Future Archaeology

Explanation:
This Wednesday comic is a direct continuation of the previous comic 1747: Spider Paleontology from Monday about a time-traveler (the black floating energy Sphere) who has come back from far in to the future to see spiders (only known from fossils in their time). See 1747: Spider Paleontology for a more complete explanation of this part of the joke. This series ended with this comic. Both comics in this series have titles of a noun followed by a field of research.
Since Megan and Cueball now have access to the Sphere from the future they ask if it knows who will win the election. This is a reference to the United States elections, 2016 where the very controversial Donald Trump was up against former United States First Lady Hillary Clinton , who also had several controversies going on. This comic was released about three weeks before election day. It is likely one of the most discussed elections ever, especially in the rest of the world outside the US, where especially European leaders have made it clear that they are against Trump. That was mainly earlier on, before they realized he might actually stand a chance. Of course anyone interested in any election would be interested to hear from the future how it went, but this particular election may interest a larger proportion of the world population than any prior election. (The election was the subject three weeks later the day before the election where Randall endorsed Hillary directly in 1756: I'm With Her .)
Sadly for Megan and Cueball, the sphere has come back from so far in to the future, that even spiders have gone extinct. (Whether humans also have is unclear, see discussion about this in 1747: Spider Paleontology ). The Sphere makes this clear by stating that its civilization hardly know anything about our era and they know little about our history and culture. (And by the way it only came back for the spiders, anyway).
The idea is that history is filtered in similar fashion to fossils.  What is contemporaneously important, like a spider's web , dinosaur feathers (see previous comic), or the United States presidential election may not survive. The Sphere tells them that only two written accounts have been reconstructed (note that they are not found in their entirety). And they do not know if they even represents real events or myths. One of the two is indeed a myth, as it is about a man building a boat to survive a great flood. Megan recognizes this as being about Noah and his famous Ark from the Genesis flood narrative , as Cueball refers to. The other is a reference to a popular pop song.
The joke is that, in the future, the 2000 Aaron Carter hip hop song " That's How I Beat Shaq " ( lyrics and video ) is considered as valuable a historical document when researching humans as parts of the Bible .
While secular historians consider the story of the Flood to be mythical, they still use it to infer facts about the early history of the Middle East, simply because there are a fairly small number of texts surviving from that era. "That's How I Beat Shaq" is, likewise, a fictional story including some true elements; it's just that as long as there are abundant sources documenting life in the year 2000, there's no reason to consult the song in any historical context. Yet it is the latter story that the time traveler assumes to be a clearly religious one, while seeing the former as a relatively straightforward survival story. A further layer of humor is that "That's How I Beat Shaq" is an archetypal David and Goliath story—the story of David and Goliath of course being a Biblical one as well.
In fact the Spheres civilization believes Shaq ( Shaquille O'Neal a professional basketball player 2.16 m (7 ft 1 in) tall) to refer to a god, which was then defeated by Aaron, a 14 year old (and rather small kid) at the time of the release of his single in 2001. He beats Shaq on the basketball court one on one, so although this is a David vs. Goliath story it is not a fight till death. But to Aaron and his basketball fan friends, Shaq is probably seen as kind of god. Megan comments that the pop song may have been mangled by the eons .
The title text expands on the joke by letting the Sphere explain that the only connection they have found between their two historical documents is via the biblical story of Moses . As Moses is also one of God's chosen prophets and leaders, like Noah and Abraham before him, these two stories appear close together in the Bible, though not close together chronologically, and it would be likely that their document with the Flood story also has some parts about Moses. Moses had an older biological brother named Aaron and the Sphere's civilization has hastily concluded that Moses' brother and Aaron Carter are one and the same. According to the Bible, God parted the Sea of Reeds (commonly mistranslated as Red Sea) for Moses and the Israelites . This is often referred to, either erroneously or out of simplification, as Moses having parted the Red Sea. Along with Noah's Flood, this is one of the two major times in the Bible that God effects grand change on a body or bodies of water.
The Sphere asks Megan and Cueball if it is true that Aaron (Carter's) brother Moses did part an ocean. Megan decides to refrain from trying to explain this, having already in the previous comic realized how hard it is to explain spiders to someone who is a fan, but has never heard of spider web, and thus just states yes, yes exactly. Of course according to the Bible she can say yes to the question about Moses parting the water, as long as she does not say anything about the connection with Aaron Carter.
There appears to be a major flaw in the comic on the fact that the Sphere speaks perfect English, and understands Megan and Cueball. If they only have two written accounts from our time, why do they then speak English? Especially since they seem to come from another planet and are thus likely not humans (see discussion of the sphere in the previous comic). Of course if they are humans and have come from Earth (maybe traveled away), they may just have retained the English language. But given the fact that young people today probably would not understand their own grandparents' grandparents, and that the Sphere is from so long into the future that Megan calls it eons, spiders are extinct, and only two texts have survived, it should be impossible for the language to have stayed the same. Alternatively they have also recovered some video clips, but then it would be strange the Sphere did not mention this. A final solution is that the Sphere's civilization is so advanced that it can learn the language instantly by just being in the room with other beings, simply reading it from their mind. Given the fact that it seems the Sphere has come to Earth from another planet, and has the ability to travel in time, this last option may not even be so far-fetched.
This comic was published the day after the what if? Flood Death Valley , thus referring indirectly to a new possible flood history. It was the first what if? post in almost three months, the longest break between two post during 2016 (and third longest of all time at the time of its release), and it thus seems realistic that there should be some kind of connection between that and this comic. A later comic ( 1750: Life Goals ) also referenced this what if? post more or less directly.
In this comic Randall manages to combine no less than four of his favorite recurring subjects with time travel , spiders , politics and religion .
[The Sphere, a time-traveler depicted as a solid floating black energy sphere surrounded by six outwardly-curved segments (first seen in the previous comic), is floating in front of Megan and Cueball who is walking after it towards the right part of the panel. The Sphere looks like this in all panels, but in the zoom in from panel two more details can be seen. A voice emanates from the Sphere.] Megan: Since you're from the future, do you know who wins the election? Sphere: Haven't the faintest idea. Hardly any text has been recovered from your era, so we know little about your history and culture. Sphere: We're mostly here for the spiders, anyway.
[A close-up of the Sphere, still depicted as a black sphere, but not perfectly round at this zoom level and also clearly with some white dots in the dark area. It is still surrounded by six narrow rays with irregular dots between the rays.] Sphere: There are only two written accounts we've reconstructed. Sphere: We don't know whether they describe real events or myths.
[The Sphere is now on the left side of Megan and Cueball who has stopped walking and has turned to look at the Sphere.] Sphere: One is a story about a man who built a boat to survive a great flood. Megan: Oh yeah. Noah. Cueball: We do like our flood narratives.
[The Sphere has drifted further away from Megan and Cueball.] Sphere: The other is an account of how a man named Aaron Carter defeated a god named Shaq. Megan: That one may have been mangled a bit by the eons.


Mushrooms

Explanation:
Cueball is looking at a mushroom , contemplating how weird they are, when Megan adds another layer to their weirdness by supplying the trivia that evolutionarily , mushrooms (which are basidiomycete fungi ) are closer to the animal kingdom than to plants on the tree of life . (Note that, technically, mushrooms themselves are only the fruiting bodies of the fungi. A mushroom is only part of a fungus, in the same way an apple is only part of a tree. The majority of the fungus grows beneath the soil, in a part of the fungus called the mycelium , which is composed of root-like structures called hyphae .)
Both animals and fungi are part of the opisthokont group of eukaryotic organisms, while plants are in the archaeplastida group of eukaryotic organisms with the green and red algae .  This surprises Cueball, as he, like many people, is likely to think of mushrooms as plants, as they are "grown" just like other crops. Even scientists, before the 1960s, considered fungi to be 'plants'; it took DNA-based studies in the 1990s and 2000s to 'seal the deal' and place the fungi with the animals, and not the plants. But fungi do not perform photosynthesis , and therefore do not need sunlight to grow. Instead, they get their energy from other living matter, either live (parasitic mushrooms) or dead (e.g. manure; saprobic mushrooms). Edible mushrooms like Agaricus bisporus (or white mushroom) are saprobes, farmed in caves . The body plans of fungi are also utterly unlike those of plants. There are a few plants that don't do photosynthesis, such as the parasitic flowering plant Monotropa uniflora . But these plants otherwise look like, and are built like, plants, and don't look or grow at all like fungi. Ironically, many plants, both photosynthetic and nonphotosynthetic, depend on root-associated mycorrhizal fungi for their survival and growth.
Megan then walks away, and Cueball, after pondering the mushroom a while further, gets up and walks away too. But as soon as Cueball has his back turned the mushroom growls after him. Cueball spins around to look back at the now again silent mushroom. This is a bit of absurdist humor; while mushrooms are technically more animal-like than plant-like, they are still so far removed from animals they wouldn't have any of the body parts needed to growl. [ citation needed ] For that matter, most animals lack the parts needed to growl.  Cueball's shock and astonishment is quite justified, and maybe it was just his imagination running wild after Megan's trivia. The reader is left to wonder what Cueball's next move will be - especially, those readers who have ever felt, or indulged, the urge to stomp mushrooms.
Another interpretation of the mushroom's growling is that mushrooms might be "fake" animals disguising as plants. The mushroom seems to be a plant, and acts very plantlike until Cueball looks away. The mushroom might have growled because it was planning on killing Cueball in a sort of "kill the witnesses" action.  This comic might be hinting that mushrooms are evil and plotting the downfall of humanity under the disguise of "harmless" plants. Or, simply, mushrooms want to mess with other living things.
The title text takes this further, by stating that mushrooms are technically a type of ghost . Maybe because they arise from decaying remains. The title text may also refer to 1240: Quantum Mechanics or 1475: Technically , suggesting caution when dealing with a statement preceded by "technically." It may also refer to the other name of Monotropa uniflora , "ghost plant" which hosts are certain fungi.
The title text might also refer to the behavior of ghosts (called Boos) in the Super Mario series, in that they only act or move when the player is facing away, as does the growling mushroom.
[Cueball is squatting in front of a group of four mushrooms (two tiny, one small and one large), touching the top of the nearest and largest mushroom with a finger. This mushroom has several small dots, which becomes more visible in later panels. The other three mushrooms do not appear to have these dots. Megan is standing behind him looking on.] Cueball: Mushrooms are so weird. Megan: You know, evolutionarily, they're closer to being animals than to plants.
[Megan starts walking away as Cueball now leans on the ground with the hand he touched the mushroom with. Only the large mushroom is visible in this and the rest of the panels.] Cueball: ...Really? Megan: Yup!
[In a frame-less panel Cueball still squats in front of the mushroom, now resting his hand on his knees.]
[Cueball stands up looking down at the mushroom.]
[Cueball is walking away as the mushroom makes a sound indicated with several small lines emanating from the top of the mushroom along with a regular speech line.] Mushroom: Grrrr
[Cueball snaps around to look at the mushroom again, standing in a prepared state arms slightly out and legs spread out as well.]


Life Goals

Explanation:
All visible goals except the last one on this to-do list feature one or more strange words containing an excess of the last three letters of the alphabet (X, Y and Z), often using several of them in the same words, even several of the same rare letter in a row. (See Table of life goals below).
All of these words can be looked up in the English version of Wikipedia, but only a few are common nouns , three of them weird animal names, the rest being proper nouns , i.e. persons names (fictional or artist) or obscure names for places or video games. The first goal is the one with fewest of these letters, only using two x's, and only the first word is strange, Skrillex being the artist name of a musician. All later entries have at least three of these letters, which are most often used in very strange, often difficult-to-pronounce, words.
The punchline, in the final and ninth goal, expresses that the writer of this list often uses these unexpected and bizarre words in Scrabble games, which exasperates his opponents to such a great extent that he has yet to finish a game without getting punched. All of these words would theoretically earn a player many points in Scrabble, but outside of casual play it is not allowed to use proper nouns (see Scrabble points below).
In the title text, a reference is made to the fact that none of these goals have been checked off yet. It also turns out that it is indeed Randall's list, since the writer of the list did (at least) manage to check off the goal Make something called xkcd early. Sadly there are neither y's nor z's nor even more than one x in that four letter combo.
This comic was published the week after the what if? Flood Death Valley , which referred directly to the city Zzyzx in one of the pictures. It's the second comic in that week after the what if? post that references it more or less directly, the previous one being 1748: Future Archaeology . It seems likely that Randall created this comic after doing research for this what if? post, and came across the city Zzyzx as the shortest way to dig a channel to flood Death Valley.
All of these strange words would theoretically earn a player the prize of many points in Scrabble (Go to the table of words below). However, most of them would not be found in SOWPODS (the combined list of all words valid in either British or North American Scrabble tournaments).  Also, many include too many X's, Y's or Z's (there's 1 X, 2 Y's, 1 Z in a standard set), meaning at least one would have to be substituted for a blank (which is not worth any points). Some words would also be very difficult to play in reality, since there are only 7 letters in a Scrabble hand, so they could only be played in extremely rare circumstances (there are only a couple of ways to play MUZQUIZOPTERYX: for instance, from MU and OPTER; or MU, QUIZ and ER; or an astonishingly unlikely set of crossing letters). Many are long enough that, in theory, they could net the player the additional 50 point bonus for using all seven letters in a hand if played right.
[A to-do list with a caption above:] Life Goals ☐ Meet Skrillex in Phoenix ☐ Study zymurgy ☐ Get a pet axolotl named Hexxus ☐ Observe a syzygy from Zzyzx, California ☐ Port the games Zzyzzyxx and Xexyz to Xbox ☐ Publish a Zzzax/Mister Mxyzptlk crossover ☐ Bike from Xhafzotaj, Albania to Qazaxbəyli, Azerbaijan ☐ Paint an archaeopteryx fighting a muzquizopteryx ☐ Finish a game of Scrabble without getting punched


Movie Folder

Explanation:
Cueball is looking through Black Hat's downloaded movies, which are all adaptations of non-literary works, improbable sequels, and/or crossovers between very disparate properties. Cueball reacts with increasing incredulity to Black Hat's collection, while Black Hat casually responds with equally unlikely (non-)explanations. Knowing Black Hat, his movie folder is deliberately weird just to provoke this kind of reaction.
In the real world, there are movies which can provoke similar shock. For example, many successful films get direct-to-video (or, now, direct-to-digital ) sequels and spinoffs, often featuring none of the original cast and which get very little marketing. Therefore, someone might be surprised to know that there's an American Psycho 2 , a Starship Troopers 3 , a Dr. Dolittle 5 , or a Bring It On 5 . Randall previously made fun of the proliferation of direct-to-video sequels in What If: Twitter Timeline Height , with at least 27 Land Before Time films (in reality, there were 14).
Another source of weird titles are mockbusters . When a film uses a public domain property as its basis, or a title that is too generic to trademark, other studios will simply create their own films and pretend that they're a sequel to the more famous film. Examples include Titanic II , Troll 2 , Troll 3 , the other Troll 3 , Day of the Dead 2: Contagium , Alien 2: On Earth (not to be confused with the real sequel Aliens ) and War of the Worlds 2: The Next Wave .
Marketing wheezes have also produced some crossovers almost as unexpected as those in the comic — Abbott and Costello Meet Dr. Jekyll and Mr. Hyde , Scooby-Doo! WrestleMania Mystery and Jesse James Meets Frankenstein's Daughter are all real films.
A similar setting with Cueball and Black Hat also discussing movies was seen in 493: Actuarial . Back then Black Hat was still reading newspapers. Black Hat has previously given similar non-answers to long series of questions from Cueball in 908: The Cloud and 1159: Countdown .
Another type of comic where movie titles needs to be guessed from strange versions of the title was previously used in the Synonym Movies series.
[Black Hat is sitting in an armchair, with the right arm on the armrest and looking at his smartphone held in his left hand, when a voice from behind him (off-panel left) addresses him. It turns out in the next panels that it is Cueball.] Cueball (off-panel): Your movie folder is so weird . Where do you find all this stuff? Black Hat: Dunno. Black Hat: Around.
[In an frame-less panel Cueball is seen sitting in an office chair at a desk facing left. He is looking at Black Hat's computer while typing on the keyboard which is on a shelve lower than the regular desk surface. Black Hat replies to his queries from behind him off-panel right.] Cueball: Lorem Ipsum: The Movie? Cueball: Titanic XCVIII? Black Hat (off-panel): That series gets good when they start hitting the reef created by all the previous wrecks.
[Cueball leans in closer to the screen.] Cueball: Debbie Did 9/11? Cueball: Time Jam: A Connecticut Huskie on King Arthur's Court? Black Hat (off-panel): Really underrated Space Jam sequel.
[Zoom in on the scene so nothing beneath the keyboard is visible. The screen and Cueballs head almost spans the width of the panel.] Cueball: Harold and Kumar Go to Howl's Moving Castle? Cueball: A Million Random Digits with 100,000 Normal Deviates? Black Hat (off-panel): That's the original-the book was a novelization.
[Back to Black Hat sitting in the chair as in the first panel, but leaning a bit further back and the arm on the armrest has been moved closer to him.] Cueball (off-panel): Michael Bay's The Vagina Monologues!? Black Hat: It's pretty good, despite all the CGI explosions.


Interplanetary Experience

Explanation:
This comic lists ten celestial bodies : most other planets , the dwarf planet Pluto , as well as two moons , the Earth's Moon and Titan (the largest moon of Saturn ). It then asks what places on Earth people could go to for a real Interplanetary Experience , as if they were explorers on these planets. It turns out that none of these ten other worlds are very nice to visit...
This is a parody on organizations that in preparation for future planetary exploration organize half-realistic experiments in human behavior on other planets, trying to emulate or mock-up - often on low budget - the conditions in which future explorers are to live and work. For this purpose, they build mock-up bases, habitats etc. in places that look like other planets or have the environmental conditions somewhat similar to other celestial bodies' surfaces. They seek out desolate places like deserts or polar regions for this purpose.
In this comic Randall tries to identify places on Earth that actually have environmental conditions as close to these other worlds' as can be possible on the surface of the Earth. Some of the places suggested by Randall are borderline-survivable for a human, but most will kill you extremely quickly without a lot of high-tech gear - whether through severe hypothermia (freezing), conflagration (fire), crushing (high pressure), or from violent winds.
Basically, nowhere in the solar system , except Earth, is even close to survivable (and there is actually only a very limited amount of Earth's surface where humans can actually live permanently). There is no planet or moon with a breathable atmosphere, or where the temperature stays within the human-tolerable range of roughly −20°C to 40°C (−5°F to 105°F, 250-310 K). It is also only with really good clothing and a place to stay at night that humans can live in a place much colder than 10°C for longer periods. The only place humans have so far ventured off-Earth is the Moon, and only during lunar morning while wearing thick pressurized spacesuits.
Some celestial bodies, like Venus and Jupiter , may never be visitable by humans without either huge advances in material science or full-scale terraforming (for Venus). Some places, like the centers of any planet (for example, the gas giants or even Earth itself), will probably never be visited, even by robots. (The title text suggests what happens when falling towards the center of a gas giant).
Below is a list going through the seven suggested places on Earth. Due to the low pressure and temperature on the top of Mount Everest it is mentioned no less than three times, but using different time of day to represent different celestial bodies. In the first entry it even takes care of three in one go. Two of those are the Moon and Mercury, but for both only on their night side facing away from the sun. They are thus each mentioned twice, as there is a huge difference in environmental conditions between the sunlit faces of these two and their night sides. On the other end of the temperature scale are mentions of lava and a blast furnace ; also high pressure environments are suggested to simulate other planets. The last goes for the gas giants, which are all mentioned together in the last entry.
The two groupings explains why there are only seven places mentioned for ten celestial bodies. The reason that the Moon is mentioned is of course that it is the closest companion to Earth and that we have actually visited it. That the only other moon mentioned is likely because it is the only really cold celestial body that actually has an atmosphere as well as a surface humans could stand on. But there are many other large moons that would be interesting to visit, like the Galilean moons especially Europa . But that could probably be compared to being on Pluto, except the sun is a bit larger. That Pluto is included as the only dwarf planet is probably because it was still a planet when Randall was a kid (see 473: Still Raw ) and is the most recent (new) celestial body visited by a space probe at the time of release of this comic. This was celebrated by Randall in 1551: Pluto .
The title text is just a continuation of the last entry about falling down through the atmosphere of a gas giant, and it is also explained in the table below. This was also explored in What If? Jupiter Submarine .
The dwarf planet Pluto is a small icy rock so far away from the Sun that it practically makes no difference if it is day or night, the Sun is just the brightest star in the sky of Pluto's "day" side. But for both the Earth's Moon and Mercury (the innermost and smallest planet of the solar system ) it makes a huge difference, which is why there is both a day and a night experience mentioned for these two celestial bodies (see below). Although they are very much closer to the Sun than Pluto, this makes no difference during their night time (when they face away from Sun). They are both relatively small, rocky bodies with practically no atmosphere and relatively slow rotation. Therefore their surfaces not illuminated by the Sun will cool down to very low temperatures (around -170 °C, -290 °F, 100 K), making their nighttime hemispheres desolate, dark and cold places. Randall proposes the summit of Mount Everest (the tallest mountain on Earth) as the place that will emulate the conditions most closely. It is a rocky, desolate and cold place. Even though it is not the coldest place on Earth, it is the highest point on land, therefore it has the lowest atmospheric pressure. It cannot be compared to the near-zero pressure and 100 Kelvins conditions on the aforementioned bodies, but it is as close as you can get on Earth. The top of Mt. Everest has an air pressure just 1/3 of what it is at sea level, and the oxygen levels are so low that they are barely survivable, although a few people have reached the top without oxygen tanks , but others have died after losing their oxygen supply, making it as close as you can get on Earth to the near-vacuum found on these worlds.
As explained above, Mount Everest is as good an emulation of the Moon surface at night as you can get on Earth. During the Moon's day, its surface gets about as much solar radiation as Earth at noon, because both bodies' distance from the Sun is almost the same. The Earth's atmosphere, however, stops most of the Sun's ultraviolet radiation . A tanning lamp is a device emitting mostly ultraviolet radiation for the purpose of artificial tanning ; here it is used to augment the filtered Sun's radiation in an attempt to emulate the Moon's daytime conditions better. Since the Moon does not have any atmosphere it is hard to discuss the temperature experienced on the Moon, but still the surface of the Moon reaches temperatures above water's boiling point (100°C or 212 °F) during the day with an average daytime temperature of the Moon at 107°C (224.6 °F). This effect will not be very well emulated on top of Mount Everest or even in the hottest (non-volcanic) place on Earth's surface that reaches 53.9°C (129°F) — see the what if? Flood Death Valley .
Mercury's surface never quite reaches lava temperatures (if it did, it would be molten), but it gets close. At noon, Mercury's equator reaches 420°C (800°F, 700 K). Lava is a liquid usually at temperatures from 700 to 1,200 °C (1,300 to 2,200 °F, 970 K to 1470 K) but depending on what type of rock it's formed from, lava can erupt at temperatures as low as 500°C-600°C (930°F-1100°F, 770–870 K). Standing on a volcano on a partially solidified lava flow (which, it goes without saying, is incredibly dangerous) would expose you to similar temperatures.
Near the poles, Mercury's surface temperature is always very low as the axial tilt is almost zero, meaning that the poles do not get much direct sunlight and their temperature is constantly below −93 °C (−136 °F, 180 K).
The average surface temperature on Venus is around 470°C (870°F, 740 K) (enough to melt lead at 327 °C (620°F, 600 K), which is the usual comparison ), and the pressure is 92 bar (by comparison, pressure on earth is only about 1 bar). A blast furnace is a bit too hot — the blast itself is 900 °C to 1300 °C (1600 °F to 2300 °F, 1170 K to 1570 K), and they can reach 2000 °C — but either temperature is enough to kill you in seconds. As the blast furnace would emulate Venus' temperature but not pressure, Randall proposes that a daring volunteer wear a hypothetical heat-shrink wetsuit. A wetsuit is an elastic garment worn mostly over the whole body by swimmers, divers etc. Heat-shrink tubing is an elastic tube made of a material that shrinks when heated, used to provide extra insulation and mechanical or environmental protection in electrical and electronics work — you put a length of tubing over your wire, connector, or a joint and heat it with a hot air gun, making it shrink and crimp over your device. A hypothetical heat-shrink wetsuit worn while sitting in a blast furnace supposedly would shrink rapidly in the extreme temperature, exerting great pressure on your body, thus emulating Venus' surface atmospheric pressure. In other words, do not go to Venus!
Again use Mount Everest's thin atmosphere and very cold temperatures to emulate the planet, but Mars' dusty, greenhouse-gas-containing atmosphere means it's not as cold as Mercury at night, nor as hot as the Moon during the day. Also the sun is much farther from Mars than from the Earth/Moon system, but much, much closer than Pluto, so it should be colder than the day side of the Moon. But the Sun still looks like a sun rather than a star from Mars, unlike on Pluto. The sunset will also make the sky reddish-purple, similar to the way the Martian sky often looks .
Titan, the largest of Saturn moons (and one of the largest moons in the solar system) is one of the promising worlds for life.  Given that its surface temperature is −180°C (−290°F, 95 K), that says a lot about how inhospitable the rest of the solar system is. The chemistry of the planet is interesting — there are lots of nitrogen compounds and hydrocarbons and the atmosphere is mostly nitrogen and methane. It has been confirmed that methane lakes exist on Titan's surface. It thus follows that there is likely also some precipitation of methane "snow", similarly to how water forms lakes and falls down as sleet on Earth. Similar compounds are produced by rotting material in swamps , hence the comparison to a cold Siberian swamp. Due to the global warming large area of the tundra in Siberia that used to be permanently locked in permafrost are now heating up enough to release these gases . It might thus be possible to end up waist deep in one of these "heated" swamp areas due to the resulting outgassing . Sadly for the global temperature this outgassing just increases the release of greenhouse gasses, making the global warming increase even faster. This may very well be the reason Randall chooses to mention it here, as another call back to recurring theme of Climate change and to the recent comic 1732: Earth Temperature Timeline . One key difference though is that on Earth, swamps are mostly water. On Titan — if they exist at all — they're liquid methane. Siberia also has some of the most extreme temperature differences on Earth, while Titan is just consistently cold. The coldest place in Siberia is the Pole of Cold , the coldest point in the Northern hemisphere having reached −71.2 °C (−96.2 °F, 202 K). Not quite Titan levels of cold, but certainly deadly enough. But in such cold places there would be no outgassing, so on Earth it is not possible to have both the cold and the outgassing.
Note that it is Jupiter to Neptune thus including also Saturn and Uranus . They are under one called gas giants for a reason. All the planets are very cold and have stormy weather (Uranus is the least active, and Neptune is the most active) and extreme temperature and pressure gradients.  On the edge of the atmosphere, conditions aren't much different from space, but as you fall in, the temperature and pressure rapidly increase past the freezing point (allowing clouds of ice and water). This environment is simulated by jumping out of a high-altitude balloon (low pressure and cold) and falling down into an Antarctic Ocean winter storm, a very cold and violently windy place. The storms on the gas planets can be much more violent than any storm on Earth. On Neptune the storms can reach 2,100 km/h (580 m/s, 1,300 mph), whereas the Great Red Spot of Jupiter only reaches 430 km/h (120 m/s, 270 mph). The highest wind speed on Earth (outside tornadoes ) has been measured at 408 km/h (113 m/s, 253 mph), and that was only the gusts.
The title text continues the last entry in the main comic, so this explanation is also a direct continuation of the above entry. The extreme temperature and pressure gradients mentioned do not stop when the atmospheric temperature and pressure increase beyond water's freezing point.  Soon the temperature reaches past the boiling point, and on up to thousands of degrees and unimaginably high pressures, increasing further until reaching the central core. The cores of Neptune and Uranus most likely consist of rock (superheated silicates, iron and nickel) or in the case of Saturn and Jupiter of liquid metallic hydrogen , where the extreme high-pressure and temperature causes hydrogen to behave like a metal. The suggested simulation of this environment is to fall into a super hot bath tub that falls into the burning engine room of a ship that is sinking, and thus is about be crushed by the water pressure of the deep ocean.  This is the closest representation of the pressure and temperature conditions of the inner parts of the gas giants that can be imagined on Earth, but of course the cores of these planets are far, far more inhospitable than the scenarios mentioned above. Descending into Jupiter was also explored in the what if? Jupiter Submarine .
[Caption above the panel:] Where to go on Earth to get the Interplanetary Explorer Experience
[A chart with seven rows with celestial bodies on the left side of seven lines and a description on the right side. The first entry has three celestial bodies in two rows, the rest are in one row, although the last entry encompasses a list of planets. Four times the day/night side of the celestial bodies is mentioned in brackets.]
Pluto, Moon (night) Mt. Everest at night Mercury (night) Moon (day) Mt. Everest at noon under a tanning lamp Mercury (day) A lava flow on a volcano at noon Venus A heat-shrink wetsuit in a blast furnace Mars Mt. Everest at sunset Titan Waist-deep in an outgassing Siberian swamp Jupiter-Neptune Jumping from a high-altitude balloon over an Antarctic Ocean winter storm


Thumb War

Explanation:
Two small children, one a small Black Hat , sitting among their toys are playing thumb war . This is a common game for children, in which two players hold hands and attempt to pin each other's thumb down. The game is often started with both players chanting "one, two three, four, I declare a thumb war." In some variations, the chant continues counting up by an additional set of four, with a rhyme. Once the opening chant is complete, the game consists of trying to pin the opponent's thumb down. A pinned thumb must be held down for long enough to complete a count of four, or to complete the closing chant, "one, two, three, four, I won the thumb war".
The standard concept is subverted here: Young Black Hat interprets the simulation of hand-to-hand combat with thumbs differently, comparing it with real conflict. He shows this in further lines, invented by himself.
The second rhyme, "finger guns proliferate," is a pun on the finger gun gesture and describes small arms proliferation - the spread of black-market weapons which often comes with war as captured and smuggled guns make their way into the hands of paramilitary groups. Black Hat transfers this into the "thumb war universe", introducing finger guns into the thumb-to-thumb combat.
The third rhyme continues the counting until twelve and mentions digits as in fingers, and states that they cannot protect themselves. This may be implying an imposition of firearms regulation or arms control as a response to the small-arms proliferation in the previous verse, or the defenseless nature of noncombatants in war.
In the last line Black Hat states that, even though this thumb war goes on and on, the "thumb U.N.", the thumb war universe equivalent of the United Nations (UN), won't intervene. In real life the UN would try to put an end to a given war by using diplomatic power and has the mandate of using (blue-helmet) peace forces in war zones to put an end to violence and give out a mandate to nations so that they can intervene in some crisis on their own behalf.
The thumb war game in Black Hat's version is instead a quite cynical portrayal of our world, criticizing the "might is right" mentality that is the sad reality of our globe, and the government of the world by the militarily strongest nations.
The other child, who will someday turn into Hairy , meanwhile, is unnerved by all this and wants to stop playing. Since Hairy is just a normal child he is really not interested in Black Hat's realistic version of what a war really is.
In the title text it seems like Hairy interrupts Black Hat's last rhyme after twenty, and finishes with his own rhyme, with "Bunny" ending in the same sound if you pronounce twenty like "twunny" as in some parts of the world. So it goes like this:
Black Hat: Seventeen, eighteen, nineteen, twenty Hairy: Can't we just read Pat the Bunny?
Thus Hairy requests that they do something more appropriate for children, like reading a picture book - specifically, the "touch and feel" book for small children and babies known as Pat the Bunny . It isn't clear what Black Hat would have said if not interrupted, but if twenty was indeed pronounced so as to slant-rhyme with bunny, one possibility is, "I'll annex your entire country," (which could conceivably be followed by, "Twenty-one, twenty-two, twenty-three, twenty-four. You're not sovereign anymore.").
This is the second time a young Black Hat has been used. The first was in 1139: Rubber and Glue . Black Hat has continued to make Hairy uncomfortable even as an adult, for instance in 1210: I'm So Random .
[Two children are sitting on their knees between a toy truck to the left and five building blocks to the right; three square blocks are stacked in a precarious tower and to the right of the tower there is one more square block which has a rectangular block leaning on it. Both children have lots of hair but the child to the left has a black hat on, so they are possibly young versions of Black Hat and Hairy. They are sitting across from each other with one hand touching the other's hand. Their thumbs can be seen sticking up above their hands.] Black Hat: One, two, three, four, I declare a thumb war. Black Hat: Five, six, seven, eight, finger guns proliferate. Black Hat: Nine, ten, eleven, twelve, digits can't protect themselves. Black Hat: Thirteen, fourteen, fifteen, sixteen, thumb U.N. won't intervene. Hairy: I don't want to play with you anymore.


Tornado Safety Tips

Explanation:
The comic features a Public Service Announcement (PSA) poster, which generally contain public-interest messages aimed at raising awareness or steering behavior around a specific issue of concern, that in this case contains tips for tornado safety. Typically, a poster labeled "Tornado Safety Tips" would be filled with instructions for how humans can stay safe in the event of a tornado, such as "stay away from windows," "go to the lowest floor of your home," "if in the open, take shelter in a ditch," and so on, see these examples: Example 1 (with same title as comic), example 2 and example 3 .
Black Hat on the other hand, has flipped this on its head by publishing a poster that contains safety tips for the tornado itself and contains information for how tornadoes can stay safe, i.e., continue to exist; see the table of tips below. The joke is that just as, for example, a "climber safety" poster is directed at climbers, the "tornado safety" poster is directed at tornadoes.
It is thus in no way helpful for people who actually live in an area that experiences tornadoes or even for people that don't live in tornado-prone areas but want to be ready for their possible occurence [ citation needed ] . It is not possible to follow most of the guidelines [ citation needed ] , as they are intended for tornadoes. But the advice a human could follow would only take you towards places which can sustain tornadoes. Instead they should choose to use an app like the one in 937: TornadoGuard .
The title text simply adds more tornado advice for tornadoes, bringing up the common myth about tornadoes not crossing mountains, except from the tornado's perspective.
Although this is clearly not a tip for humans, the idea of tornado safety tip is yet another tips comic .
Tornadoes are a recurring subject on xkcd. The tornado in this comic is similar to the picture used in the Tornado version of 1037: Umwelt .
[Beneath a large caption there are two pictures above each other to the left and a bullet list with five points to the right of the pictures. The top picture shows a black tornado beneath a white cloud. It is destroying something on the ground. To the right of the debris is a house and to the left some trees. The picture below shows Black Hat from the waist and up.] Tornado Safety Tips Avoid low-lying cool air Keep your downdrafts and updrafts from mixing Seek out warm and humid surface air layers Don't let rain-cooled air choke off your circulation Avoid letting your supercell merge with a squall line


Old Days

Explanation:
This comic is showing a conversation between (young) Cueball and (old) Hairbun about computer programming in the past, specifically the compilers . Cueball, having a faint idea of just how difficult and byzantine programming was "in the old days", asks Hairbun to enlighten him on the specifics. Hairbun promptly seizes the opportunity to screw with his head. This later became a series when 2324: Old Days 2 was released more than 3 and a half years later. While her initial agreement that code needed to be compiled for multiple architectures is correct, Hairbun's claims rapidly grow ridiculous.
Hairbun tells Cueball a tall tale about how hard it was back in the old days , making it sound like some of the programming languages used today (C, C++) were written on punch cards and that you had to ship your code in the mail to a computer company ( IBM in this case) to compile your code, which would take from four to six weeks. If there was a simple error, you would have to ship it again for another compilation.
This is factually incorrect, but is plausible to those who do not have the knowledge or context to challenge it, similar to a Snipe hunt , or several other cultural myths told about things like the Tooth Fairy . It is clear from Cueball's final Wow that he falls for it. She then continues to explain more and more implausible so-called facts from the the olden days.
What she says is true in that it was tough and slow to program on punch cards, which were actually used for an extended period of time. However, there is very little in the rest of Hairbun's story that  accurate, except that it was a big deal when the floppy disk was invented. The comment about punching holes in floppy disks is true. However, the nature and purpose of the holes punched this way was dramatically different than in punch cards. 5.25" and 3.5" floppy disks had holes or notches in them to indicate the data capacity and it was common to punch additional holes into cheaper, lower capacity floppy disks to trick the computer into writing more data on them than specified by the manufacturer. With punchcards on the other hand, the holes themselves encoded the data so punching them was itself the act of programming. It is unclear if this was a coincidence, or intentionally included as a humorous aside to the readers who know the history as a misinterpreted truth in a sea of falsehoods.
In the title text, Hairbun continues her musings on the old compiler days, stating that there was a lot of drama in those days . Specifically she references Reflections on Trusting Trust a famous 1984 paper by UNIX co-creator Ken Thompson in which he described a way to hide a virtually undetectable backdoor in the UNIX login code via a second backdoor in the C compiler. Using the technique in his paper, it would be impossible to discover the hacked login by examining the official source code for either the login or the compiler itself.  Ken Thompson may have actually included this backdoor in early versions of UNIX, undiscovered. Ken Thompson's paper demonstrated that it was functionally impossible to prove that any piece of software was fully trustworthy.
Hairbun claims that one of the dramas she refers to was that people tried to force Ken Thompson to retire, so everyone could stop being so paranoid about compilers.  In reality, any coder who created the first version of a compiler (or a similar critical component) could inject a similar backdoor into software, so it would be false safety. Even if no one else had thought of this, then Thompson's paper was there for any future hacker to see. Though the problem was (claimed to be) solved in David A. Wheeler 's Ph.D dissertation " Fully Countering Trusting Trust through Diverse Double-Compiling (DDC) ".
[Cueball and Hairbun are standing together and Cueball is talking to her.] Cueball: What were things like in the old days? Cueball: I hear that you had to ... compile things for different processors? Hairbun: Yeah
[Same setting in a slimmer panel, now Hairbun is replying.] Hairbun: To compile your code, you had to mail it to IBM. Hairbun: It took 4-6 weeks.
[Close-up of Hairbun from the waist up.] Hairbun: Before garbage collection, data would pile up until the computer got full and you had to throw it away.
[Same setting as in the first panel with Hairbun gesturing toward Cueball raising one hand  palm up.] Hairbun: Early compilers could handle code fine, but comments had to be written in assembly.
[In a frame-less panel Hairbun is seen from the front, with both arms out to the side with both hands held palm up.] Hairbun: C could only be written on punch cards.You had to pick a compact font, or you'd only fit a few characters per card.
[Exactly the same setting as the first panel, but with Hairbun doing the talking.] Hairbun: C++ was big because it supported floppy disks. Hairbun: It still punched holes in them, but it was a start. Cueball: Wow.


I'm With Her

Explanation:
In this serious, no joke , comic released the day before the 2016 United States presidential election (which was more contentious than most, due in part to many people finding both candidates unusually distasteful), Randall urged his American viewership to vote, and showed his endorsement for Hillary Clinton , the Democratic nominee in the election. She was up against the Republican nominee Donald Trump , who ended up winning. For the sake of completeness, it should be mentioned that there were also nominees from other parties, including Green Party nominee Jill Stein , and Libertarian nominee Gary Johnson . Neither hoped to garner enough votes to become president, but there was a chance they could affect the result in some states (no third-party candidate has won a state since 1968 , and it did not occur this time either: the closest any came in 2016 was independent candidate Evan McMullin in Utah.)
It was the second time Randall referred to this election, the first being 1748: Future Archaeology three weeks before the election, but here it was just a wish to know the result using time travel (of course he did not learn the result back then…).
The "H" with an arrow was Clinton's campaign logo, and I'm with her an official slogan that was widely used by her supporters, hence the title. Randall then lists tips to help you cast your vote ( see table below ) suggesting a personal investment in the election. Clinton herself may be represented by Blondie sitting on top of the H looking out at the reader as the only of the 11 characters. The only type of joke in the comic is the chosen characters. Two with weapons flank the left and right side looking out ready to defend against Trump: Ponytail with an emp gun (that she also wielded in 322: Pix Plz for melting computers of persons who make snide remarks at women, clearly a reference to allegations of Donald Trump's sexual harassment of women in general and especially to his grab them by the pussy comment ) and Cueball with his sword (from 303: Compiling ). See more details in the character gallery below.
This is the first time Randall has used a comic to directly support a presidential campaign, although he did endorse Barack Obama in 2008 on his Blag . At that time, Randall wrote that he was troubled by Hillary Clinton's "basic lack of integrity", which is interesting considering he later endorsed her. He wrote later that it was very controversial when he endorsed Obama, but that it was not the most controversial comic he had published at that time. This comic might take that prize now, given that this was one of the most discussed elections up to its time.  This is particularly noteworthy outside the US—for example, some European leaders openly opposed Trump, while others supported him. There were also reports of Russian hackers attempting to influence the election.
Randall's support for Hillary Clinton may have been due in part to Donald Trump being a prominent climate change denier . Randall has published comics opposing climate change denial such as this: 1732: Earth Temperature Timeline , published less than two months before the election, as well as several other comics on climate change . Also Trump beating Clinton made Randall's regex that matches the last names of elected US presidents but not their opponents impossible to update.
All the information on the bottom half of the comic includes sites, numbers, info, etc., current as of 2016, that are intended to help US voters to vote, regardless of whom they vote for. Including this information can assist voters who don't understand the process, don't feel that it's worth it, or feel intimidated or threatened.  In general, these sites and numbers were likely included to help boost voter turnout.
The title text, "We can do this", refers to Randall's desire to unite Democratic voters and elect Hillary Clinton to the White House instead of Trump.  One can buy T-shirts with the famed " We Can Do It! " logo from the Rosie the Riveter wartime poster, but with Hillary Clinton in the famed position.  Both resemble the former president Barack Obama 's campaign slogan Yes We Can and German Chancellor Angela Merkel 's " Wir schaffen das " (We can do this) refrain during the Syrian War refugees influx the year earlier—like Clinton, Merkel was fighting against a populist nativist movement that wanted to close the country's borders.
Unfortunately for Randall, these efforts were in vain, as Donald Trump was elected on Tuesday, November 8. This result became a fact less than two weeks before the first ( 1761: Blame ) of several sad comics that all seemed related to the election of Donald Trump. Trump was never mentioned in these directly sad comics, and it took more than two years before his full name was finally used in xkcd in 2137: Text Entry in April 2019. Here it was remarked that the fact that Donald Trump was president was the weirdest thing of 2019.
The list of things that can help is all about getting people to vote.  While Randall is likely to have wanted to boost voter turnout regardless of political leanings, it's clear from his endorsement of Clinton that he believed increased turnout would have helped her win the race.  There is general evidence that certain more heavily Democratic-leaning demographics are less likely to vote, and in this election in particular, the various political issues that had been raised against Hillary (such as the FBI's public disclosures of its investigation into her use of a private email server) were shown to have reduced enthusiasm among Democrats.  But all these issues aside, both Republicans and Democrats alike agree on encouraging everyone to vote, and Randall is likely to have agreed with that sentiment as well.
Here is Randall's list of suggestions for how to help Hillary Clinton win the election:
The comic shows a gallery of 11 xkcd characters including all the main characters from xkcd (except Hairy ), which stand united behind Randall and Clinton despite their lack of agreement in many other comics.
Note that the two characters at either side of the comic wield weapons pointing out, defending the other nine. Those next to the characters with weapons are doing recreational things like kiting and admiring adorable squirrels, both of which are recurring subjects in xkcd.
[Inset: Eleven characters are drawn around a huge H with a rightwards arrow as the horizontal bar connecting the two vertical towers.  Ponytail stands on the left with a raygun looking leftwards. Behind her is Black Hat who looks at a girl that might be Danish or Megan (but with longer hair than Megan typically has). She is flying a kite above the first two characters. Behind her and looking up at the kite is White Hat. The H is right behind him, and on top of the left tower sits Blondie looking straight out at the reader with her legs dangling over the edge and her arms resting on her knees. On the arrow sits Megan leaning against the left tower, also dangling her legs over the edge and arms resting on her knees. Cueball stands to her right by the right tower. On top of the right tower sits Hairbun with glasses looking straight right with her legs dangling over the edge one arm resting on a knee and leaning back on the other arm. On the right side of the H is an adult version of Science Girl holding a hand out towards the squirrel which Beret Guy is holding out in both arms towards her. Another Cueball stands on an office chair on the right brandishing a sword looking rightwards. He keeps his balance by holding his other arm out behind him. Caption] I'm with her.
[Centred] How to help Vote―iwillvote.com Get a ride to the polls―drive2vote.org If you're having problems voting―866-OUR-VOTE Experimental social turnout project―civicinnovation.com App Store: VoteWithMe Reminder: If you're in line when the polls close, they have to let you vote.


November 2016

Explanation:
This is yet another comic designed to make people feel old , following soon after the last one 1745: Record Scratch . Not so long ago a comic with the very title of the largest bold letters in the caption above the panel was released: 1686: Feel Old . The next comic about feeling old, was released 11 months later, with a similar title, which is special in itself, 1898: October 2017 see more on both title and this follow up comic in the trivia section below.
Specifically this comic contains The November 2016 Guide to making people feel old . (The unusual title for the comic indicates that it only works during this month). It lists ages between 16 and 41 and links each age to one or more events that happened approximately half that age ago, so 8 years ago for the 16 years old and 20 years ago for the 40 years old etc, which means that a person of that age would have had the mentioned thing in their life for the majority of their life. And then it explains that to make a person of a given [age] feel old, look up the [thing] (or things) connected to it, and say:
"Did you know [thing] has been around for the majority of your life?"
As an example the age 21 can be used, as it list both the Xbox 360 as well as this comic, xkcd itself. The two possible sentences would then be:
"Did you know that the Xbox 360 has been around for the majority of your life?" "Did you know that xkcd has been around for the majority of your life?"
This matches earlier attempts to make people feel old by mentioning how long ago it was that, for instance, a movie comes out as was the case in 891: Movie Ages . (But on this exact day when the comic was released there might have many people who did already feel old and tired - see trivia ). When an event seems to have occurred recently to you, like seeing a movie when you were twenty (with Toy Story ) and then suddenly realizing that this was 21 years ago, you will very likely feel old. Since humans' perception of time is not related to how much time has actually passed but rather to important memories, then memories like seeing the first feature-length fully computer-animated movie ( Toy Story ) makes a big impression and may stay vivid in peoples' memories. When they then, after hearing the sentence from this comic, realize that more than half their life has passed since that event, they realize how much time has passed and that makes them feel old.
This is why it affects a 20-year-old to hear that Twitter is ten years old, where this will not have the same impact on a 16-year-old, since they were so young when it came out that they probably feel like it has been around for ever, and you do not feel old by hearing, for instance, something like that the TV was invented before you were born. It thus makes sense to pick something that happened almost midway through a person's life, because they then realize they are now double as old as when they first heard of Twitter. Of course also many ten years old would not have been active on Twitter when it was released, so it may not have that big an impact on those 20 years old today.
The joke at the end is that people over 41 don't need anything to make them feel old, because they already feel old. He thus teases people above 41 years old by claiming they are old, although many people (above 40) would claim you are not old before you retire. This trick was also used to cap the above mentioned 891: Movie Ages to 35 years old, stating anyone as older was already old. But that comic was also released five years ago, and now Randall is himself closing in on 35 at 32 years at the time of this comics release. So he pushed the limit 6 years further, probably for this reason. Now he no longer thinks people at 36 are too old to try to make them feel old.  It may be a coincidence, but still interesting, that he stopped the list just before 42, a number Randall has referred to many times in relation to it being the " Answer to the Ultimate Question of Life, the Universe, and Everything " in the Hitchhiker's Guide to the Galaxy .
The title text points out that the same chart can be used for the same person once they are twice as old. So it urges the user to note down the age of the person it was used on, and then wait until their age reaches double that. So for a 16-year-old that would only be 16 more years until they are 32, but for a 41-year-old it would have to wait until they are 82 years old. When showing them this chart, they will realize that this has existed for half of their life and again have the same type of "feeling old" that this comic is supposed to instigate today.(It will work better if they still remember the joke made on them those many years ago)...
[Caption above the panel:] The November 2016 Guide to making people feel old [A chart with a list of items to be put into the two first lines above the chart. First there are a line using the first column, then there are two lines using the second column. Below those lines are the two columns with underlined captions above. Between the columns are a long line connecting the two.] If they're [age], you say: "Did you know [thing] has been around for the majority of your life?" Age Thing 16 Grand Theft Auto IV 17 Rickrolling 18 Aqua Teen Hunger Force Colon Movie Film for Theaters 19 The Nintendo Wii 20 Twitter 21 The Xbox 360, xkcd 22 Chuck Norris Facts 23 Opportunity's Mars Exploration 24 Facebook 25 Gmail, Pirates of the Caribbean 26 In da Club 27 Firefly 28 The War in Afghanistan 29 The iPod 30 Shrek , Wikipedia 31 Those X-Men movies 32 The Sims 33 Autotuned hit songs
34 The Star Wars prequels 35 The Matrix 36 Pokémon Red&Blue 37 Netflix, Harry Potter , Google 38 Deep Blue's Victory 39 Tupac's Death 40 The last Calvin and Hobbes strip 41 Toy Story >41 [Don't worry, they've got this covered]


Astrophysics

Explanation:
In physics, the theory of gravity produced by general relativity combined with dark matter are our current best model for explaining the behavior of gravity and galaxies.  The evidence supporting this model is extensive.  General relativity accurately predicts the orbit of planets, even precise details like the precession of Mercury which Newtonian gravity couldn't fully explain.  Dark matter, in turn, explains behaviors of galaxies such as their rotation rates that were not correctly predicted with general relativity alone.  Most astrophysicists believe dark matter exists, either in the form of an unknown type of star that is too dim to see , or an undiscovered subatomic particle .
However, because the concept of dark matter posits something so pervasive yet unknown and so far undetected, it can be difficult to accept, since typically inability to detect something tends to mean non-existence of that thing. One might be reminded of Aether , a similar theory that an undetectable substance exists in space to allow light and gravity to travel, although unlike dark matter that has been debunked. Thus, it is common to hear objections to dark matter, with a popular alternative idea being that dark matter can be explained away by a modified theory of gravity.
One such alternative theory which gets proposed regularly is modified Newtonian dynamics (MOND). In MOND, gravity doesn't simply follow the inverse square law but has more complicated behavior. Usually, the extra behavior is either to say that gravitational force can be affected by the acceleration of the particle, or that it goes from inverse-square to just inverse at large distances. It can be appealing because it's relatively simple and seemingly more logical — it just changes our understanding of Newton's law of gravitation, rather than requiring entirely new forms of matter or unknown stars to exist — and because it has some nice side-effects, such as explaining why there seems to be a limit on the density of galaxies.  Unfortunately, physicists have explored this avenue and cannot reconcile it with all existing data. One famous counterexample is the Bullet Cluster , where two colliding galaxy clusters are ripping through each other.  The mass distribution within the cluster can be inferred through gravitational lensing, and appears to show dark matter and ordinary matter being separated to a certain extent which cannot be explained with MOND.  Another counterexample is MOND's incompatibility with observations of the motion of galaxies in galaxy clusters. More generally, MOND isn't compatible with general relativity — which has a huge amount of experimental data in its favour — and a MOND-compatible general relativity would be very complicated and ugly.
This comic illustrates physicists' exasperation for people who constantly try to challenge the existence of dark matter without considering all the evidence and theoretical foundation that support it.  Apparently members of this department are so tired of hearing the same old ideas being repeated to them, that they have adopted a motto and even erected a sign in an attempt to clear the dissuation.  The specific impetus for this comic may be the press coverage around this publication by Erik Verlinde (see popular description of the paper here ). It was released online three days before the release of this comic and got a lot of coverage exclaiming "this will prove Einstein wrong".  While Verlinde's work on entropic gravity is a serious theory derived from thermodynamics and quantum information theory , it is important to keep in mind that it's just a pre-print and hasn't been peer-reviewed or experimentally verified yet. Verlinde's theory also doesn't match all available data - it disagrees with experimental results showing how particles interact with gravity .  Thus, it is still a far cry from being a contender for replacing dark matter.
The title text alludes to a similar issue faced by the Department of Neuroscience from popular misconceptions of Mirror neurons .  Mirror neurons are brain cells which trigger when watching someone else do something. Experiments claim to have found mirror neurons in humans and apes, and there are theories that make mirror neurons the foundation of learning, empathy, language and consciousness itself. However, the evidence for mirror neurons is still patchy , and even if they exist, it's very simplistic to try to attribute so much of human behavior to a single type of relatively simple cell. In light of this, the motto of the neuroscientists at the department rightfully reflect their frustration. Flipping tables is a common depiction for expressing extreme outrage. It is used here also as a pun because mirrors flip the image in front of them.
Another story of similar press coverage questioning the current established scientific theory was also mentioned two days before the release of this comic, on the YouTube channel Space Time from PBS Digital Studios in their video titled Did Dark Energy Just Disappear? .  This one was regarding the paper Marginal evidence for cosmic acceleration from Type Ia supernovae . The video concluded that dark energy is still the best explanation. Note this is about the existence of dark energy rather than dark matter. The two are very distinct concepts.
Science papers with results that supposedly disprove solidly founded theories have been the subject before in 955: Neutrinos .
[A sign on two posts, in the grass in front of a building with windows and double doors, a window on each door, and bars facing outwards. There is a cement walk leading to the doors. On the sign is the text:] Department of Astrophysics Motto: Yes, everybody has already had the idea, "Maybe there's no dark matter—Gravity just works differently on large scales!" It sounds good but doesn't really fit the data.


British Map

Explanation:
This comic is a joke similar to "How Americans see the world" showing how the average American has opinions on the world, often including jokes such as a lack of Africa , etc. This has been used before in 850: World According to Americans . The map also plays with the joke by noting it has been labeled by a specific American rather than "Americans".
Many areas of the UK are most familiar to foreigners thanks to their depiction in various fantasy novels and TV series. This map labels some of these, as well as including many silly names that simply sound like real British towns to an American ear. A protractor is shown off the coast of the Mull of Kintyre in reference to the " Mull of Kintyre test " - according to urban legend, the angle of the Mull defines the maximum allowed erectness for a man on films and home video releases in the UK.
Randall previously posted a map of Great Britain on his blog as part of the promotion for his book What If? . This map is from a very similar position and appears to have been traced from the same source, although there are some slight differences. Both maps include a sketch of Lake Windermere with boats on it, and both have the locations of London, Oxford and Cambridge labeled (the blog map also shows Edinburgh and Bristol - in this comic, these are labelled Eavestroughs and Minas Tirith). Both also contain references to Stonehenge and Watership Down .
Note that in British English, the correct spelling of “labeled” is ‘labelled’.
The title text plays around with the concept of the compass directions and how numerous regions (such as South "Sussex" and West "Wessex") incorporate such literal names in their description. Randall is creating similar sounding names which are nonsense-ish ("Norsussex" would be the region of the Northern-Southern Saxons), and placing them in relation to each other in ways which would be geographically implausible, similar to this old joke about Boston . However, in Germany there exists the region called Westphalia ( Westfalen ), and the eastern part of it is often referred to as East-Westphalia ( Ostwestfalen ), which sounds somewhat ridiculous. Part of the joke in the title text could be the fact that while three of the locations are fictional, Middlesex does actually exist.
[A black-and-white map of Great Britain. The detail on the map is minimal, showing mainly the outlines of the land, upward-pointing angles representing mountains, and points representing cities. The only other features are a small drawing of a protractor south of one peninsula, and a lake with two small sailboats on the west side of the largest landmass. The caption in the upper-right states in large letters "A BRITISH MAP," then in smaller letters underneath, "LABELED BY AN AMERICAN." Most of the map's area is covered by labels for various features, which are listed below.]


TV Problems

Explanation:
In this comic, Cueball has broken his computer's software so much that he is unable to "turn on the news" as requested by White Hat . Since his computer is not working at all, he is using the next best thing to download a fix: his smartphone, via a CD . This is probably one of two things:
He later states that even that first step of mending won't be enough to display the news, as his computer's state is so bad that being able to send information to the TV screen is just the first step of debugging. In the last panel, he tells White Hat that his computer science degree just helps him understand how he ended up with such a terrible situation, but did not give him enough foresight to prevent the most unexpected issues. The title text clarifies this statement with a similar problem- when things start to go horribly wrong while falling from a plane, certified skydiving instructors will be able to better understand why and how bad the situation is, but won't be able to do anything if their usual tools have failed them. Besides, while they are less likely to make a fatal mistake on a given flight and fall, they are more likely to make one in their life, because of the far greater number of attempts. This is especially true considering most people never attempt a jump in their lives, giving them absolutely zero probability of dying in a skydiving accident. This also resembles 795: Conditional Risk : the more informed a person is, the more likely this person is to suffer from the issue they know about.
Computers breaking in unexpected ways, and somewhat weird solutions to computer problems seems to be a thing with Cueball - and probably Randall as well. At that point, you might assume he probably enjoys it. In 1586: Keyboard Problems , he also had a problem involving both software and hardware. 1739: Fixing Problems could very well apply to this comic; Cueball may have ended with this situation while trying to correct a simple problem (eg: channels in the wrong order), and just made the situation worse every step of the way. In 456: Cautionary , he teaches his cousin about breaking fixing a computer.
In this instance Cueball has his single tasking phone busy while he downloads to it and cannot interrupt what he's doing just to use the phone as a remote for the TV, although it appears more that the TV is one of the things he is trying to fix.
[Cueball is sitting by his TV, holding his phone, when White Hat walks in.] White Hat: Hey, turn on the news. Cueball (Sitting on the floor in front of a computer holding a cell phone): Can't. Downloading a CD onto my phone.
White Hat (off-screen): Why? Cueball: So I can use it to fix my computer's operating system enough that I can teach it to talk to my TV screen.
White Hat: But then you'll be able to watch the news? Cueball: (off-screen): No.
White Hat: Don't you have a computer science degree? Cueball: That just means I understand how everything went so wrong.


Blame

Explanation:
Cueball is blaming his "friends on Facebook " for "bad things [that] are happening".
People often rant on social media sites (like Facebook) about various things which are blamed on certain people (or sometimes usually everyone), but the person doing the ranting never thinks that the problem might be with themselves.
While there could be possible reasons for bad events (for example if the bad event was nobody wishing him a happy birthday or someone posting compromising pictures), his friends would not be a likely source for bad events extending beyond a personal or local scope. Most people have a few hundred (or thousand) "friends" on Facebook, most of whom do not have enough influence to cause bad events on a national or global level. [ citation needed ]
The title text refers to people venting. The humorous assumption here is that one will feel better after doing so. While some amount of venting might help to relieve stress caused by bad events, alienating people you know by blaming them for bad events usually causes more stress in the long run.
[Cueball stands.] Cueball (thinking): I feel sad. Cueball (thinking): Bad things are happening.
[Cueball still stands.] Cueball (thinking): They must be someone's fault. Cueball (thinking): But whose?
[Cueball makes several thinking poses before a light bulb appears over his head.]
[Close-up of Cueball's head.] Cueball (thinking): My friends on Facebook.


Moving Boxes

Explanation:
Randall talks about moving boxes and not labeling them until he forgets what's in them. Since he doesn't know what's in them, he writes silly things on the boxes as a joke. Some things are unusual/unlikely (e.g. sand, hydrants, peat) and some are abstract/impossible (e.g. elves, taupe, dark matter). Several of the categories overlap confusingly; for instance, "sand" and "silt" and "dark matter" are all generally considered as "particles"; "membranes", "edges", and "shawls" are all kinds of "manifolds"; "hooves" are part of "bison"; "fog" contains "water"; and "triangles" consist of three "edges". Another way to interpret this comic is that Randall actually has these items (or at least some of them) in the boxes and has simply forgotten which boxes contain what.
According to the title text, when Randall remembers that he is calling movers, he frantically scribbles "Normal House Stuff" on all the boxes. He says this makes the situation worse, possibly because the movers see the scribble and become suspicious. Alternatively, labeling every box with the exact same phrase will make it even harder to figure out what they contain and where they should go in the new dwelling.
[A bunch of cardboard boxes stacked up, each labeled]
Contents: Grids Bison Checkerboards Fog Contents: Beacons Elves Sand Contents: Hemoglobin Contents: Water Hooves Contents: Shorebirds Contents: Oil Vectors Silt Contents: Membranes Shards Contents: Shawls Glucose Kits Hydrants Particles Knots Contents: Graphite Taupe Contents: Field Lines Contents: Traps Contents: Edges Tribes Dough Contents: Dark Matter Contents: Manifolds Contents: Triangles Peat Crowns Contents: Scrolls
[Caption below the panel:] I always forget to label my moving boxes until they're sealed up and I've forgotten what's in them.


Catcalling

Explanation:
" Catcalling " refers to the act of whistling or shouting  to express sexual interest in a person, and often constitutes harassment. Annoyed by this practice, Megan alters the Universe Control Console to create a setting in which catcalling actually attracts cats (as the name implies), thus resulting in the catcaller being harassed by the overwhelming feline presence, instead of the other way around, likely in an attempt to discourage the act.
When read without the title text, it could be assumed that Megan is trying not to punish catcallers, but to turn catcalling into a positive thing, since after the change is made catcalling will no longer offend women and instead attract the attention of cats, an animal many people on the internet find cute. [ citation needed ] It is only with the clarifying information in the title text that it becomes clear that Megan is trying to punish catcalling, thus changing the joke.
It is interesting to note that changing what women find insulting/harassment would involve fundamentally changing their psychology on some level. How exactly the Universal Control Console will make them immune to this specific behavior is unclear. The Universal Control Console is an intentionally ambiguous device, but based on how Megan and Ponytail used it in 1620: Christmas Settings , it can be implied to change people's memories of what reality was like before a change, so using the catcalling example, it might make everyone in the universe forget what catcalling initially was, thus removing the insult of even trying to do it in the first place.
The "Universe Control Console" was introduced in 1620: Christmas Settings as the "Universe Control Panel", where it was used to control aspects of reality related to Christmas.  Based on the name, it is presumed all aspects of reality could be altered using this fictitious device. The pointer arrow and menu options shown above Megan appear to depict aspects of the user interface that Megan is seeing. In 2240: Timeline of the Universe someone hit the inflation switch starting the inflation again. And then someone stopped this by hitting the emergency stop. These must also be on the Universe Control Panel.
The Console appears to have been modified/upgraded since its last appearance and features fewer controls while gaining a joystick in this incarnation. It also appears that Megan has learned to operate the console better since first encountering it. ( Ponytail , who first demonstrated the console to Megan, could be the offscreen voice in this comic.)
Furthermore, the title text suggests that catcalling now attracts all cats within two miles for an entire year. The prospect of being piled in cats for a year would discourage people from catcalling by a large amount. [ citation needed ] 1156: Conditioning also persuades people to change behavior related to wildlife.
The redefining of terms related to sexual harassment as more innocent things has also been discussed in 1178: Pickup Artists .
Also, the cursor on the console is left-handed for some reason.
Offscreen: Hey! Are you messing with the Universe Control Console!?
Megan: [standing at a control panel with a small lever and what appears to be a display] It's cool. Just gotta fix one thing.
[Megan still at the control panel; now a mouse pointer appears]
[Megan still at the control panel; "Catcalling" appears written at the top of the panel above a dropdown menu that says "Harasses women"; the pointer is hovering over the arrow]
[Megan still at the control panel; The dropdown menu is expanded to show two elements: "Harasses women" and "Attracts cats". The pointer is hovering over "Attracts cats", which is highlighted]


XKCDE

Explanation:
Randall has created a theoretical software environment named XKCDE (a portmanteau on xkcd and CDE (Collaborative Development Environment)), which relies on the user creating a series of nested virtual machines inside each other (creating sort of a digital version of the Droste effect ), which would likely cause extreme strain on the resources of the machine running it. This strain is explained in 676: Abstraction , at least for the normal case.
"Virtual Machines" are software which pretend to be PC hardware so that a "guest" operating system can run inside of them, under a "host" operating system. Nesting VMs is the process of making a guest also be a host to yet another guest. Generally this is considered wasteful of resources, especially beyond one or two layers deep, and is not done except in a test lab for very specific purposes.
"Containers" are a lighter form of PC abstraction. Instead of emulating the entire physical hardware, they only emulate the software stack sitting on top of the kernel. A containerisation tool will have its own standard library, software-stack and installed programs, but delegates all system calls to the host kernel.
This is more efficient because no hardware needs to be emulated, but the disadvantage is reduced isolation between host and guest. A misbehaving guest can induce kernel crashes that take the host with them.
The most well-known example of container software is Docker .
Randall derives humour from repeating the nesting ad absurdum in a never-ending fractal of nested VMs, thus trapping the follower of the instruction forever, in a form of Nerd Sniping : Any external observer, such as your boss, who sees you doing this is likely to fire you for wasting company time (An outcome which is undesirable, though still better than being hit by a truck [ citation needed ] ).
A software environment which disables both the machine it runs on and the user that runs it could be thought of as a useless machine.
The title-text is a joke on the words root and leaf as used in abstract data structures, drawing an analogy of cutting down a tree (unplugging the root machine) scattering leaves (the nested VMs).
A subtle pun is hidden in 'spinning': several tree species use spinning leaves to scatter their seeds. The autorotation due to the special shape of the leaves helps the seeds travel farther on the wind from their parent tree.  Randall mixes this meaning of 'spinning' with the act of "spinning up a VM", the colloquial phrasing for starting up a new instance of a guest virtual machine.
As a seed grows into a new tree where it lands, so apparently do the scattered VMs spin up new instances of themselves wherever they land.
In this case, a literal interpretation would be that turning off the computer the VMs are running on would make all the VMs without any VMs running in them propagate themselves through a network and install themselves on other computers, which at the end of the day would be a very inefficient method of creating a virus.
In 'normal' software development, spinning up a (single, non-nested) VM is a practice to ensure that the development environment is identical between developers, thus minimising hard-to-reproduce bugs due to local machine differences, such as unmatching library versions , locale settings or additional installed or missing software .
The single VM image is shared between all developers, who each spin up their own instance on their personal workstation.
In such cases, spinning up the VM is the first step in bringing up a local development environment, after which additional steps will usually instruct which programs to open, which configuration settings to change, etc.
Someone got 4 levels deep with this.
Installing the xkcd development environment
[Inside a frame three instructions are shown:] 1. Spin up a VM 2. Spin up a VM inside that VM 3. Continue spinning up nested VMs and containers until you get fired


Baby Post

Explanation:
In this comic, Cueball is questioned about a series of posts made to his Facebook account. He explains the posts as the result of leaving his daughter (a baby, according to the title) unattended with his tablet. This is very common for parents with small children in modern times. Children tend to be fascinated with touchscreen devices, which include many entertainment options for small children (such as the mentioned " Wheels on the Bus " video). Infants also tend to experiment with such devices, and frequently open apps, post links, and make calls without intending to. [ citation needed ] This explains the first two panels: sharing the same video six times could be the result of the child repeatedly hitting the same area of the screen (such as a "share" link), and the gibberish text "FHFF,,,M,,,," could be due to the child randomly tapping on the screen, all without knowing what she was doing.
The joke begins when Cueball discovers an apparent pattern in the new posts, starting with a map of hardware stores and culminating in blueprints for the Tower of London . These subjects, if they were chosen consciously by an adult, would strongly suggest the poster was planning a heist to steal the Crown Jewels , which have a reputation, based in part on several movies (for example, Minions ), for being overly complicated to steal. It is very unlikely for a baby to be capable of designing and carrying out such a plan, [ citation needed ] but it is also unlikely for these specific links to be posted all by accident.  Cueball seems genuinely perplexed by the links (and presumably wouldn't have posted them if he were planning the crime himself), so the reader is left wondering what could have caused these posts, and whether Cueball and/or his daughter might know more than they let on.  Cueball's suggestion of "keeping an eye" on his daughter suggests he is seriously considering the possibility that she might be an evil genius.
The title text continues the joke by notifying Cueball that his flight to London is leaving soon, and an Uber driver is coming to pick him up. Since his daughter was using the tablet and he is surprised by the messages, this suggests she is in fact the mastermind who has already started executing her plan.  Either she is making the journey herself (and Cueball is only receiving notifications because he has the same accounts linked to his phone), Cueball is being roped into the crime, or his daughter is deliberately making it look like he intends to steal the Crown Jewels in order to get him into trouble.
[Ponytail is looking at her phone while talking to Cueball.] Ponytail: Why did you post a The Wheels on the Bus Youtube video to Facebook six times? Cueball: Haha, whoops! My daughter was watching the tablet and must have hit something.
[Cueball is talking to someone on the phone while pushing a shopping cart with a few items in it.] Phone: Hey, did you mean to post "FHFF,,,M,,,," and a link to a map of hardware stores? Cueball: I should really look up how to lock the screen.
[White Hat is holding his phone while walking with Cueball.] White Hat: You just posted videos on metal-working, zip lines, and camouflage. Cueball: Uhh...
[Ponytail is looking at her phone while talking to Cueball.] Ponytail: Um, you posted blueprints of the Crown Jewel rooms in the Tower of London. Cueball: Maybe we should be keeping more of an eye on her.


Apple Spectrum

Explanation:
The comic shows a spectrum of different types of apples, with Red Delicious towards the bad end of the spectrum, and Honeycrisp towards the good end of the spectrum. Although most spectra are only one-dimensional, Granny Smith is on some side branch, implying that the taste is so different from the other two that it deserves its own category. (Granny Smith apples have a distinctively tart, or sour, flavor with a subtle sweetness, and is commonly used for cooking, as opposed to the other mentioned varieties that are quite sweet and primarily eaten raw.) Randall has previously shown his disdain for Red Delicious apples in footnote 1 in this what if ; he also ranked green apples as tastier than red apples in 388: Fuck Grapefruit .  The labeling of Red Delicious as "bad" compared to apples in general is perhaps unwarrantedly uncharitable; most apple trees produce fruit so bad that it is considered unfit for any purpose but fermentation.  On the rare occasions that a tree naturally produces palatable apples, it is grafted onto other trees so that they will produce more of its apples instead of their own--all Granny Smiths are genetically identical. For a long time, though, in the US apples were mainly divided into three sorts. In case of the Red Delicious apples the colour, not the taste was deemed most important to the buyers which (along with the genetic variability of Red Delicious) lead to many Red Delicious apples breeds that looked great, but actually tasted bad leading to a big restructuration of the apple market.
In the title text, Randall observes a common type of hypothetical question designed as a creative way to inquire about a person's preferences: If he were on a desert island with an unlimited access to something they like -- in this case, unlimited supply of any one type of apple -- what would he choose? However, Randall gives an unorthodox and unexpected answer to the typically playful hypothetical by taking it literally and questioning how such a situation would occur. How did he get stuck on the island, and how did he get a literally unlimited supply of apples? In reality, a desert island is unlikely to have an unlimited supply of any food [ citation needed ] , let alone apples.
[A mapping, showing types of apples. Each apple is in a bubble]