longer divided into two parts.] Box: Left hand blood volume: 21.81 mL Cueball: Huh, it's going down. I guess that happens. Off-panel voice: Mhm. [In a frame-less panel, Cueball now has both arms bent with his hands close together in front of him. He has once again turned toward the right, and is still looking at the device.] Box: Left hand blood volume: 21.86 mL Cueball: Oh weird, now it's going up higher than before. Off-panel voice: Maybe you shouldn't look at- [Cueball now holds his arm with the device outstretched towards the right, with his other arm bent in front of him a finger raised.] Box: Left hand blood volume: 22.09 mL Cueball: It's going way up! Is my hand exploding?! Cueball: And now my pulse is rising! Aaaaa!!!! Off-panel voice: So sorry. We will treasure your memory.

Cueball's has a smartwatch that tells him a new health statistic. It is clearly either a new watch or a newly discovered feature added to his existing one. It seems to monitor the volume of blood currently in his left hand (specifically the one the watch is being worn on the wrist of, implying it tracks the inflow and outflow and maintains a running tally) and conveys this quantity in milliliters (ml). It also tracks other stats like his pulse, as seen later, but this is not what currently interests Cueball. Instead he studies the blood volume information and finds it changing from moment to moment. This may be from a combination of his pulse (misaligned to the frequency of the updates) or the vertical position and attitude of his hand (he subtly changes the hand's position from panel to panel). It could just be inaccuracies in the data, an issue with all scientific instruments but more so for consumer devices used without practiced expertise - it is unlikely he has strapped the measuring device tight enough onto his wrist to give scientifically consistent results, even with such slight arm movements as he makes. He reports his thoughts on this to someone off-panel, who is heard replying to all his comments. At first, Cueball just voices the assumption that the small change is normal, and accepts the movement away from a number he had no reason to disbelieve as realistic. But then two measurements in a row both increase. Although all the changes are slight, compared to the magnitude of the numbers themselves, this freaks him out. He may be extrapolating these two data points into the future - if this rather selective trend continues, his hand may explode from its ever-increasing volume of blood. Either this, or Cueball noticed that the variation in the first three data points was ±0.025, but the final variation suddenly surpasses this level by ten times this range, massively redefining his evolving expectations. For whatever reason he becomes anxious, a consequence of this is that his pulse also begins to rise, as also documented by the watch. This could simultaneously increase his blood pressure (not noted as being another monitored statistic) and in turn causing another rise in the volume of blood in his hand. Knowledge of the pulse increase makes him even more alarmed, which will cause a positive feedback loop at least in the short term. The total difference between the maximum (22.09 ml) and minimum volume (21.81 ml) of blood in his hand is only 0.28 ml compared to an average of 21.9 ml, so less than 1.5% difference. This can realistically be assumed to be a normal fluctuation from heartbeat to heartbeat and/or with change of posture. For that matter, neither Cueball nor ourselves may have any idea what a normal volume of blood in his left hand would be. His comment in the first panel is that he's "not sure how to interpret" the initial measurement, and it might need rather uncommon medical knowledge to do so - even those who have learnt how much blood a typical human body should contain might be stumped by how much of that is just within a typical (or specific) human hand. However, he seems to have assumed that 21.83 ml was a normal measurement simply since it was the first one he saw (a stereotypical preference for early information ). Just before his anxiety reaches breaking point, his off-panel friend begins to tell him to stop looking at the watch all the time, but is interrupted mid-sentence by Cueball actually freaking out. This final outbreak causes his off-screen companion to tease him by saying that "We will treasure your memory", thus joking that Cueball will soon die from the blood loss when his hand explodes. The title text continues with this teasing where the friend jokes that after his demise he will live on forever in his friends' hearts. From there he will thus also be responsible for pushing a bit more blood into his friends' left hands, now and again, so they can feel this as a squeeze to remind them of how they lost their friend to a left-handed blood explosion. This is likely meant to parody the tendency of people to monitor minute details of their own health, pandered to by possibly misguided developments in personal meditech, without having a clear idea of what any of the data means. This is arguably much more common today with health devices readily available, which can give the average person data about their own body but often don't offer useful context. Cueball is apparently sufficiently fixated on data that apparent changes to any metric causes him to panic. He doesn't know what the blood volume of his hand means for his health, or even whether it's a useful metric, yet he obsesses over perceived trends in the data. The irony is that his very focus causes a more important metric (his pulse rate) to elevate. This may be intended to suggest that excessive fixation on one's own health can cause elevated anxiety. Ironically, this stress can potentially be more harmful than the things that the person has become upset about. [Cueball is looking down and to the right at his bent arm, where a small device is radiating as shown with several small lines. Above him the message from the device is shown in a frame, that is divided in two by a line. The top part has one line of text, with a x at the end for closing the message. And below in the second half are two lines of text. Cueball is speaking to someone off-panel, who replies from a starburst at the panel's edge.] Box title bar: New health stat! Box: Left hand blood volume: 21.83 mL Cueball: Oh. Cool. Not sure how to interpret that, but good to know, I guess. Off-panel voice: I guess! [Same setting but Cueball has turned to the left, still looking at his device on his bend arm. The message on the device is now only showing the message part, so it is no longer divided into two parts.] Box: Left hand blood volume: 21.81 mL Cueball: Huh, it's going down. I guess that happens. Off-panel voice: Mhm. [In a frame-less panel, Cueball now has both arms bent with his hands close together in front of him. He has once again turned toward the right, and is still looking at the device.] Box: Left hand blood volume: 21.86 mL Cueball: Oh weird, now it's going up higher than before. Off-panel voice: Maybe you shouldn't look at- [Cueball now holds his arm with the device outstretched towards the right, with his other arm bent in front of him a finger raised.] Box: Left hand blood volume: 22.09 mL Cueball: It's going way up! Is my hand exploding?! Cueball: And now my pulse is rising! Aaaaa!!!! Off-panel voice: So sorry. We will treasure your memory.

Data Trap

Data Trap

https://www.xkcd.com/2582

https://www.explainxkcd.com/wiki/index.php/2582:_Data_Trap

[Cueball is sitting in an office chair at his desk, hands on his knees, looking at his laptop. Megan stands behind him, with her arms raised to the sides and above her head.] Cueball: Hey, look, we have a bunch of data! I'm gonna analyze it. Megan: No, you fool! That will only create more data!

Cueball wants to analyze a "bunch" of data that he has, likely from a survey or study. Megan warns him against doing analysis because analysis produces more data — specifically, data about the data . This is implied to be a bad thing, as in, having "too much" data is undesirable — perhaps he will be expected to analyze the metadata, then analyze the metadata created by the metadata, and so on. However, data generated from analysis may provide useful insights about the original data set, e.g. finding trends or correlations between data points. Avoiding the analysis or deleting its data could deprive the analyzer of useful information. And, in the case that the analysis is flawed or impossible, there is little danger in disposing of any resulting reports. [ citation needed ] The title text proposes an alternate solution: destructive analysis. It is important that the method chosen to analyze the data destroys as much information as it created, thus keeping the total amount of data constant. This expands on the concept of not having a surplus of data, suggesting that any analysis should destroy as much data as it produces. This would make data constant in quantity or in an equilibrium; of course, data doesn't actually have this limitation, [ citation needed ] and the user can create as much data as is needed or desired. In the quantum world information can neither be destroyed or created; see the no-hiding theorem , for instance. Destructive analysis is a term used in archeology; as the name implies the thing that you study is destroyed by the analysis. However, destructive analysis is rarely or never used to study data. [ citation needed ] [Cueball is sitting in an office chair at his desk, hands on his knees, looking at his laptop. Megan stands behind him, with her arms raised to the sides and above her head.] Cueball: Hey, look, we have a bunch of data! I'm gonna analyze it. Megan: No, you fool! That will only create more data!

Chorded Keyboard

Chorded Keyboard

https://www.xkcd.com/2583

https://www.explainxkcd.com/wiki/index.php/2583:_Chorded_Keyboard

[Cueball is sitting in an office chair at his desk, typing on his keyboard as shown by small lines over one hand, while looking at the screen of his stationary computer. The screen is on a raised platform on his desk. Lyrical text is written upon each scene, presumably what Cueball is typing.] I heard there was a secret chord That David pressed and it typed a word [A closeup on Cueball in a slim panel. We see him from the waist up, with his hands on the keyboard just beneath the panels frame.] But you don't use a chorded keyboard, do you [Same setting as in the first panel, except Cueball's arms have moved and there are movement lines above and below his arms.] It goes like this, <control> and <shift> The other hand hits H and <left> [Slimmer panel but same setting as in the first panel, again the arms have moved a bit, with movement lines above them. The final written word of text is marked as arising directly from the computer.] And all at once it types out Computer: Hallelujah

This strip is a parody of the first verse (and in the title text, the end of the last verse) of Leonard Cohen 's " Hallelujah ", which has become a distinctive and popular song of which covers and versions exist. Written as a ballad , it is partly based upon the allegory of a mystical musical chord of several musical notes, that the words and tune both describe and illustrate by example. Here is the verse from the song (see the lyrics here ): Now I've heard there was a secret chord That David played, and it pleased the Lord But you don't really care for music, do ya? It goes like this, the fourth, the fifth The minor fall, the major lift The baffled king composing "Hallelujah" Cueball is filking upon this theme, but in his case he has somehow set up his computer so that, upon pressing a certain combination of multiple keys on his keyboard, the system will automatically type out the word "hallelujah" (xkcd's all-caps lettering makes it unclear how the word is capitalized). In his description of the process, in both the comic proper and the title text, he uses adapted lyrics that again both describe and illustrate by example. Most of the initial lyrics are floating 'thoughts'. The punchline "hallelujah", however, is 'spoken' out of his computer monitor - typical of how on-screen text is indirectly shown in this comic series. It partially continues as a song parody through the title text but then trails off into a typical computer-complaint that he perhaps may often have cause to make . The original lyrics rely upon typically nuanced rhymes, such as "do you" (or "do ya'") with "Hallelujah", and "fifth" with "lift", but fairly reliably rhymes "chord" with "Lord". In Randall 's version, it starts with "chord" and "word" which look like they should rhyme, but would be /kɔɹd/ vs. /wɝd/ in an typical US accent. Similarly "shift" and "left" might be considered not a perfect rhyme when read as prose, but should still be possible to meaningfully sing. Technically, a chorded keyboard is one in which (nearly) all inputs are made by simultaneous pressing of a given combination of a limited number of keys, such as a literal handful of non-alphabetic keys, that the user learns to combine to represent the key-presses of more standard keyboards or (in some cases) signify entire phonemes or words. The workings of such a keyboard tends to be handled internally, sending to the computer the signal(s) that would have been sent from its larger cousin. A big thing among Xennial hackers like Randall and his original audience was customising keyboard uses. The linux operating system was originally designed and used for personal customisation, and people move their configurations from system to system, often customising how things respond to such a degree that other users struggle to make use of their system at all. The first major two text editors, vim and emacs, were composed of different camps of how to efficiently type. The emacs camp believed it was more effective to hit many keys at once to accomplish a large task, but both editors were designed to be highly customisable. It's erroneously believed that the traditional qwerty keyboard was specifically designed to make typing inefficient so as to reduce engineering burden in making old typewriters responsive and reliable. Given the prevalence of them, it has been common among hackers to remap a keyboard to something they may personally consider more efficient, such as to use a dvorak layout layout rather than a qwerty layout. Chorded configurations are an order of magnitude more efficient than the dvorak layout, but are more complex to configure because the result is not at all a one-to-one mapping. The traditional court reporting device is a chorded keyboard, to keep up with human speech. Using a combination of normally single-use keys (the 'H' and a cursor) with others, including modifiers ('shift' and 'control'), i.e. 'chording' with his keyboard, is a kind of key combination found traditionally in emacs and operating system commands (such as pressing ctrl+alt+c, to copy a selection to clipboard). The ballad then comes across as an ode to system customisation and the practice of user-interface hacking, wherein a computer user knows how to rebuild their interface in almost any way they desire. The chording example goes beyond mainstream use (shift and an alphabetic character changes the character case, whilst ctrl and a character may initiate an editing command) or mainstream multi-modifier combinations (ctrl, alt and the 'e' may result in the 'é', where the keyboard does not otherwise support it) and even goes beyond emacs-like command sequences which are generally software-specific. It seems likely that a setup such as that depicted in this comic is handled within the computer, either defined within the OS (all mainstream desktop operating systems support alternative keyboard mapping and customisable key-combinations, often for accessibility and international keyboard support), or (as is often the case with specialist configurable gaming keyboards) via the driver installed to mediate such esoteric keyboard combinations as the user has predefined for themselves. Cueball's combination-keypress may in fact be better termed a 'macro', in some contexts. The single event, somehow triggered by this particular simultaneous multi-key input, invokes the injection of a pre-specified sequence of standard characters into the appropriate text-buffer/-stream, in lieu of manual per-character input. The title text spoofs the last verse of the (original) song, with "Hallelujah" being replaced by Cueball trailing off musing about having apparently lost the backup of his keyboard configuration, implying that he ended up in a position where he would want to restore said backup (for instance, having tampered with it to the point he is no longer capable of operating the keyboard efficiently, if at all). Here is the original verse, where the title text spoofs the last three lines: I did my best, it wasn't much I couldn't feel, so I tried to touch I've told the truth, I didn't come to fool ya And even though it all went wrong I'll stand before the lord of song With nothing on my tongue but hallelujah As added irony, while in the original that verse is hopeful, with the singer being thankful for experiencing joy even from a relationship that ultimately failed, contrarily in the alt text Cueball is apparently expressing regret. Or, if taken literally, it could instead imply that God himself is questioning Cueball about his tampering with software, which could fit with the running gag of Cueball's (often self-inflicted) computer problems being hyperbolically atrocious . When one modifies one's keyboard config, it can make the system seem unusable (or at least highly unexpected) to things like a boss, a spouse, or an automated maintenance system. When an error is made somewhere in the process, it can make the system seem unusable to the very person who made the changes, making it hard to change them back. [Cueball is sitting in an office chair at his desk, typing on his keyboard as shown by small lines over one hand, while looking at the screen of his stationary computer. The screen is on a raised platform on his desk. Lyrical text is written upon each scene, presumably what Cueball is typing.] I heard there was a secret chord That David pressed and it typed a word [A closeup on Cueball in a slim panel. We see him from the waist up, with his hands on the keyboard just beneath the panels frame.] But you don't use a chorded keyboard, do you [Same setting as in the first panel, except Cueball's arms have moved and there are movement lines above and below his arms.] It goes like this, <control> and <shift> The other hand hits H and <left> [Slimmer panel but same setting as in the first panel, again the arms have moved a bit, with movement lines above them. The final written word of text is marked as arising directly from the computer.] And all at once it types out Computer: Hallelujah

Headline Words

Headline Words

https://www.xkcd.com/2584

https://www.explainxkcd.com/wiki/index.php/2584:_Headline_Words

[White Hat, Megan, Cueball, and Ponytail stand in a row, with White Hat and Megan facing toward the right and Cueball and Ponytail facing toward the left.] Megan: Maybe Rob shouldn't host the party. He has cats and some of us are allergic. Cueball: Wow, major snub for widely-touted top spot as lavish gala bid nixed. Megan: Why are you talking so weird? Please stop. Cueball: Ill-advised scheme mulled as tension mounts amid growing backlash. [Caption below the panel:] My project to speak only in weird headline words didn't last long.

White Hat , Megan , Cueball and Ponytail are planning a party. Megan mentions that the party was planned to be at Rob's place, but that this might not be a good idea, since he has cats, and some of the participants in the party are allergic to cats. This is a valid reason [1] . Seems likely that Megan is one of those that are allergic. Usually Rob is drawn as Cueball, but it is not necessarily Rob that is present, it could just be a discussion among some of the friends that are supposed to come to the party. Cueball then replies to this in news-commentary fashion, using words and phraseologies that are common in headlines but rare in day-to-day use. This is strange enough to prompt Megan to ask him to stop. He continues though, although the gist of his second line is that he will stop speaking that way. That this is indeed the case and what he is actually trying to do is explained in the comics caption. It states that Cueball's project was to speak in weird headline words. And that the project did not last for long. News headlines are often very dramatic explanations of minor events; so are the things Cueball says here. Furthermore, some newspapers write their headlines in a stylized way which relies heavily on shorter words (such as "nixed" for "rejected"), often uses cliches (such as "tension mounts") and omits 'unnecessary' grammatical padding, a style colloquially known as Headlinese . See below for explanation of his headlines. The title text continues with a final headline statement from Cueball, telling everyone that the project was halted. Probably permanently. Here each of the three headlines will be explained. Several of the words used are listed in the wiki article on Headlinese. Wow, major snub for widely-touted top spot as lavish gala bid nixed. According to the list of words: "snub" means to reject; "tout" can mean to suggest something, for approval; here, a "bid" means an attempt; and "nix" also means to put to an end/not allow to happen. The "top spot" is a venue which has status and popularity, while a "lavish gala" is an expensive/impressive festive celebration, in this case being a party. Translating it step by step to more normal English: Almost literal word replacement: "Wow, a significant rejection for a widely suggested venue, which was looking like it was going to be used. Their attempt to host the party will probably fail now" Trim excess words: "This is a big surprise. We have had a significant rejection for the most widely suggested and popular venue. This means they probably won't host the party." What he probably meant: "Gosh, having heard that, it looks like Rob probably won't host the party after all." Ill-advised scheme mulled as tension mounts amid growing backlash. We can use a similar process, along with the list of words, to translate it step by step to more normal English: Almost literal word replacement: "This idea wasn't well thought-out and I'm now reconsidering it as I feel pressured to stop by your increasingly negative reactions" Apply more context and rearrange: "This idea wasn't well thought-out, and your reactions are making me uneasy, so I should probably stop" What he probably meant: "This was a bad idea and I can tell that you won't tolerate this much longer, so I should probably stop." Roundly-condemned headlinese initiative shuttered indefinitely. (title text) This time the sentence yields to relatively trivial word replacement: "Nobody liked me trying to speak like this, so I'm going to stop forever." What he probably meant: "You all clearly hate me doing this, so I'll stop." [White Hat, Megan, Cueball, and Ponytail stand in a row, with White Hat and Megan facing toward the right and Cueball and Ponytail facing toward the left.] Megan: Maybe Rob shouldn't host the party. He has cats and some of us are allergic. Cueball: Wow, major snub for widely-touted top spot as lavish gala bid nixed. Megan: Why are you talking so weird? Please stop. Cueball: Ill-advised scheme mulled as tension mounts amid growing backlash. [Caption below the panel:] My project to speak only in weird headline words didn't last long.

Rounding

Rounding

https://www.xkcd.com/2585

https://www.explainxkcd.com/wiki/index.php/2585:_Rounding

[In the top left part of the panel is a small drawing where Cueball, wearing a bike helmet and holding a bike, is speaking to Megan.] Cueball: I can ride my bike at 45 MPH. Cueball: If you round. [To their right is a large number with unit, with an arrow going straight down to a normal sized similar number. From there and proceeding all the way down to the bottom, in alternating leftward and rightward rows, the rest of the comic shows arrows connecting conversions from one measured unit into another unit. Straight arrows show the direction of the sequence on each line, the end of each line curveing down to start the next line in the opposite direction. The last of these lines ends close to the middle of the panel, with a straight arrow down to another large number with unit, like the first.] 17 MPH 8 meters/sec 16 knots 5 fathoms/sec 3 furlongs/min 6 fathoms/sec 40 KPH 22 knots 41 KPH 204 furlongs/hr 26 MPH 12 M/S 4 furlongs/min 15 yards/sec 8 fathoms/sec 15 M/S 34 MPH 5 furlongs/min 33 knots 19 yards/sec 10 fathoms/sec 36 knots 6 furlongs/min 45 MPH

This comic is about the follies of unit conversion. Normally, when you say you can ride a bike at 45 mph if you round, you mean that you can ride at a speed between 44.5 and 45.5, something most people are incapable of doing. [ citation needed ] The joke is that Cueball actually means if you go through a extremely long chain of rounding imprecisely (see below ), starting at 17 mph (which is equivalent to 27.4 km/h and not an improbable speed for an ordinary road-bike and a reasonably fit rider), you can get to the value of 45 (72.4 km/h). Randall also esoterically uses some more historic units here: fathoms/sec, furlongs/min, and furlongs/hr. A fathom is a unit of length, in the modern era being equivalent to six feet, usually used to measure the depth of water. Fathoms/sec could potentially be used to measure the ascent/descent speed of a submersible, but it would normally be a strange choice to enumerate the speed of a bike. A furlong is also a unit of length, equivalent to one eighth of a mile (or 660 feet or 110 fathoms) but is mostly unused except in horse racing. It is possible that furlongs/min or furlongs/hour could be used to measure the speed of a horse. Knots (nautical miles per hour) are a standard unit of measuring speed, but are typically used for measuring speed for airplanes or ships, not speed on land. However, km/h (kilometers per hour, spelled kph in the comic) is commonly used internationally to state the speed of land vehicles, while m/s (meters per second) is a measurement encountered in scientific usage. The title text furthers the joke by taking the imprecise rounding literally, implying that this increase could actually be used/abused as a novel form of propulsion, but it isn't clarified for what type of vehicle. It could be an engine for ground or air travel, but contains the implication that it is trying to 'trick physics' similar to the theoretical 'warp drive' conceived to propel interstellar spacecraft at otherwise impossible speeds. One interpretation of the supposed chain of conversions is that it has somehow created a great deal of energy from nothing. Suppose there existed a device or system that could magically accelerate an object from 17 mph to 45 mph without any energy input. The sped-up object could be harnessed to a generator or engine in such a way that the object was slowed back down to 17 mph, with the difference in energy being output in a useful way, and the object fed back into the device. The result would be an engine that could create both free energy and non-conserved changes in momentum. At the demonstrated rate of about 4% medium rounding gain, it would just take 73 more steps of rounding-acceleration to reach supersonic speed from the starting speed of 45 mph. If the speed of light could be approached without relativistic effects, another 349 steps would go from supersonic speed to the speed of light. (More efficient approaches may exist.) [In the top left part of the panel is a small drawing where Cueball, wearing a bike helmet and holding a bike, is speaking to Megan.] Cueball: I can ride my bike at 45 MPH. Cueball: If you round. [To their right is a large number with unit, with an arrow going straight down to a normal sized similar number. From there and proceeding all the way down to the bottom, in alternating leftward and rightward rows, the rest of the comic shows arrows connecting conversions from one measured unit into another unit. Straight arrows show the direction of the sequence on each line, the end of each line curveing down to start the next line in the opposite direction. The last of these lines ends close to the middle of the panel, with a straight arrow down to another large number with unit, like the first.] 17 MPH 8 meters/sec 16 knots 5 fathoms/sec 3 furlongs/min 6 fathoms/sec 40 KPH 22 knots 41 KPH 204 furlongs/hr 26 MPH 12 M/S 4 furlongs/min 15 yards/sec 8 fathoms/sec 15 M/S 34 MPH 5 furlongs/min 33 knots 19 yards/sec 10 fathoms/sec 36 knots 6 furlongs/min 45 MPH

Greek Letters

Greek Letters

https://www.xkcd.com/2586

https://www.explainxkcd.com/wiki/index.php/2586:_Greek_Letters

[A list with 21 explanations of different Greek letters. To the left, the letter (in one case two letters) are shown, and then the explanation is written to the right in one or two lines (and in one case on three lines). Above these explanations, there is a header in a slightly larger font:] What Greek letters mean in equations π This math is either very simple or impossible. Δ Something has changed. δ Something has changed and it's a mathematician's fault. θ Circles! Φ O R B S ϵ Not important, don't worry about it. υ,ν Is that a v or a u? Or...oh no, it's one of those . μ This math is cool but it's not about anything that you will ever see or touch, so whatever. Σ Thank you for purchasing Addition Pro ®! Π ...and the Multiplication ® expansion pack! ζ This math will only lead to more math. β There are just too many coefficients. α Oh boy, now this is math about something real. This is math that could kill someone. Ω Oooh, some mathematician thinks their function is cool and important. ω A lot of work went into these equations and you are going to die here among them. σ Some poor soul is trying to apply this math to real life and it's not working. ξ Either this is terrifying mathematics or there was a hair on the scanned page. γ Zoom pew pew pew [space noises] zoooom! ρ Unfortunately, the test vehicle suffered an unexpected wing separation event. Ξ Greetings! We hope to learn a great deal by exchanging knowledge with your Earth mathematicians. ψ You have entered the domain of King Triton, ruler of the waves.

Mathematics uses lots of Greek letters, typically using the same letter consistently to represent a particular constant or type of variable. This comic gives a (non-)explanation of what they typically mean, see below . In the title text the joke about capital Xi from the main comic is continued. In the main comic those using Ξ (capital xi) greets us as Earth mathematicians, indicating they are not from Earth, but have come here to learn what we know of math. In the title text the idea that any one using Ξ must be aliens is made clear. So if you ever meet someone using this letter while doing math, then learn as much as you can by quietly observing them, before they return to their home planet. Either learn from their possible advanced math (that allowed them to construct a way to get from one star system to another), or learn about them as the aliens species they represent. Previously Randall made a similar comic, 2520: Symbols , about math symbols. [A list with 21 explanations of different Greek letters. To the left, the letter (in one case two letters) are shown, and then the explanation is written to the right in one or two lines (and in one case on three lines). Above these explanations, there is a header in a slightly larger font:] What Greek letters mean in equations π This math is either very simple or impossible. Δ Something has changed. δ Something has changed and it's a mathematician's fault. θ Circles! Φ O R B S ϵ Not important, don't worry about it. υ,ν Is that a v or a u? Or...oh no, it's one of those . μ This math is cool but it's not about anything that you will ever see or touch, so whatever. Σ Thank you for purchasing Addition Pro ®! Π ...and the Multiplication ® expansion pack! ζ This math will only lead to more math. β There are just too many coefficients. α Oh boy, now this is math about something real. This is math that could kill someone. Ω Oooh, some mathematician thinks their function is cool and important. ω A lot of work went into these equations and you are going to die here among them. σ Some poor soul is trying to apply this math to real life and it's not working. ξ Either this is terrifying mathematics or there was a hair on the scanned page. γ Zoom pew pew pew [space noises] zoooom! ρ Unfortunately, the test vehicle suffered an unexpected wing separation event. Ξ Greetings! We hope to learn a great deal by exchanging knowledge with your Earth mathematicians. ψ You have entered the domain of King Triton, ruler of the waves.

For the Sake of Simplicity

For the Sake of Simplicity

https://www.xkcd.com/2587

https://www.explainxkcd.com/wiki/index.php/2587:_For_the_Sake_of_Simplicity

[Cueball is standing beside a table holding his arms out to each side. He has a small object in his right hand. Ponytail and White Hat are sitting on either side of the table. They have a board game between them with several small objects, like the one in Cueball's hand, but with different heights standing on the table. There is also a stack of cards near Ponytail to the left. Both players have their hands on some of the small objects on the table.] Cueball: You may assign each gardener's token to a secondary garden plot within a 30-minute walk from their home plot. Cueball: For the sake of simplicity, each gardener is assumed to have a constant walking speed proportional to their height and cardio score. Cueball: For the sake of simplicity, cardio scores are inherited matrilineally... [Caption below the panel:] If you're worried that you're making something too complicated, just add "for the sake of simplicity" now and then as a reminder that it could always be worse.

Cueball appears to be explaining a gardening-related board game to Ponytail and White Hat . The game mechanics being employed are ridiculously overcomplicated for a game that seems to be about gardening — the cardiovascular health of the gardeners is tracked, for example. However, Cueball uses the refrain "for the sake of simplicity" to imply that the rules could be even more complicated . For example, the walking speed — already a surprisingly complex element — is constant instead of varying based on conditions, and the cardio scores — inherited matrilineally, requiring players to keep track of their gardeners' lineage — at least does not require players to calculate a random combination of many ancestors. It's shown pretty quickly that Cueball's mechanics are needlessly intricate, and his definition of "simplicity" is not nearly simple enough: the lore of the game says gardeners may tend to secondary plots no more than "a 30-minute walk from their home plot", but where most games would simply state an arbitrary number of tiles a gardener token may walk, Cueball expects his players to calculate how far an adult human actually walks in 1800 seconds. This immediately spirals into the game tracking far more variables than necessary such as height and "cardio score", or even things like the curvature of spacetime in the area, and the direct inheritance of a single "cardio score" which requires tracking the gardener's matrilineal line — instead of factors more typical to games such as weather or terrain. Features of Cueball's game include: As gardening is itself an oddly mundane premise for a board game, [ citation needed ] it is entirely possible that gardening is just a minor element of a much broader game. The title text mentions that the space is assumed to be Euclidean , which is what most people would assume since it corresponds to our normal experience, so this is not something that normally needs to be explained. But then it says that this isn't true in the vicinity of a Schwarzschild Orchid. An orchid is a type of flowering plant, which is relevant to a gardening game, but Schwarzschild refers to Karl Schwarzschild , a physicist who solved equations related to general relativity ; the Schwarzschild radius is the boundary of a black hole , and spacetime is severely warped in this vicinity, so Euclidean geometry and Newton's Laws don't describe motion here well. Most boardgames that even care about Euclidean principles only apply them to the 2D planar playing-surface, it seems possible that Cueball has already accounted for the slight (but non-zero) effects of the curvature of the Earth and/or changes in elevation across the apparently detailed simulation within the game environment, through 3D Euclidean space. And, further, the title text implies he actually sat down to calculate the distortion of general relativity upon the walking speed of an adult human, then later used these equations for an entire game mechanic — albeit one that players can mercifully skip when there are no gardeners in proximity of Schwarzschild Orchids. The next comic 2588: Party Quadrants , also mentions complicated rules for scoring a contest. This seems somewhat related to the complicated rules of this game. [Cueball is standing beside a table holding his arms out to each side. He has a small object in his right hand. Ponytail and White Hat are sitting on either side of the table. They have a board game between them with several small objects, like the one in Cueball's hand, but with different heights standing on the table. There is also a stack of cards near Ponytail to the left. Both players have their hands on some of the small objects on the table.] Cueball: You may assign each gardener's token to a secondary garden plot within a 30-minute walk from their home plot. Cueball: For the sake of simplicity, each gardener is assumed to have a constant walking speed proportional to their height and cardio score. Cueball: For the sake of simplicity, cardio scores are inherited matrilineally... [Caption below the panel:] If you're worried that you're making something too complicated, just add "for the sake of simplicity" now and then as a reminder that it could always be worse.

Party Quadrants

Party Quadrants

https://www.xkcd.com/2588

https://www.explainxkcd.com/wiki/index.php/2588:_Party_Quadrants

[A solid black lined square chart is divided into four quadrants with two light gray lines. Above the chart the left and right column are labeled, and above the labels there is a bracket with a label written on the bracket. Similarly there is labels to the left, of the top and bottom rows, with a bracket indicating those also with a label written on the bracket:] Top: Fun for me Top: No Yes Left: Fun for guests Left: No Yes [The top left quadrant is empty. The same goes for the bottom left quadrant, except labels for items in the bottom right quadrant is written in the bottom left quadrant. In the top right quadrant, there is a single black point which is almost touching the right edge of the chart, and lies about a quarter of the way down from the top towards the gray line. The point is labeled:] Label: Sporcle geography tournament Label: with snacks! Label: Live-updating scoreboard, no distracting music [In the bottom right quadrant there is a Venn diagram. It consist of two skewed ellipsoids, one with a solid line overlapping the other with a dotted line. The solid lined region goes further to the left, and the dotted line region goes further to the top, but both are mainly in the bottom right region, and the bottom right section is completely overlapping. Both regions are indicated with an arrow that goes to them from a label. The solid lined regions label is written to the left and it is entirely inside the bottom left quadrant. The dotted lined regions label is written in both of the lower quadrants, thoug mainly above the Venn diagram in the bottom right quadrant.] Solid lined label: Appropriate zone for a party Dotted lined label: Appropriate for my birthday party

In this comic there is a graph divided into quadrants to visualize the range of possibilities of fun for Randall and for guests at parties hosted by Randall. The top and bottom halves are labeled as "fun for guests" with "no" in the top quadrant and "yes" in the bottom quadrant. The left and right halves labeled as "fun for me", i.e. fun for the host Randall, with "no" in the left quadrant and "yes" in the right quadrant. In the bottom right quadrant (which indicates fun for everyone), are two separately outlined but largely overlapping regions, like a Venn diagram . One is the appropriate zone for a party (in general) and the other other applies to Randall's own birthday party. They are both vaguely ellipsoid and both enclose a reasonable to nearly maximal amount of fun in both dimensions. The key difference is that the range of the birthday party is skewed towards being marginally more for Randall's enjoyment, but is still firmly in the bottom right quadrant. By contrast, the range for a party is weighted more towards "Fun for Guests" and less towards "Fun for Me", as befits an event hopefully hosted to entertain its guests and make them feel special. Omitting the extreme edges may indicate that there are no points there because it's impossible to completely please everybody, or it may be a warning that a party should not be such extreme fun that it gets out of hand nor let the balance of fun stray too far from equal. There are no specific points labeled in this quadrant. The joke is that the only data point, presumably Randall's latest idea for a party, is in the upper right quadrant, signifying that it is only fun for Randall! It is very far right and fairly close to the top, indicating extreme fun for Randall and not fun at all for anyone else. The point is labeled "Sporcle geography tournament with snacks! Live-updating scoreboard, no distracting music". The elements of Randall's "fun" party include: In the caption it is mentioned that for some reason, Randall keeps "accidentally" planning parties in the top right quadrant (fun for him, not for guests). Presumably he is so caught up in what he considers entertaining that he doesn't take into account the interest level of the guests. This is regardless of which party-context, and well outside either of the appropriate zones. This diagram though indicates that he know this is the case, but maybe he is first able to place the point on the diagram after the party, when he realizes that his guest leaves early (again) out of boredom. The title text elaborates on the Sporcle trivia game night that Randall has planned in the upper right quadrant. It makes mention of a comprehensive, and perhaps overly complicated, scoring system to determine who is the party's winner. That he's talking about "winning the party" suggests he is fundamentally misunderstanding the point of parties -- they're supposed to be fun for everyone attending, not (exclusively) a competition. See the previous comic 2587: For the Sake of Simplicity , which seems to be a bit related to what Randall thinks is fun, whereas other might not. [A solid black lined square chart is divided into four quadrants with two light gray lines. Above the chart the left and right column are labeled, and above the labels there is a bracket with a label written on the bracket. Similarly there is labels to the left, of the top and bottom rows, with a bracket indicating those also with a label written on the bracket:] Top: Fun for me Top: No Yes Left: Fun for guests Left: No Yes [The top left quadrant is empty. The same goes for the bottom left quadrant, except labels for items in the bottom right quadrant is written in the bottom left quadrant. In the top right quadrant, there is a single black point which is almost touching the right edge of the chart, and lies about a quarter of the way down from the top towards the gray line. The point is labeled:] Label: Sporcle geography tournament Label: with snacks! Label: Live-updating scoreboard, no distracting music [In the bottom right quadrant there is a Venn diagram. It consist of two skewed ellipsoids, one with a solid line overlapping the other with a dotted line. The solid lined region goes further to the left, and the dotted line region goes further to the top, but both are mainly in the bottom right region, and the bottom right section is completely overlapping. Both regions are indicated with an arrow that goes to them from a label. The solid lined regions label is written to the left and it is entirely inside the bottom left quadrant. The dotted lined regions label is written in both of the lower quadrants, thoug mainly above the Venn diagram in the bottom right quadrant.] Solid lined label: Appropriate zone for a party Dotted lined label: Appropriate for my birthday party

Outlet Denier

Outlet Denier

https://www.xkcd.com/2589

https://www.explainxkcd.com/wiki/index.php/2589:_Outlet_Denier

[To the left is a power strip with a rocker switch at the top and five outlets, and a connected wire goes from the top off to the left. To the right is the plug that should go into one of the outlets. A curved wire comes from the right and connects to the end of the connector, which is longer than a normal plug. The prongs are visible underneath where the box ends. But instead of ending there, there is a bar horizontal to the first part, which is longer than the power strip itself. There is a D shaped bar attached to this long bar, centred on the middle of the bar. If it was plugged in, the long bar would cover all the other outlets of the power strip.] [Text above the image:] Cursed Connectors #78 [Text below the image:] The outlet denier

This is the fifth installment in the series of Cursed Connectors and presents Cursed Connectors #78: The Outlet Denier. The outlet denier connector in this comic is the large connector to the right. It has a plug on the downward side that is supposed to go into a power strip or other type of outlet. It has two long bars extending up and down off the plug, as well as a D shape on one side with another, slightly less long bar on the other side of the D, that has the cord connected to it. The purpose of the outlet denier is to block access to as many other ports on a power strip as possible, hence the name. It is designed to work with many different types of power strips, such as the standard one displayed in the comic, as well as ones with the sockets rotated 90 degrees (the long bar extending to the cord) and other types of outlets like the triple outlet on the end of many extension cords and two dimensional power strips that extend a couple of outlets left and right as well as up and down (the D shape on the side). The extreme bars to each side may also prevent plugging the Denier into an outlet close to the floor, forcing the user to use a power strip or similar item for it. There is an example power strip displayed to the left of the outlet denier, used to help explain that the outlet denier is designed to block as many other sockets on a power strip as possible. The power strip is presumably of the type with a rocker switch that can turn the entire power bar off. This power bar has five outlets. Many appliances require transformers or other large components on their power cord. Sometimes these "power bricks" are built around the plug. The comic is making fun of these types of power bricks, as they often block access to other sockets on a power strip or wall outlet. This can be really annoying when you want to plug in many different appliances into a power strip. Other plugs are deliberately designed to block the other half of a duplex outlet, preventing users from plugging anything else in that could overload the circuit. The comic could be depicting an extreme case of a cumbersome connector shape designed to block an entire power strip, as the appliance connected to it uses so much power that a single extra item plugged into the power strip would cause problems. The title text says that the outlet denier has bumps on the underside of the long bar that would match up with the location of the rocker switch no matter which outlet of the strip it is plugged into. It's not clear whether this will turn the power switch off or force it always on. But either way, it gets in the way of the user being able to control the power themselves. If it forces it off, then the Outlet Denier cannot even be used. So to at least assume someone might actually use it, it must force it on. Since there are nothing else that can go into the power strip, it is not that important it it is possible to switch it off though. [To the left is a power strip with a rocker switch at the top and five outlets, and a connected wire goes from the top off to the left. To the right is the plug that should go into one of the outlets. A curved wire comes from the right and connects to the end of the connector, which is longer than a normal plug. The prongs are visible underneath where the box ends. But instead of ending there, there is a bar horizontal to the first part, which is longer than the power strip itself. There is a D shaped bar attached to this long bar, centred on the middle of the bar. If it was plugged in, the long bar would cover all the other outlets of the power strip.] [Text above the image:] Cursed Connectors #78 [Text below the image:] The outlet denier

I Shouldn't Complain

I Shouldn't Complain

https://www.xkcd.com/2590

https://www.explainxkcd.com/wiki/index.php/2590:_I_Shouldn%27t_Complain

[Cueball and Megan are standing together. Cueball has his hands on his chin, shocked.] Cueball: I can't believe you fell headfirst into a garbage can and were stuck there for two hours while wasps stung your exposed legs! Megan: I shouldn't complain! Lots of people have been stuck for longer in worse places. Megan: Really, I'm lucky. [Caption below the panel:] The more unpleasant someone's experience is, the more they apologize for complaining because it could be worse.

Humans have a tendency to re-calibrate their mental scales to place their actual experience in the center. Cueball, who has never experienced being trapped for hours with stinging insects, rates this in comparison to not being trapped at all. Megan, however, rates it in comparison to other uncomfortable places a person could be stuck. The title text explains how Megan came into such a mess. A tennis ball used in a clothes dryer got stuck in the exhaust vent, and was shot out of the house through the exhaust vents hole in the wall. Then it hit the wasp nest and ricocheted over on Megan knocking her off the ladder she was standing on. Since she was close to the nest, she may actually have been up on the ladder in order to see if she could remove the nest. The fall from the ladder made her end up in the trash can where she could not get out. The angry wasps began stinging her legs. This continued for two hours. In the title text, Megan continues to downplay her experience even though it was very painful. She says that the wasp nest was of the type bald-faced hornets . The Schmidt sting pain index is a scale developed by entomologist Justin O. Schmidt to rank the relative pain caused by different stinging insects. This scale ranges from 0 (for stings that are completely ineffective) to 4, which denotes torturous and nearly incapacitating pain (originally, Schmidt only classed one species as a 4, but two additional species have since been added at this level). Megan says her stings were a 2 on the scale , which denotes "familiar" pain, comparable to that of the common Western Honey Bee . Most people would find that experience incredibly painful, particularly since she endured multiple stings over a long period of time, but Megan points out that there exist insects with more painful stings. Megan concludes that she'd been lucky, based on the argument that she theoretically could have endured something worse than she did. The joke, of course, is that by almost any subjective standard, her experience was deeply unluckly. She also further downplays the situation by focusing attention on the sting pain index instead of the sting lethal capacity, described by the author of the pain index . The two are not necessarily equivalent. Let's assume that all insects in the colony affected stung Megan at least once over her two hour ordeal. A colony capable of sustaining an attack over two hours would probably be at least as large as the typical maximum size for a bald-faced hornet nest . Such an attack might (depending on number of attackers and the species of wasp) deliver enough venom to kill 84 kg (185 pounds) worth of mice (or human?). Given such an attack, Megan would probably not be standing around in routine conversation, casually discussing the incident. She would far more likely be in a hospital bed, and in a gruesome fight for her life . [Cueball and Megan are standing together. Cueball has his hands on his chin, shocked.] Cueball: I can't believe you fell headfirst into a garbage can and were stuck there for two hours while wasps stung your exposed legs! Megan: I shouldn't complain! Lots of people have been stuck for longer in worse places. Megan: Really, I'm lucky. [Caption below the panel:] The more unpleasant someone's experience is, the more they apologize for complaining because it could be worse.

Qua

Qua

https://www.xkcd.com/2591

https://www.explainxkcd.com/wiki/index.php/2591:_Qua

[Cueball and Megan are speaking to each other.] Cueball: People mostly use "qua" to sound pretentious. You rarely hear qua qua qua. Megan: Nice use of qua qua qua qua qua qua qua.

Saying something is "X qua X" (e.g. "entertainment qua entertainment") means when X is being viewed in its most typical capacity (eg, entertainment as something that entertains, rather than as a business, a form of propaganda, or whatever). For example, "A copy, qua copy, can never be the equal of the exemplar, and it may be much its inferior." [1] Cueball claims that people only use qua to "sound pretentious" without properly understanding its meaning. Thus, people do not use "qua qua qua", or "qua for the sake of qua". However, Megan one-ups this with a series of seven qua s: she compliments Cueball's successful use of "qua qua qua qua qua qua qua", or "the phrase 'qua qua qua' for its correct meaning". The joke is that, for the reader, the conversation has likely dissolved into gibberish because of unfamiliar terminology and semantic satiation . This is similar to other complex sentences such as "Buffalo buffalo Buffalo buffalo buffalo buffalo Buffalo buffalo" , "That that is is that that is not is not is that it it is" , and "James while John had had had had had had had had had had had a better effect on the teacher" . Following this trend, you can create a grammatically correct sentence that includes 'qua' a consecutive number of times equal to (2 n -1), where n is a natural number. The title text goes further with this, using a Latin phrase sine qua non (meaning literally "without which not"), commonly rendered as "that which is absolutely necessary" or "essential". Thus, the title text says that "the word 'qua' in its real meaning is essential to the phrase 'sine qua non' used correctly". However, the **qua** in title text phrase is a demonstrative pronoun ("which"), unlike the other **qua** which is an adverb, so the similarity is only coincidental. [Cueball and Megan are speaking to each other.] Cueball: People mostly use "qua" to sound pretentious. You rarely hear qua qua qua. Megan: Nice use of qua qua qua qua qua qua qua.

False Dichotomy

False Dichotomy

https://www.xkcd.com/2592

https://www.explainxkcd.com/wiki/index.php/2592:_False_Dichotomy

[White Hat and Cueball are talking to each other. White Hat has his arms spread outwards in exasperation, while Cueball gestures assertively with his pointer finger.] White Hat: That's a false dichotomy! Cueball: Yes, but we have to embrace false dichotomies, because the only alternative is cannibalism.

A dichotomy is two alternatives which are normally mutually exclusive (such as the dichotomy between a flat Earth and non-flat Earth). A false dichotomy is a logical fallacy based on an incorrect perception of limited options (for example: if the page background isn't white, it is black). Cueball has apparently made one such error and is being called out by White Hat for it. Upon having this pointed out to him, Cueball says that we must embrace false dichotomies, because the only other option is cannibalism . This statement is another false dichotomy, as presenting false dichotomies is not the only alternative to cannibalism [ citation needed ] . The reverse (that cannibalism is incompatible with expressing false dichotomies) is also not potentially true, as eating people may eventually result in having nobody you need to present false dichotomies to. Cueball has thus created another false dichotomy to excuse his first. The false dichotomy Cueball appears to be referring to is the notion that those identified as human must not be eaten, but even closely related animals are not human and can be eaten, i.e. species can be divided clearly between "human" and "food". If this dichotomy is not accepted, then consuming any species that shares, for instance, any significant percentage of DNA with humans could be considered a measure of cannibalism. The title text states that there are two kinds of dichotomies, making a dichotomy in itself. Due to three types of dichotomy being mentioned, and only two being foreshadowed, this statement is itself a surprise trichotomy, or three-parted choice. The title text is a variation of the "Two kinds of People" joke. The classic math nerd variant is "There are three kinds of people in the world, those who can count, and those who can't." Alternatively, it may refer to a variation about binary . The original joke usually goes something like this: "There are 10 types of people: those who know binary, and those who don't." The variation is usually something like the following: "There are 10 types of people: those who know binary, and those who don't, and those who weren't expecting a ternary joke." Another version of this kind of joke is "there are two kinds of people: those who can extrapolate from an incomplete data set," The word trichotomy is a relative neologism, to be understood as to mean "divided into (or amongst) three parts", having replaced the original prefix "di-" (a factor of two, either doubled or, by context, halved) with that of "tri-" (similarly tripled/thirded). Strictly, though, dichotomy more directly stems from Greek elements that say "apart, I cut", with "apart" being represented by the "dicho-" (itself being roughly "into two", or to separate) which does not have a direct "tricho-" equivalent, although it does ultimately derive from "duo", Greek for "two". This is the kind of linguistic nuance that Randall clearly enjoys, yet may also happily or carelessly (mis)use without compunction. [White Hat and Cueball are talking to each other. White Hat has his arms spread outwards in exasperation, while Cueball gestures assertively with his pointer finger.] White Hat: That's a false dichotomy! Cueball: Yes, but we have to embrace false dichotomies, because the only alternative is cannibalism.

Deviled Eggs

Deviled Eggs

https://www.xkcd.com/2593

https://www.explainxkcd.com/wiki/index.php/2593:_Deviled_Eggs

[The comic consists of four variations of deviled eggs.] [A typical deviled egg, with half of the white part of a hard-boiled egg and a paste of yolk in a rough cone. The paste is speckled with red dots.] Chef Deviled egg [A deviled egg, except the paste has been flattened to be level with the white.] Landscaper Leveled egg [A deviled egg, except the edge of the white has bevels.] Designer Beveled egg [A deviled egg, except the paste is now two hemispheres, one set in (and level with) the white and the other on top with a toothpick wedged between the two hemispheres at the left egg keeping them separated. The toothpick has a small piece of blue foil wrapped around the edge of the toothpick.] Physicist Demon egg

A deviled egg is a dish created by cutting a hard-boiled egg into halves and replacing the yolk with a paste frequently made using the yolk itself, additional ingredients such as mustard and mayonaise , and topped with a red spice (usually paprika ). Importantly, the paste has a larger volume than the original yolk because of the added ingredients (and probably some air) into the originally homogeneous yolk substances. Randall Munroe parodies the dish by creating several alternative versions of the dish for other professions using word plays on the name of the dish. Chef - Deviled egg The original dish with the excess paste piled above the egg white. Landscaper - Leveled egg Many landscaping projects involve leveling irregular ground surfaces. [ citation needed ] A landscaper may prefer to serve their deviled egg with a leveled flat surface. (This happens to resemble a normal hard-boiled egg cut in half.) Designer - Beveled egg Bevels are a design pattern of creating non-perpendicular surfaces between adjacent edges. A designer may prefer to serve their egg with the edge of the white beveled to give their eggs a more modern, aesthetically pleasing look. Physicist - Demon egg This deviled egg is designed to look like the Demon Core which was a sub-critical plutonium sphere manufactured during the Manhattan Project to investigate the properties of criticality . The Demon Core consisted of three parts: two plutonium-gallium hemispheres and a ring designed to keep neutron flux from "jetting" out of the joined surface between the hemispheres during implosion. The set of plutonium pieces got their name from the 2 criticality incidents that occurred when scientists were investigating this property. The first accident resulted in the death of Harry Daghlian . In the second incident, experimenters covered the core with two neutron reflecting shells separated only by a handheld screwdriver. (No, really.) The screwdriver slipped, causing the core to become completely covered by the neutron reflecting shell, bringing the core past its criticality limit. A large amount of radiation caused the subsequent death of physicist Louis Slotin . The dome of the boiled egg and the toothpick resemble the configuration of the experiment. The demon core was also referred to in 1242: Scary Names . The title texts refers to ionized-air glow , a blue light emitted by air submitted to an energy flux from radiation and seen during the incidents involving the demon core . For a detailed explanation of the Demon Core, Kyle Hill produced an Youtube Documentary regarding the Demon Core. [The comic consists of four variations of deviled eggs.] [A typical deviled egg, with half of the white part of a hard-boiled egg and a paste of yolk in a rough cone. The paste is speckled with red dots.] Chef Deviled egg [A deviled egg, except the paste has been flattened to be level with the white.] Landscaper Leveled egg [A deviled egg, except the edge of the white has bevels.] Designer Beveled egg [A deviled egg, except the paste is now two hemispheres, one set in (and level with) the white and the other on top with a toothpick wedged between the two hemispheres at the left egg keeping them separated. The toothpick has a small piece of blue foil wrapped around the edge of the toothpick.] Physicist Demon egg

Consensus Time

Consensus Time

https://www.xkcd.com/2594

https://www.explainxkcd.com/wiki/index.php/2594:_Consensus_Time

Proposal: Consensus Time Every day, anyone in the time zone can press a button when they feel like it's 9 AM. The next day, clocks slow down or speed up to match the median choice from the previous day. [A diagram representing the hours of two days with tick marks, with some of the tick marks longer than others and/or in boldface, and some of them labeled as follows:] Midnight 6AM 9AM today Median Noon 6PM Midnight 6AM 9AM tomorrow Noon 6PM Midnight [A brace connects the period from the second "Midnight" to "9AM tomorrow". It is labeled:] Longer hours [A scatterplot of 57 dots appears below the hashmarks, indicating the distribution of when participants pushed the "9 AM" button. The most extreme outliers are at roughly 3AM and 9PM, but they most densely cluster around a vertical dotted line labelled "Median" at approximately 11:15AM, interrupted as it passes through the main mass of dots at roughly the position of the 29th plotted dot from either end.] [Megan, facing to the left, and Cueball, facing to the right, each hold a handheld device. The devices are too small to see clearly but are making sounds, implying that each of them has just pressed the "9 AM" button.] Beep Beep A working version has been created.

Randall , jumping on this topic, proposes a system that allows everybody to say when it "feels" like 9 am, and then the median 9 am will become the real 9 am. This happens every day. As the title text points out, this would be chaotic and, to put it bluntly, awful. [ citation needed ] Presumably the times indicated on this diagram are as the clocks in this time zone would indicate, as opposed to an "ordinary" reference time. The graph of points seems to follow a normal distribution, with a large number of votes being clustered around a given time, and giving a median of soon after 11AM. There are some extreme outliers, some before 6AM and some after 6PM, indicating some users being outside the normal range but no information on whether it's a malicious attempt. Although the hours between midnight and 9 am are labelled as "longer" (which we can assume means each would take longer than an hour of ordinary time to pass) the effect on the remaining hours is left unstated. If we assume that the remaining hours pass at the usual rate then this would suggest that midnight would come sooner or later than normal and hence the next vote would occur sooner or later respectively. This implies the time in this time zone could drift further than a day (or even multiple days) from existing time-zones which could be what is meant by "feedback", "chaos" and the effect on weekdays mentioned in the title text. Proposal: Consensus Time Every day, anyone in the time zone can press a button when they feel like it's 9 AM. The next day, clocks slow down or speed up to match the median choice from the previous day. [A diagram representing the hours of two days with tick marks, with some of the tick marks longer than others and/or in boldface, and some of them labeled as follows:] Midnight 6AM 9AM today Median Noon 6PM Midnight 6AM 9AM tomorrow Noon 6PM Midnight [A brace connects the period from the second "Midnight" to "9AM tomorrow". It is labeled:] Longer hours [A scatterplot of 57 dots appears below the hashmarks, indicating the distribution of when participants pushed the "9 AM" button. The most extreme outliers are at roughly 3AM and 9PM, but they most densely cluster around a vertical dotted line labelled "Median" at approximately 11:15AM, interrupted as it passes through the main mass of dots at roughly the position of the 29th plotted dot from either end.] [Megan, facing to the left, and Cueball, facing to the right, each hold a handheld device. The devices are too small to see clearly but are making sounds, implying that each of them has just pressed the "9 AM" button.] Beep Beep A working version has been created.

Advanced Techniques

Advanced Techniques

https://www.xkcd.com/2595

https://www.explainxkcd.com/wiki/index.php/2595:_Advanced_Techniques

[Miss Lenhart is using a stick to point at a whiteboard behind her while facing, presumably, a crowd of off-panel students. The white board has a drawing of a snake-shaped dragon with wings, flying with it's body in an S-shape. An archer is pointing an arrow up at the dragon above him. Above the drawings there are three and below two rows of unreadable text and equations.] Miss Lenhart: To solve this equation, we invoke Gauss's operator to transform it into a dragon. Miss Lenhart: Then we slay the dragon with Hilbert's Arrow, and transform its corpse back into the solution. Off-panel voice: Just to be clear, this is a metaphor, right? Miss Lenhart: Does this look like English class?! [Caption below the panel:] All advanced math techniques

In typical Miss Lenhart fashion, she is teaching a mathematics class where she outlines a process by which a mathematical result is achieved through steps which sound suspiciously like magical RPG logic. She includes both a dragon and arrows to slay it. One of her students asks if this is a metaphor for the technique, but her rather tetchy reply "Does this look like English class?!" seems to imply that she literally means that dragons and arrows will be employed in the resolution of the problem. It is also clear from the slide she is pointing at that she has drawn a dragon and a man with a bow that is aiming an arrow at the dragon. Whilst metaphor is an important part of many languages, and so is definitely taught in language classes, it is not usually used in math classes. The caption beneath the comic states that this approach describes "All advanced math techniques." This could be a reference to the now-common approach in higher mathematics in which a problem is transformed into another domain where it is easier to solve, then transformed back. For instance, in Fourier analysis , commonly used for analyzing the behavior of signals or dynamical systems, a problem can be transformed from the time domain to the frequency domain, solved, and then transformed back again. A (much) more complex example is Andrew Wiles's proof of Fermat's Last Theorem , which uses modularity lifting to transform the problem. Here Miss Lenhart says she will transform a math problem into an actual dragon, slay it, and transform the corpse back into mathematics. An alternative view is that Randall is referring to Arthur C. Clarke 's third law that Any sufficiently advanced technology is indistinguishable from magic , as re-framed for mathematics. What Randall would be implying is that all advanced math techniques look like magic to non-mathematicians. (Another advanced and somewhat magical math technique is deployed by Miss Lenhart in 1724: Proofs .) Invocations are a common classification for spoken or vocalized types of spell. In the logic Miss Lenhart used, 'invoking' Gauss's operator may refer to casting a magical spell with verbal components (such as True Polymorph ). The operator is presumably named after the famous German mathematician Carl Friedrich Gauss . There is nothing on Wikipedia called Gauss's operator, but there is both Gauss's law and the Gauss–Kuzmin–Wirsing operator . As neither can transform an equation into a dragon, [ citation needed ] it's clear Randall is making a joke. Slaying the dragon with Hilbert's arrow indicates that the arrow has some magical properties. The arrow is presumably named after David Hilbert , known for many mathematical developments including Hilbert's problems and Hilbert spaces . A Hilbert space converts subsets of an infinite vector space into a complete metric space, allowing the use of linear algebra and calculus methods which might otherwise be applicable only to finite Euclidean spaces. Vectors could be compared with an arrow. Magical arrows are frequently used to slay dragons in myth and role-playing games. Magical items in RPGs such as Dungeons & Dragons are often named after a creator or famous user; hence, a magical "Arrow of Hilbert" might traverse infinite spaces or affect targets for which one or more stats are effectively infinite. There is in fact a class of Dragon curves , which do have the sort of S-shape shown on the whiteboard, but they have no connection to Gauss's operator, and are not actual dragons that need slaying. The title text contains two puns and a reference. The phrase " Cutlass of Variations" is a pun on the mathematical technique called " Calculus of variations ". The word "Noetherworld" is a pun on " netherworld ". The reference is to the mathematician Emmy Noether , a giant in the field of abstract algebra which, through more of Ms. Lenhart’s questionable transformations, may become an actual giant in a field of abstract algae bras. Furthermore, Noether's Theorem is used in the Calculus of Variations. She was previously referenced as one of many important women in science back in 896: Marie Curie . [Miss Lenhart is using a stick to point at a whiteboard behind her while facing, presumably, a crowd of off-panel students. The white board has a drawing of a snake-shaped dragon with wings, flying with it's body in an S-shape. An archer is pointing an arrow up at the dragon above him. Above the drawings there are three and below two rows of unreadable text and equations.] Miss Lenhart: To solve this equation, we invoke Gauss's operator to transform it into a dragon. Miss Lenhart: Then we slay the dragon with Hilbert's Arrow, and transform its corpse back into the solution. Off-panel voice: Just to be clear, this is a metaphor, right? Miss Lenhart: Does this look like English class?! [Caption below the panel:] All advanced math techniques

Galaxies

Galaxies

https://www.xkcd.com/2596

https://www.explainxkcd.com/wiki/index.php/2596:_Galaxies

[An almost white panel with a caption at the top. Then a small circle, much smaller than for instance the letter O in the text is in the center of the panel. A bending arrow points to the circle and beneath the arrow is a caption.] Open this picture fullscreen on your phone and hold it at arm's length. There are 50,000 galaxies in this circle. [Caption below the panel:] Astronomy Fact: There are too many galaxies.

This is another comic with a Fact , the second in a row of these fact comics to use an Astronomy fact. Our best approximation of the number of galaxies in the observable universe is about 200 billion (2 × 10 11 ). That's a lot of galaxies, [ citation needed ] and here Randall exemplifies this by showing a small circle and estimating that when the comic's picture is viewed at a typical arm's length, expanded to full screen on your typical smartphone, the circle contains roughly 50,000 galaxies (that means of course not the small circle itself, but the volume defined by the viewer's eye, that circle, and an onward conical extension into deep space — and simultaneously back in time — to the respective limits of the observable universe). Most of those far-away galaxies are undetectable by even our most powerful astronomical instruments today, and comparatively few could be seen (let alone positively identified as such) by the naked eye. For example, in the Hubble Deep Field , an image of a small region in the constellation Ursa Major, about 3,000 visible galaxies can be identified. Measuring in the mid-point of the lines, the circle is about one fortieth of the width of the frame of the comic. The absolute circle size depends on the display resolution, size and mode, but it can reasonably be taken to be 1mm diameter, or 0.5mm radius, giving a total area π r 2 or about π/4 square millimeters. You're probably holding the phone about a half a meter away from your eye. The surface area of a sphere is 4 π r 2 . With a radius of one-half meter, that comes out to be π square meters. Thus, the area of the circle is about 1/4000000 of the area of the sphere, 200 billion galaxies divided by 4 million is the 50,000 average mentioned in the cartoon. A similar mathematics was used for the comic 1276: Angular Size , in which the projective sphere was at the Earth's own radius and cross-sectional areas of objects were compared, rather than an approximate count of objects within a given angular spread. While galaxies usually are between 3,000 to 300,000 light-years across and contain between 10^8 (100 million) and 10^14 (100 trillion) stars, most are so far away from the Earth (upwards of billions of light-years) that they are invisible to the naked eye, or even through most telescopes. When magnified across such vast distances, even something as small as a pinhole expands to huge sizes, easily able to fit tens of thousands of galaxies. The premise of this comic is that although galaxies are giant, space is unimaginably big and contains a vast number of things. Randall is apparently overwhelmed by this, as shown in the caption: Astronomy Fact: There are too many galaxies . The title text is Randall reassuring his readers why not to worry of this overwhelming fact. He states that most galaxies only have few stars and probably no planets. However, as mentioned above each galaxy contains a huge amount of stars, and as evident from all his own comics about exoplanets , it is now clear that many of the stars in a galaxy also have planets orbiting them. Thus the number of stars and planets in that small circle is much more mind-bogglingly large, than the number of galaxies, and thus the reassurance is sarcasm. In 975: Occulting Telescope Cueball expresses a similar sentiment about the number of stars. [An almost white panel with a caption at the top. Then a small circle, much smaller than for instance the letter O in the text is in the center of the panel. A bending arrow points to the circle and beneath the arrow is a caption.] Open this picture fullscreen on your phone and hold it at arm's length. There are 50,000 galaxies in this circle. [Caption below the panel:] Astronomy Fact: There are too many galaxies.

Salary Negotiation

Salary Negotiation

https://www.xkcd.com/2597

https://www.explainxkcd.com/wiki/index.php/2597:_Salary_Negotiation

[Ponytail sits in an office chair at her desk, with Cueball sitting in a similar chair on the other side with his hands on his knees. Ponytails has her hands on the desk and in front of her, there is a slim thing standing up. It could be a very small screen, but there seems to be no keyboard in front of her. Maybe it is a small tablet with a support for letting is stand up. Behind that there are what appears to be two piles of papers of different sizes.] Ponytail: We'd like to extend an offer! The starting salary is $55,000. Cueball: Wow. I guess I'm inside a negotiation! Ponytail: I... Weird to phrase it like that, but- Cueball: I can do this. [Zoom in on Cueball's upper half.] Cueball: I won't accept a penny over $50,000. Sorry, I mean under. Under $60. I mean, $600. Thousand. $600,000. I want a 15% cut of the salary. Raise. Double down. Fold. Pass. Fill it up with regular. [The same shot, except Cueball is now holding three pieces of paper, and he is looking down on them. Ponytail is talking to him from off-panel.] Ponytail (off-panel): Are you- Cueball: Sorry, sorry. Let me start over. Cueball: OK, my chart says... Cueball: ...Can I borrow a calculator? What's 20% of $55,000? [Back to the scene from the first panel. Ponytail has taken one hand down to her knee, with the other still on the desk. Cueball has put the papers on his lap and has raised his hand in the air holding one finger up. In his other hand he holds either a borrowed calculator or his own smartphone.] Ponytail: Listen, if you need to- Cueball: I won't take this job for less than $61,333 point 3 repeating! Ponytail: Sure, $61,333 is fine. That's actually- Cueball: Point 3 repeating or I walk!

Ponytail 's company would like to hire Cueball for a job, and she is telling him that their offer for his starting salary is $55,000. When offered a new job, it is common to negotiate on aspects of the offer such as salary, and employers may offer below the market rate initially in the expectation that the final negotiated amount will be higher. Given that the bedrock of one's future income depends on the outcome of a one-time process requiring skills unrelated to the job one is hired for, it is advisable to take one's time and do as much research as possible. Cueball has clearly done some research, but perhaps too much as he is flummoxed by this high-stakes situation and starts to ramble with decreasing coherence. First he gets completely confused about the numbers. He says he won't have a penny over $50,000, thus cutting $5000 of the initial offer, and saying he will not have more than that. He realizes this was completely wrong, and corrects to "under", but is still 5000 lower. He then fumbles his words, asking for $60, then $600, then adding "thousand" for $600,000. Realizing that he is completely off, he asks for a "15% cut of the salary". Here, Cueball seems to confuse salary and commission. "X% cut of the salary" seems like what a recruiter/headhunter may get from their employer as a commission if they successfully make their person hired. The next word he says is "Raise". This could make sense if he already had a job, and wished to negotiate for a pay raise. After this, he begins to think of raise as in a card game and starts rambling off mainly poker related terms, like "raise", "fold" and "pass". He throws in "double down" in between. This can also be a card game term, as in blackjack where double down means to double a bet after seeing one's initial cards, with the requirement that one additional card be drawn. Lastly, he randomly mentions "fill it up with regular", which could be a request to a gas station attendant to fill a vehicle with "regular" (compared to higher octane) gasoline. Ponytail tries to ask him something, but Cueball interrupts her, saying he is sorry and that he would like to start over. At this time he takes out several sheets of paper and looks at some charts. He asks if he can borrow a calculator and then asks what's 20% of $55,000. (This would be $11,000.) He eventually settles on a number, $61,333. 3 He even states that the decimals of 3 should be repeating, as in forever. This is exactly $61,333⅓. He clearly states he will not take the job for less than that. A 2016 Harvard Business School study found that avoiding round numbers is a remarkably effective negotiation tactic. Since this is not that much more than the starting offer Ponytail is ready to accept this and says "Sure, $61,333 is fine." But Cueball interrupts her because what she just offered him was 33⅓ cents less than he asked for. In the title text it shows that this is not good enough. Cueball has now confused himself to the point he will only accept exactly what he asked for, the bizarre amount $61,333⅓. Ponytail tries to explain to him that the point 3 repeating cannot be paid in whole cents, and tries to let him know that their payroll software only can handle whole cents, and he thus can get either 0.33 or 0.34 (the latter actually being more than he asks for). Alas, Cueball, either out of panic or a love of mathematics, shouts "No deal!" and lets the job slip out of his hands, because he has completely misunderstood the concept of negotiation. For more interview-related xkcd comics, see for instance Category:Job interviews . This could also be taken in series with Cueball (possibly as a stand in for Randall) misunderstanding classically "adult" ideas, see for instance 616: Lease , 905: Homeownership , 1674: Adult and 1894: Real Estate . [Ponytail sits in an office chair at her desk, with Cueball sitting in a similar chair on the other side with his hands on his knees. Ponytails has her hands on the desk and in front of her, there is a slim thing standing up. It could be a very small screen, but there seems to be no keyboard in front of her. Maybe it is a small tablet with a support for letting is stand up. Behind that there are what appears to be two piles of papers of different sizes.] Ponytail: We'd like to extend an offer! The starting salary is $55,000. Cueball: Wow. I guess I'm inside a negotiation! Ponytail: I... Weird to phrase it like that, but- Cueball: I can do this. [Zoom in on Cueball's upper half.] Cueball: I won't accept a penny over $50,000. Sorry, I mean under. Under $60. I mean, $600. Thousand. $600,000. I want a 15% cut of the salary. Raise. Double down. Fold. Pass. Fill it up with regular. [The same shot, except Cueball is now holding three pieces of paper, and he is looking down on them. Ponytail is talking to him from off-panel.] Ponytail (off-panel): Are you- Cueball: Sorry, sorry. Let me start over. Cueball: OK, my chart says... Cueball: ...Can I borrow a calculator? What's 20% of $55,000? [Back to the scene from the first panel. Ponytail has taken one hand down to her knee, with the other still on the desk. Cueball has put the papers on his lap and has raised his hand in the air holding one finger up. In his other hand he holds either a borrowed calculator or his own smartphone.] Ponytail: Listen, if you need to- Cueball: I won't take this job for less than $61,333 point 3 repeating! Ponytail: Sure, $61,333 is fine. That's actually- Cueball: Point 3 repeating or I walk!

Graphic Designers

Graphic Designers

https://www.xkcd.com/2598

https://www.explainxkcd.com/wiki/index.php/2598:_Graphic_Designers

[Cueball stands in a lightly adorned room of a house, facing an open doorway. Each surface is painted an almost imperceptibly different shade of off-white, except the floor which is white. There is a rug, a couch with a pillow (white) and a book. There are two windows, in the right there is a potted plant. Knit Cap stands in the open doorway, as if about to enter the house, one foot at the threshold, but not on the floor inside. Cueball is reaching towards the doorway, inviting Knit Cap to enter.] Cueball: Come on in! We just repainted. Knit Cap: I... can't. [Caption below the panel:] If you want to set up a vampire-style barrier to keep graphic designers from entering your house, just paint every surface a slightly different shade of off-white.

Being presented with visual information that is just not quite right is known to cause feelings of unease and revulsion, particularly when presented with CGI human faces, a concept known as the uncanny valley . In the title text, it mentions a contingency against the designer managing to actually overcome this disgust. In this case, Cueball sets up a second way to troll his graphic designer friend using some picture frames, a level , and a protractor that can measure increments of less than a degree. Cueball can then skew his picture frames by an extremely small amount, noticeable only to the designer friend, to disgust him even further — similar to the effect of bad kerning . This could thus be applied like the use of crosses or garlic , which vampires are famously repulsed by. Although the window ledges are slightly inclined, falling subtly from left to right, it is unlikely this is a deliberate aspect of the room so much as a side-effect of Randall's imprecise stick-figure drawing style. True to the comic's joke, Randall has actually colored each segment of the comic differently to each other, even though normal persons would just perceive all walls as slightly gray (off-white). The hexadecimal color codes are: Whilst this subtle difference may be undetectable to humans without a graphic design qualification, it can be made clearer by increasing the saturation value of the image, as shown in this rendering with an exaggerated color saturation . [Cueball stands in a lightly adorned room of a house, facing an open doorway. Each surface is painted an almost imperceptibly different shade of off-white, except the floor which is white. There is a rug, a couch with a pillow (white) and a book. There are two windows, in the right there is a potted plant. Knit Cap stands in the open doorway, as if about to enter the house, one foot at the threshold, but not on the floor inside. Cueball is reaching towards the doorway, inviting Knit Cap to enter.] Cueball: Come on in! We just repainted. Knit Cap: I... can't. [Caption below the panel:] If you want to set up a vampire-style barrier to keep graphic designers from entering your house, just paint every surface a slightly different shade of off-white.

Spacecraft Debris Odds Ratio

Spacecraft Debris Odds Ratio

https://www.xkcd.com/2599

https://www.explainxkcd.com/wiki/index.php/2599:_Spacecraft_Debris_Odds_Ratio

[A chart is shown. Above the chart there is a heading, with a subheading below it:] Odds ratio for head injuries from falling spacecraft debris (Monte Carlo Simulation) [The chart is rectangular with the X-axis labels above the chart with numbers from 1 to 5. These are places over vertical lines. The first at 1 is black, the other four are light gray. There are three smaller light gray ticks between each set of lines, and one on either side of the first and last. The distance between lines gets smaller and smaller towards the right, probably logarithmic.] X-axis: 1 2 3 4 5 [The Y-axis is not scaled; there are no ticks or lines. Instead it just gives five labels from top to bottom. Above those labels there is an arrow pointing to the top one with a label above explaning the axis.] Hours spent outdoors per day Y-axis: 0 (ref) 1 2-4 5-10 11+ [Aligned with each of these five divisions of the Y-axis there is a dot. The top one is placed on the solid line under 1 as a reference point. The other four dots all have long error bars, with the dots at the center of these. The second dot is a bit to the left of the solid line, with the error bar going almost to the left edge of the graph and halfway to the first light gray line to the right. The third dot is located halfway between the solid and the first light gray line with the error bar just crossing the solid line, and almost reaching the gray line. The fourth dot is about a third way between the first and second of the gray lines, with the error bar crossing both these lines. The fifth and last dot is just past the second gray line, with the error bar crossing both that, going more than half toward the first gray line, and also just past the third gray line. On the same height as the two bottom dots, there are asterisks just right of the edge of the graph.] * * [Below the panel there is a caption:] Our new study suggests that spending more than 5 hours outside significantly increases your risk of head injury from spacecraft debris, so try to limit outdoor activities to 4 hours or less.

This comic is a misunderstanding of statistics very similar to that of 1252: Increased Risk . It explains that going outside for more than 5 hours per day significantly increases your risk of head injury from falling spacecraft, and advises to limit outside activity to avoid this risk. However, since the odds of being hit in the head by (any part of) a falling spacecraft are astronomically low to begin with , quadrupling it or more still results in a negligible probability. The horizontal error bars for times greater than 4 hours are marked with asterisks to indicate they are significantly different from the reference value at 0 hours, as indeed those error bars don't overlap the vertical line for the 0-hours reference value. Error bars are graphical representations of the variability of data and used on graphs to indicate the error or uncertainty in a reported measurement. Presenting the data by hour brackets hides the data distribution inside each bracket. If the data were presented hour by hour, and not by groups of hours, they may show a different threshold of increased risk or no threshold (odds ratio could be linear). The graph and error bars are based on a Monte Carlo simulation , a type of computational algorithm that uses repeated random sampling to obtain the likelihood of a range of results of occurring; see, for instance, this article about Monte Carlo simulations . Additionally, this may indicate that the entire study was conducted via a Monte Carlo simulation and that no real data was collected adding to the absurdity of the claim that more time spent outside could lead to an increased risk of head injuries due to falling space craft. Indeed, it is so rare for humans to be struck by spacecraft debris that a simulation is probably the only way to study the risk; an absurdly large sample size, involving tens of millions of participants over several decades, would be necessary to obtain significant experimental data. The specific reference to falling spacecraft is likely inspired by events happening around the time of this comics release (March 2022). Around a month before this was posted, the head of the Russian space agency, Roscosmos , warned that sanctions against Russia (mostly those over the 2022 Russian invasion of Ukraine ) could result in the International Space Station crashing. Since the Russian section of the space station is the one that provides propulsion (although it is built to rely on the power generated by the other sections), this was taken seriously and as of when this was posted, NASA was trying to come up with alternative stabilization strategies in case the situation worsened. There was also a recent report of some 600 kg space rocket debris found in Brazil. The title text makes a similar joke. While the increase in chances of death by a bear attack are greater when going outside than the decrease in chances of death by cardiovascular disease, by getting out to exercise, it is incorrect to combine them in this way, since cardiovascular disease has a much higher starting chance of death, and reducing it by 30% has a much more significant effect on overall life expectancy than quadrupling the very very small chance of death by bear attack. At least for the majority of us who don't live in or near wild bears' natural habitats. The "280% increase" of the title text is also an error, though perhaps not for reasons that are obvious at first (for instance, the correct calculation is not "300% − 30% = 270%"). To "increase by 300%" means multiplying the probability by (1 + 3.0) = 4.0, while to "decrease by 30%" means multiplying by (1 − 0.3) = 0.7. Combining these means multiplying by both, for an overall change of 4.0 × 0.7 = 2.8, or 280%. However, this result means the risk has increased to 280% of its old value, not by 280%. And in any case, it is still not valid to simply combine two changes in wildly different risks like this. The odds of an event is the probability that it happens divided by the probability that it doesn't happen. People often express odds as a ratio (e.g. the odds of rolling a 6 on a 6-sided dice might be expressed as 0.16777... : 0.83333..., or equivalently as 1:5), but it is important to note that such ratios are not odds ratios (it would be fitting to call this a "probability ratio", but this terminology is not standard). An odds ratio is the odds of event O happening, given that some other event E has occurred, divided by the odds of O given that E has not occurred. O is sometimes called an "outcome" and E is sometimes called an "exposure", because people are often interested in comparing things like the odds of getting lung cancer (O) given that you smoke (E) to the odds of getting lung cancer given that you don't smoke, as a way of measuring the extent to which exposure to E influences outcome O. In the case of the comic, the outcome variable O is the event of getting a head injury from falling spacecraft debris, and the exposure variable E is the event of spending H hours per day outside, for various values of H. The comic appears to be saying that for each value of H, there are two options for E: either you spend H hours per day outside or you never go outside. So for small values of H (e.g. 1 hour per day), the comic is saying that the event of being hit by spacecraft debris is more or less independent of the event of spending H hours per day outside, which is to say that the odds of being hit is more or less the same regardless of the choice you make between spending H hours per day outside and never going outside. Hence the dot on the 1-hour bar is close to 1, because the two odds are more or less equal (the dot appears to represent an average estimate of the odds ratio). Note that when calculating the odds ratios for this comic, the odds in the denominators are always the same, as they are the odds of being hit given that you never go outside, which does not depend on H. So when the comic says that the odds ratio is above 3 for H={11+ hours per day}, it is effectively saying that the odds of being hit when you spend this much time outside is a bit more than 3 times the odds of being hit when you spend 1 hour per day outside. Suppose the probability of being hit is: P when you spend 1 hour per day outside, and Q when you spend 11+ hours per day outside. The odds of being hit under these two exposures are P/(1-P) and Q/(1-Q) respectively, and because the odds ratios have equal denominators, the comic is saying that Q/(1-Q) = kP/(1-P), where k is a bit more than 3. If we rearrange this to get an expression for Q, we get: As P is negligibly small, 1-P is very close to 1, and P+(1-P)/k is very close to 1/k. Thus Q is very close to kP (i.e. a bit more than 3 times P), meaning that the probability of being hit when you spend 11+ hours per day outside is still negligibly small. Thus, the comic's suggestion that we spend 4 hours or less outside based on the estimated odds ratios is extremely misguided. [A chart is shown. Above the chart there is a heading, with a subheading below it:] Odds ratio for head injuries from falling spacecraft debris (Monte Carlo Simulation) [The chart is rectangular with the X-axis labels above the chart with numbers from 1 to 5. These are places over vertical lines. The first at 1 is black, the other four are light gray. There are three smaller light gray ticks between each set of lines, and one on either side of the first and last. The distance between lines gets smaller and smaller towards the right, probably logarithmic.] X-axis: 1 2 3 4 5 [The Y-axis is not scaled; there are no ticks or lines. Instead it just gives five labels from top to bottom. Above those labels there is an arrow pointing to the top one with a label above explaning the axis.] Hours spent outdoors per day Y-axis: 0 (ref) 1 2-4 5-10 11+ [Aligned with each of these five divisions of the Y-axis there is a dot. The top one is placed on the solid line under 1 as a reference point. The other four dots all have long error bars, with the dots at the center of these. The second dot is a bit to the left of the solid line, with the error bar going almost to the left edge of the graph and halfway to the first light gray line to the right. The third dot is located halfway between the solid and the first light gray line with the error bar just crossing the solid line, and almost reaching the gray line. The fourth dot is about a third way between the first and second of the gray lines, with the error bar crossing both these lines. The fifth and last dot is just past the second gray line, with the error bar crossing both that, going more than half toward the first gray line, and also just past the third gray line. On the same height as the two bottom dots, there are asterisks just right of the edge of the graph.] * * [Below the panel there is a caption:] Our new study suggests that spending more than 5 hours outside significantly increases your risk of head injury from spacecraft debris, so try to limit outdoor activities to 4 hours or less.

Rejected Question Categories

Rejected Question Categories

https://www.xkcd.com/2600

https://www.explainxkcd.com/wiki/index.php/2600:_Rejected_Question_Categories

In What If? 2 (xkcd.com/whatif2), I answer ridiculous questions sent in by readers about everything from volcanoes to spaceships to soup. Here are a few of the common types of question that I did not answer: [In separate boxes for each category] [In row 1:] People cheating on homework: What if I made a pendulum by hanging a rock on a 2.75 meter string? What would its period be in seconds? (Show your work!) Medical advice: What if you got a scratch and the next day your hand looks like this [ 📎 attachment ]? Should you see a doctor or what? Personal: Why don't the squirrels in my yard like me??? [In row 2:] Spam: Do you want to meet lonely singles in your area tonight? Phishing: Have you recently been the victim of phishing? To check, log in to your account by clicking here . Requests for help with a crime: Using modern science, what would be the fastest way to get through this bank vault door? [ 📎 blueprints] [In row 3:] Unanswerable: Why am I me and not someone else Vague: What is going to happen? (Be specific) Vague+Ominous: Will I have to start worrying about spiders after Tuesday? ?????: Hi, we're lonely singles in your area, and we're wondering what would happen if we shot a nuclear bomb into a volcano! [partially cut off horizontally:] Click here to log in and tell us

This comic shows the categories of questions he claims to have received, but rejected to use in his book, giving an example question for each category. In typical xkcd fashion, these begin out by being plausible, although often unlikely to have been submitted as a what if? question, moving in to more and more absurd types of questions, especially with the last question, that appears to be a combination of all previous categories and is therefore marked "?????" The title text refers to the launch date of the book September 13, rendered in the American style 9/13. This format can be confusing to non-Americans, although usually not when the date is larger than 12, since it would then appear to reference the 9th day of the 13th month. This "13th month" was, however, referenced in the first comic about the book: 2575: What If? 2 . See also Randall's take on the date format, ISO 8601 , in 1179: ISO 8601 . Randall then continues the title text by referencing the second to last category with vague ominous questions. The example question here asks if there is need to worry about spiders after Tuesday. So Randall notes that the release date, 5.5 months after the release of this comic, is of course assuming anyone will survive past next Tuesday (2022-04-05). Tuesday has been notably referenced in 277: Long Light , 564: Crossbows , 1099: Tuesdays and most notably in 1245: 10-Day Forecast , where it seems that the last day ever will be a Tuesday. Tuesday is the second day of the week, and notably, the Tuesday of the week following the publication of this cartoon (April 5th, 2022) was the Day of the Spiders. In What If? 2 (xkcd.com/whatif2), I answer ridiculous questions sent in by readers about everything from volcanoes to spaceships to soup. Here are a few of the common types of question that I did not answer: [In separate boxes for each category] [In row 1:] People cheating on homework: What if I made a pendulum by hanging a rock on a 2.75 meter string? What would its period be in seconds? (Show your work!) Medical advice: What if you got a scratch and the next day your hand looks like this [ 📎 attachment ]? Should you see a doctor or what? Personal: Why don't the squirrels in my yard like me??? [In row 2:] Spam: Do you want to meet lonely singles in your area tonight? Phishing: Have you recently been the victim of phishing? To check, log in to your account by clicking here . Requests for help with a crime: Using modern science, what would be the fastest way to get through this bank vault door? [ 📎 blueprints] [In row 3:] Unanswerable: Why am I me and not someone else Vague: What is going to happen? (Be specific) Vague+Ominous: Will I have to start worrying about spiders after Tuesday? ?????: Hi, we're lonely singles in your area, and we're wondering what would happen if we shot a nuclear bomb into a volcano! [partially cut off horizontally:] Click here to log in and tell us