Time Travel Thesis

Explanation:
Cueball has apparently been reading about time travel . He tells Megan about this, and Megan excitedly remarks that she did her college thesis on time travel which basically means that she is supposed to know a lot more about time travel than a guy who has just been "reading" about it.
Cueball, however, continues to ask her if she knows basic facts about time travel (like closed timelike curves , wormholes and exotic matter ), like he is investigating if he has discovered facets about it that she would have overlooked while writing a thesis about it. Megan keeps trying to say that since she wrote a Time Travel Thesis , (hence the title of the comic), she already knows all of this and much, much more, and she is obviously getting frustrated by Cueball's attempts to impress her with his "knowledge".
At this point Megan's future-self arrives with a Bzzzzt , having used time travel to arrive at this exact moment in time. It seem she has continued her research and has successfully managed to make a time machine.
The reason she arrives is only to tell her younger self that this conversation with Cueball doesn't go anywhere and isn't important, and so present-Megan can leave and not waste her time anymore. Up till then, Megan was presumably reluctant to break off a conversation on the topic of time travel, since the conversation could potentially have improved, or perhaps because he at least had read about time travel which is a subject she would have a clear interest in since she wrote a thesis on it. But once the conversation began to run off track, it came as a relief to know that she could quit without the risk of missing out on anything important. Also, since Megan took the effort to time travel back to this exact moment, that must mean the conversation was so boring and uneventful she kept regretting having this conversation even far into the future to the point where she remembers it as one of the moments that need to be changed with her acquired time travel abilities.
And then she just walks away with her future-self leaving Cueball hanging in the last panel, having invented a completely new way to get out of useless/boring conversations.
Alternatively, future-Megan just makes an excuse to haul present-Megan off in order to prevent the latter from disclosing some details of time travel science to Cueball, which could have unintended consequences. However, using very advanced technology, or even violating physics law, for very mundane ends is very common in xkcd, so using time travel to prevent useless conversation is not surprising from Megan.
In either case, future-Megan finished this conversation before inventing time travel, and thus knows this conversation's outcome. So by coming back, she now changes her own (and Cueball's) future. Of course the general implications of being able to travel like this are enormous, and the paradoxes arising from such a possibility are endless, the most pressing (at the moment) being the grandfather paradox , where a time traveler creates circumstances that negate their existence (such as killing their own grandfather), in this case, Older Megan going back in time to stop Younger Megan from finishing this conversation, who will eventually become Older Megan but with no reason to go back to tell Younger Megan to stop this boring conversation. It is worth noting, however, that the comic does not inherently cause a paradox: so long as the Megan who didn't finish the conversation stills travels back in time with the knowledge that the conversation needed to be stopped and still saves her younger self from wasting her time, a time loop can be logically sustained. (It is also worth noting that a "Mobius" time loop is also perfectly possible, the grandfather paradox isn't a paradox if quantum entanglement is taken into account - something Megan would no doubt know)
It is possible that Randall may have had some conversations like this, where after having spent a lot of time getting nothing out of it himself, would have wished his future self had come back to tell him to just leave the conversation now.
In the title text present-Megan asks future-Megan about her futuristic googles and what they are for, presumably assuming they are needed for the time travel (maybe it is the backpack?). People from the future wearing weird clothing, often involving eyewear of some sort is a trope in Science-Fiction. Movies like Back to the Future Part II which tried to predict the fashion of 2015 back in 1989 didn't get it right, so this might be a commentary on those movies. However it turns out it's just some old and broken Google Glass . The only reason future Megan wears these is that she attended a party at the club that had a 2010's night theme. The fact that the Google Glass is broken and from 2010 alludes to Randall believing that the project was a fad that and that it will never pan out, even in the future. Indeed that seems to be the case. It seems generally that Randall is no fan of Google Glass, which was also shown earlier in 1251: Anti-Glass and later again in 1304: Glass Trolling . Google Glass has become a recurring theme in xkcd.
This is an indication of how far from the future she has traveled, as Google Glass was first released in the 2010s. It is not clear whether she is wearing Google Glass because it became popular in the 2010s or because it was an esoteric piece of hardware that people would readily associate with the 2010s. Also a 90s party may be thrown today, but not a 2000s party. So it is safe to assume that Megan is at least from the 2030s. Also people attending retro dress-up parties frequently make mistakes and do not dress up exactly in-style, creating some anachronisms, especially if they dress up like they did many years ago.
[Cueball is facing Megan, talking to her.] Cueball: I've been reading about time travel. Megan: Cool! I did my thesis on time travel!
[Cueball is now gesturing toward Megan. An electrical charge of some sort is shown occurring outside the panel in the bottom right corner behind Megan.] Cueball: Nice! So you know about closed timelike curves? Megan: Yup. Thesis. Cueball: Apparently wormholes can use exotic matter to– Megan: I know. Like I said– Charge: Bzzzt!
[Megan has turned away from Cueball to the right. Megan from the future, wearing sunglasses, a headset and a machine strapped to her back has entered the frame from the right where the charge appeared.] Future-Megan: You can skip this conversation. It doesn't turn out to be important. Megan: Oh, thank God.
[Cueball is standing alone, the two Megans have left the panel.]


Pyramid Honey

Explanation:
Bee honey is a food item with natural antimicrobial properties. It can remain unspoiled for a person's entire lifetime, making it practically nonperishable for ordinary consumers. It is frequently claimed that archaeologists have found jars of honey that have been well-preserved for thousands of years in ancient tombs, often those found in Egyptian pyramids , hence the title Pyramid Honey . The claims are generally assertions that may point to other similar assertions as supporting evidence but do not provide specific details, such as the identity of the actual tombs where such jars have been found, or the names of the archaeologists who have affirmed finding such jars. Repeated encounters with the assertion lead some people to claim that honey's shelf life is "infinite", which is a much stronger claim which would not necessarily be supported by the assertion even assuming it is true.
In the comic, Cueball tells Megan about an article in Smithsonian Magazine (presumably this one ) that claims honey has an infinite shelf life. The article links to a book that makes the assertion of such findings but does not provide factual support of the findings. Megan thinks the source for this article, and others that covered the subject, is wrong and wants to refute them all. She tells Cueball Believe it or not which Black Hat hears and he immediately states that he believes her, and is convinced without hearing any arguments from Megan. He then decides to begin a Facebook page so he can tell the Internet without giving Megan a chance to explain any further.
"A hill to die on" is a phrase from Ernest Hemingway's 1940 novel " For Whom the Bell Tolls ", about an American who volunteers in the 1936-1939 Spanish Civil War to fight fascism , who ends up wounded and alone, about to ambush the enemy to give his comrades a chance to escape; "a weird hill to die on" would thus mean a weird cause, if not a just one, to fight for to the bitter end. This expression is also the subject of 2247: Weird Hill . Black Hat asserts that he needs such a cause because the "real" weird hills are too far from his house, humorously implying he would be equally satisfied with a literal weird hill.
Black Hat's actions are clearly premature since he has not heard any evidence to back up the claim and does not understand the nuances of Megan's position. Cueball states that it could have gone better, whereas Megan seems to be resigned to it, perhaps as it notionally supports her (aborted) argument and it's at least a short-term 'win' that she won't fuss over the details of.
Presumably, the best Black Hat can do would be to parrot what he has heard from Megan, without any understanding or critical thinking on his part. Due to his lack of understanding, he may even interject his own ideas (ones Megan never believed nor stated) into his posts. These are all consistent with him calling himself "pyramid honey truther". The word truther refers to people who reject established facts and instead choose to believe in conspiracies, like people who claim the moon landings never happened , or believe the US government is behind the 9/11 attacks . While a few conspiracy theories turn out to be true, most are easily proved to be fake, but this does not stop people from believing in them anyway, just like the two mentioned here, which are not easily dismissed by believers. This turns Megan, who likely has a reasonable and well-justified position, unwillingly into the source of conspiracy theories.
Alternatively, he only does this to troll Megan (and Cueball), and everyone else that reads his Facebook page, just because he knows they will get annoyed. And also to state that this is an unimportant subject (a weird hill to die on) to make such a fuss over. No one would wish to eat that honey, anyway, having been abandoned to time for that long. He may see this as a completely uninteresting subject and thus makes fun of Megan with his statements. This would also be more in line with his usual behavior.
It is also possible that Black Hat is simply mocking conspiracy theorists' obsessions with factually incorrect ideas, comparably to what may be the case in Secretary: Part 3 .
The title text refers to the Eye of Providence , a symbol of an eye at the top of a pyramid, found on US currency and often associated with conspiracy theories of the Illuminati . Black Hat again refers to the pyramid honey found under the pyramids and calls it a conspiracy that goes all the way to the top . This usually means that the politicians (or the government agencies) ruling the country know about it, but keep it a secret from the public. But in this case, he mixes up terms and says it goes to the top of the pyramid (from the bottom), to where the giant eye is. As promised he also writes four words in all capital letters, shouting out the TRUTH!
This comic is likely a satire of the stereotypical internet mindset and plays up the frequent confusion between legitimate scientific skepticism, where unsupported claims are rejected, and conspiracy-theory faux-skepticism, where legitimate evidence is rejected because it does not support a specific viewpoint.
[Cueball and Megan are talking.] Cueball: Apparently honey has an infinite shelf life. They just found jars of it in the pyramids, still good. Megan: You know, I've heard that, and I don't think it's true.
[Black hat enters.] Cueball: Really? Smithsonian magazine confirmed it. Megan: Believe it or not, I think their source is wrong. Black Hat: I believe you.
[Megan has turned to Black Hat raising her hands.] Megan: See I read about the archaeologists who- Black Hat: I'm convinced. Gonna go to tell the internet.
[Black Hat moved closer to Megan and Cueball.] Megan: Wait, are you sure? Let me explain why I- Black Hat: Don't need it. I've heard enough.
[Zoom-in on Black Hat's head.] Black Hat: I've been looking for a weird hill to die on, and all the real ones are too far from my house. Black Hat: So this is mine. I'm now a pyramid honey truther.
[Zoom back out. Black Hat starts walking left, pointing a finger up. Cueball and Megan turn to look after him.] Black Hat: Time to start a Facebook group and post a bunch of all-caps comments everywhere. Cueball: This could have gone better. Megan: Oh well.


Backups

Explanation:
On his laptop, Cueball explores a cyclic path along which his files are being copied from storage to storage. His laptop (presumably the one he is on) is sending its files to a server, which sends its files to another server, which in turn syncs back a certain selection of files to his laptop. Cueball determines that this setup leads to an exponential growth, implying that each node in the cycle simply copies files over to the next without any effort to avoid duplicates. Indeed, each time a set of files completes a full cycle, duplicates of the same files are propagated.
Moore's Law is an observation in computer engineering (made by engineer Gordon Moore in 1965) that states that the number of transistors we can fit in a chip will double approximately every two years. Cueball, who was rather alarmed, calms down when he realizes that the exponential growth of his backup is slower than that of Moore's Law. He reasons that as long as he keeps at the forefront of information storage, he will never run out of room. Assuming available disk capacity is proportional to number of transistors (this is roughly true for solid-state disks) or otherwise keeps pace with Moore's Law, this would imply it takes more than two years for his files to completely propagate through two servers and back to his laptop enough times to double in size (implying either an extremely slow transfer or an extremely weird backup system).
The phrase "[this is] why we can't have nice things" is often used in response to incidents where someone abuses a well-meaning feature, with the abuse ultimately wiping out any benefits the feature was supposed to bring. In the comic, the person off-screen is commenting on the fact that Cueball is not using advances in storage capacity in a responsible manner. That is, rather than using the increased capacity to store more useful information, he is simply using it as a workaround to avoid having to make his backup strategy more efficient.
This concept is further expanded upon in the title text when somebody, presumably the off-screen speaker, notes that Cueball may be better off taking fewer backups in the hopes of losing some data. Typically backups are taken in the hopes of not losing programs and data. However, if the inefficient backup solution presented is representative of the other things Cueball has created, it may be better to have it all be lost and in effect force it to be re-created in a hopefully superior way.
There are some similarities to the Cueball who owns the computer in the 1700: New Bug and maybe also to the Code Quality series: 1513: Code Quality and 1695: Code Quality 2 , where Cueball speaks with Ponytail .
Poor backup strategies are referenced in 1360: Old Files
[Cueball] is sitting in an office chair at his desk, working on his laptop.] Cueball: Wait. My laptop is backing up some folders to this server...
[Cueball scratches his chin in thought.] Cueball: ...Which is backing up its archives to that server... Cueball: ...And that server is syncing certain folders over to my laptop...
[In a frame-less panel Cueball clicks on his laptop keyboard.] Click click click
[Cueball is back to working normally on his laptop. A voice speaks to him from off-panel as indicated with a starburst at the right frame.] Cueball: ...But the exponential growth is slightly slower than Moore's law, so whatever. Off-panel voice: Oh my God. Off-panel voice: You are why we can't have nice things.


Superzoom

Explanation:
In this comic, Cueball is showing off his new superzoom camera to White Hat . These are cameras with large zoom lenses, often 25× or higher magnification. He is very excited and starts by exclaiming how they can take detailed photos of the craters on the Moon , and (on better models) relatively large photos of Jupiter even with a resolution so individual clouds can be seen. (See examples of zoom on these objects here and here without cloud resolution though, but with Jupiter's four large moons and Saturn's rings .)
He then spots a bird (which is just a speck in the sky) and uses the superzoom for birdwatching , which is a popular use for these cameras. He can see that it's a peregrine falcon and that it has been banded (ringed) and he can even read the number on the band (later it seems he has more trouble locating birds with his camera in 1826: Birdwatching ). He then spots an airplane and having taken a picture of it, he can tell that it is a 787 Dreamliner from Japan Airlines , and he can even make out the registration number. All this is possible , with a Nikon Coolpix P900 , which may not be much larger than the one Cueball stands with here, with an extremely long lens, and at the time of this comics release that type of camera could be bought at Amazon for less than $600. If that is within the limit Cueball gives of a few hundred dollars can be debated ... A SX-60, refurbished with optical zoom currently sells for $379. Its predecessor, the SX-50 sold, refurbished, for less than $200 until going out of stock.
Note that before each comment he has taken a picture, presumably zooming further in after each photo of each new object, zooming out again before beginning with the next object.
Finally, White Hat exclaims that he is sold and states that he also want a superzoom camera like Cueball's. Cueball then points the camera down the street takes a picture and tells White Hat that the shop on Union Road has these camera in stock, indicating that he can see this inside the store (or in their window). He then takes another image and is able to make out not only the worker Kevin inside, he also recognizes him and (as mentioned in the title text after taking yet a further zoomed in picture) notice a stain on Kevin's shirt. He seems to like Kevin and asks White Hat to tell Kevin about the stain when he goes there to buy a superzoom camera. (This was the first time the name Kevin was used in xkcd for a fictive person, see more in this trivia ).
Even with the ability of these cameras, it would be difficult for Cueball to be able to make out a specific worker inside the store, but if he is standing near a window it is not impossible, and if he has a stain on his shirt, it is in the same league as spotting a band on a bird in the air. Of course he has to be in a spot where he can see straight to the front of the shop.
The last panel and title text is also a remark on how such cameras can be used to spy on people for quite a far distance, which has often been (mis)used by paparazzi photographers taking pictures of famous people (often while almost naked or in a bikini or other bathing clothes). Now everyman gets this disconcerting possibility to spy on their neighbors and others for just a few hundred dollars.
There are lenses that can do what Cueball describes about Jupiter's clouds in the comic (e.g., the Canon 5200mm ), but so far not such a small consumer camera as shown in the illustration.
A couple of other factors that many people may not realize until after they've bought a consumer-level superzoom camera is that a) taking a hand-held picture at maximum zoom is typically rather blurry because the lens is magnifying all vibration and it's impossible to hold the camera steady enough (so a camera tripod would be needed), and b) that the lens' aperture at maximum zoom is typically much smaller than at normal focal lengths, with the result that the shutter time must be several times longer to get proper exposure, compounding the vibration / blurry problem. Modern superzoom cameras do have "image stabilization", which can mitigate blurriness due to vibration, but extreme telephoto photography is still more challenging than implied in the comic.
Also having zoomed so much it is very hard to actually locate a moving plane or bird in the sky while looking at the image shown on the camera. And as shown in the comic the lens is zoomed very much in. Of course this could be done by Cueball after having found the flying object with much less zoom. But still if he loses sight of the bird while fully zoomed in it will be almost impossible to find it again without zooming back out.
White Hat and Cueball have discussed photography before in 1314: Photos .
[White Hat and Cueball are walking right. Cueball is looking down at a camera with a long lens he is holding in both hands.] Cueball: I love these superzoom cameras. For a few hundred dollars you can take pictures of Moon craters and Jupiter's clouds.
[They stop, White Hat looks up in the air while Cueball does the same but through the camera he is holding up to his eye while taking pictures. The camera lens is further zoomed out and is clicking.] Cueball: And birds! See that speck up there? *Click* Cueball: Peregrine falcon! *Click* Cueball: It's banded, too. Want the number?
[White Hat looks even further up as Cueball turns left and point the even further zoomed camera almost straight up while taking photos.] Cueball: And see that plane? *Click* Cueball: 787 Dreamliner *Click* Cueball: Japan Airlines. *Click* Cueball: Registration is—
[White Hat looks back down on Cueball who has turned to the right holding the fully out-zoomed camera level to the right along the ground.] White Hat: OK, I'm sold—I want one. *Click* Cueball: They're in stock at the place on Union Road. *Click* Cueball: Hey, Kevin's working today! He's great.


Horses

Explanation:
The programming of self-driving cars has been in the news lately, as engineers and philosophers debate what rules the cars should follow in dangerous situations (for instance, what to do when forced to choose between hitting a pedestrian or swerving into oncoming traffic). Ponytail suggests one approach for solving this problem: to think of the car as behaving like a horse, using its own intelligence and ignoring dangerous commands in the interests of self-preservation.
The comic begins with Ponytail claiming that in the old days, riding a horse or driving a horse drawn vehicle while drunk was less dangerous than drunk driving today. Given the higher speed and the denser traffic today this might seem plausible. On the other hand, modern cars have seat belts, airbags, and other features designed to save lives when crashes do occur; horses and horse-drawn vehicles lacked these safety features. However, if you do fall asleep on a horse, it will not suddenly walk into a tree or other obstacle, and it may actually just stop walking while you sleep.
Ponytail expands the argument by stating the horse itself will be acting in the interest of its own self-preservation. She finally states that in a comparison of the ability of self-driving cars, we should forget humans, and instead it should be the ability of horses that should be the benchmark that the self-driving cars should be judged against.
This segues into a scene in the near future where White Hat is bragging to Cueball and Megan about the features of a car (in order to sell the car to them) by comparing the features to those of horses. Car engines are traditionally measured in horsepower , which (roughly) compares the power output of the engine to that of a horse. White Hat goes a step further, claiming that the car (which is presumably self-driving) has an onboard computer with driving abilities equivalent to 3.5 horses, comparing the car's ability to mitigate for a drunk driver and/or avoid obstacles to that of a horse. White Hat has been depicted as a salesman before in 1350: Lorenz and similarly earlier in 260: The Glass Necklace .
The title text features more comparisons of the car to horses. In the text, Randall states that the car has 240% of a horse's decision-making ability and produces only 30% as much poop as a horse. This statement is absurd because it claims that the self-driving car will be producing poop. It also suggests that even with 3.5 times as much horse-intelligence as a horse, the car may only have 2.4 times the decision-making ability, although the car in the title text could also just be a different car from the one in the comic.
Note that riding a horse while drunk is in fact still dangerous and illegal in many places (for example, the UK and Ireland ). A badly-driven horse can throw off its owner, trample passersby, fall on bad surfaces, and destroy any wagon or carriage it's pulling. A self-driving car should be able to understand road rules, which a horse will not - which is presumably why the cars in the comic and the title text are both specified as being more intelligent than a horse.
In 887: Future Timeline dogs driving cars are mentioned. Self-driving cars is a recurring topic on xkcd. In 1461: Payloads spacecraft mass is measured in horses.
[Ponytail walks right with Cueball.] Ponytail: Drunk driving was less of a problem before cars. If you got on your horse drunk and fell asleep, it could just walk home.
[Zoom in on Ponytail's torso; she holds up a palm to proffer an idea.] Ponytail: And if you tried to ride into a tree, the horse could be like "No." Ponytail: Forget human drivers – that's the benchmark we should be judging self-driving cars against.
[The front end of a car, with the bottom of the windshield and the right side mirror just inside the panel is parked before White Hat. He is holding his hand, palm up, out to the left towards the car as he brags about it to Megan and Cueball standing in front of him admiring the car. At the top left of the panel a small frame with a caption is placed over the panels frame:] Soon: White Hat: This baby has 200 horses under the hood and 3.5 in the computer. Megan and Cueball: Ooooh!


Business Idea

Explanation:
In this comic, Cueball announces he has "an exciting business opportunity to share". After hearing discouragement from his off-panel audience, he promises that "this time it's a good one", and goes on to explain his plan.
Cueball's plan involves the premise that a small amount of premium gas is left in a fuel pump hose after a car driver fills their car up with premium gas. He states that even if the next customer only pays for regular gas , that they are still getting a small amount of the expensive premium gas. Though he doesn't get a chance to finish the outline for his plan, one can assume he planned to get premium fuel at regular prices, so he could then sell it for profit. After hearing the first part of his plan, two people from the off-panel audience announce they are leaving, clearly and correctly thinking that Cueball's idea is stupid and impractical.
In reality, this would be an impossible business venture to execute. While in the United States often the same hose is used for the various octane fuels, the amount of fuel contained in the hose is relatively small (about a third of a gallon , or half a liter ) compared to the amount that is generally purchased, though for motorcycles the ratio is more significant . It is also illegal to resell fuel without the correct licenses, and it would be difficult, bordering on impossible, to have the fuel pump run to just the premium fuel out, and driving to each gas station would use more money to buy more fuel than any money that could be made back. This is not to mention trying to keep track of when someone purchased premium so as to be the next person to use that pump to extract those precious drops.
1499: Arbitrage implies a similar plan to extract wealth out of a small market inefficiency that, in reality, would be far too onerous to exploit, in this case reselling the free chips offered at some restaurants. The same idea was also used in 1110: Click and Drag where a person takes free drinks to resell . See also the what if? Cost of Pennies regarding why it would not be worth trying these kind of ventures out.
The title text is another one of Cueball's fuel-based business ventures, as he says he plans to dig up fuel stations underground fuel storage tanks, to then sell the contents of. Again, illegal/theft, impractical, don't try it (though it would be much more profitable than his previous plan). The punchline is that a gas station's underground tank is "inaccessible" from the outside, just as there are some oil deposits that are inaccessible to traditional oil production techniques because no sufficient natural flow towards a well can be obtained. In the case of oil deposits, high-pressure fluids are pumped into the rock to break it up (" Hydraulic fracturing " also known as "fracking") and allow the oil to reach the well. Oil tanks, on the other hand, can be made accessible by puncturing them using (presumably) hydraulically powered tools (electrical power is inadvisable in the presence of high-vapor-pressure hydrocarbons due to the significant risk of fire and explosion caused by electrical sparking).
The title text of 1662: Jack and Jill also refers to fracking.
This comic originally shared name with 827: Business Idea , which was then renamed. There were no other relations between the ideas for the two comics, see Trivia .
[Cueball is standing next to a rolled down projector screen holding a hand up towards his off-panel audience, one from the audience speaks. It's is impossible to say if there are more than two persons off-panel, but it's also impossible to say if a person who speaks in one panel also speaks in one of the next, hence the numbering.] Cueball: Thank you all for coming. Cueball: I have an exciting business opportunity to share. Off-panel voice #1: Oh no.
[Zoom in on Cueball's head. An off-panel person speaks twice.] Cueball: Now hear me out- Off-panel voice #2: Your ideas are always the worst. Cueball: No, no, this time it's a good one! I promise. Off-panel voice #2: Uh huh...
[Front view of the screen with an image of a black gas pump, with the white hose snaking it's way up to the black handle. And arrow points to the middle of the hose where it is at it's highest point before the turn that goes to the handle. Cueball is pointing at the hose with a stick. Two different off-panel persons speaks to him.] Cueball: When someone fills their car with premium gas, some of it is left in the hose, and is dispensed to the next customer even if they've only paid for regular.  If we create a network of- Off-panel voice #3: I'm leaving. Off-panel voice #4: Me too.


Debugging

Explanation:
Cueball is telling White Hat about his attempt at debugging , i.e. the process of finding out what is causing a given (computer) problem, which can become increasingly difficult and convoluted. In this case, Cueball had a problem with his browser . His attempts to solve this problem led him to a problem with the device driver for his keyboard . Chasing that issue, he found an unclear error message from a system utility , and so on.
Cueball decides to "make a long story short" by skipping several steps he believes are boring, and he unexpectedly reveals this process has led him to find the “ Sword of Martin the Warrior ”, a legendary relic from the children's fantasy novel series Redwall . This refers to the fact that a complicated riddled path was devised in the series that would lead to the sword, which is similar to the process of debugging, as it involves following clues to achieve an answer. But apart from that, they are entirely different. [ citation needed ] This is pointed out by White Hat who states that at some point in the process he switched from the puzzle of debugging to the Redwall puzzle of finding Martin's sword. Redwall has been referenced before, most prominently in 370: Redwall ; where Martin and the sword can be seen; but also in 1286: Encryptic and more recently in 1688: Map Age Guide .
Googling an error message is a common method used during debugging, often leading to useful information. However, when there are no search results for a given message, it may mean the problem is so obscure that almost nobody had experienced it before. (See also 979: Wisdom of the Ancients about getting only one result.) Or, as the title text hints, it might mean it was a hidden clue to the location of Martin’s sword.
[Cueball and White Hat are walking, while Cueball holds a hand out while talking.] Cueball: I was trying to figure out why my browser was acting weird.
[In a frame-less panel they keep in walking, Cueball holds both hands up in front of him.] Cueball: Turns out it wasn't the browser-the issue was with my keyboard driver.
[Zoom in on Cueball's upper torso as he is holding a finger up.] Cueball: Debugging that led me to a mysterious error message from a system utility...
[Zoom out as Cueball holds up a miniature sword by the blade in one hand. White Hat turns his head around and looks at it while they keep walking.] Cueball: Anyway, long story short, I found the sword of Martin the Warrior. White Hat: I think at some point there you switched puzzles.


Meteorite Identification

Explanation:
Meteorites form when a meteoroid survives entrance through the Earth's atmosphere as a meteor . Thus, they are very rare rocks that come from space, and can stem from broken asteroids , the Moon , and sometimes (very rarely) even from Mars .
The flowchart , though facetious, would actually work the vast majority of the time a person picks up a rock and believes it to be a meteorite, since any single rock one finds on the surface of the earth is almost definitely not a meteorite.
Flowcharts are often used ( in xkcd ) to give the inexperienced a step-by-step process to follow (see a guide to flowcharts here: 518: Flow Charts ). Meteorite identification, however, is very difficult, so the brevity of this flowchart in a way pokes fun at the need for a flowchart to identify meteorites, since laypeople are not experienced enough to confirm that a rock is indeed a meteorite. A similar short flowchart as this has been used recently in 1691: Optimization , and another only two box chart was used in 1195: Flowchart .
In the title text Randall mentions that the comic image is a link to the more detailed  (now defunct, mirror here ) Meteorite or meteorwrong? Self-Test Check list flowchart at the Department of Earth and Planetary Sciences at Washington University in St. Louis .
The authors of those resources notes that they have received many rock samples and photos (or even personal visits) from people claiming to have discovered meteorites and thus they would likely benefit from just providing people the shortcut flowchart from Randall, as a way of saying, "leave meteorite identification to the professionals."
Randall also mentions in the title text that his favorite part of this real flowchart, which is the part where if anyone saw the "meteor" fall then it is 'NOT A METEORITE.' What he most likes about it is that this is not a mistake.
First of all the chance of actually being near a falling meteorite is exceedingly small. From the flowchart was a link to a 64 point long checklist, which basically all ends in "..., then it's not a meteorite." In point 3 is noted the following:
Since 1900, the numbers of recognized meteorite "falls" is about 690 for the whole Earth. That's 6.3 per year. Only 98 of those occurred in the US. That's less than 1 per year. Even when a meteorite is observed to fall, experienced meteorite hunters may find only a few stones when hunting dawn to dusk for a week.
Second, meteors that can be seen falling almost definitely cannot be found on the ground immediately after.  Any meteor big enough to glow and be visible while falling all the way to the ground will leave a large impact crater, rather than simply sit on the ground as a rock.  Smaller meteors do not fall fast enough to glow all the way to the ground. Either they will burn up completely (not leaving any meteorite) or they will be slowed down before they burn all the way up (but typically end up much smaller than the original meteoroid). After that they will stop glowing and will brake even further until they reach a terminal velocity due to air resistance. Their small size, and lack of glow, make them practically impossible to follow with the naked eye even in daylight. If a person stands close by the impact location of a meteor it may be possible to hear a swish and a thunk, from when it passes by and then hit the ground. It will then be possible to locate the meteorite, but such a falling stone could also have been dropped from an airplane or by a storm. But in some few cases people have actually heard a real meteor falling and found it afterwards. This is what happened with the 690 events mentioned above. All this is described on How to Identify a Meteorite from The Meteorite Market which is linked in point 48 in the table from Washington University. But they did not see it fall!
What Randall finds so funny about this part of the flowchart is that there are three arrows leading to the question "Did someone see it fall?", but from there only a "Yes" option is possible, and then this gives the result "Not a meteorite." This indicates that if you have found a rock that has no dark crust or regmaglypts (the options that by saying no takes the user to the question about seeing it fall), then it is not a meteorite, and then the only reason people might still believe it to be a meteorite must be because someone saw it fall and assumed it came from space (rather than more likely scenarios, such as a stone coming loose from a cliff or building, or being dropped by a bird or aircraft).
If the rock actually has those thumbprint like impressions on the surface (that scientists call regmaglypts ) then the creator of the flowchart actually asks to see the rock (photo or sample). The other features that are interesting is if it has a dark thin crust (from the melting during entry), but only if it also has either regmaglypts or if it has a lighter color inside than the outer crust.
See also 1405: Meteor about how people mistake the words meteorite with meteor. The many misspellings of meteorite is mentioned in point 63 in the table.
[A caption is above a flowchart with only two boxes. The first box is a diamond shaped box with an arrow down to the next rectangular box below. Each box has a text.] How to identify a possible meteorite: Start No, it's not a meteorite.


Proofs

Explanation:
Miss Lenhart is teaching a math class. She begins a proof when one of her students ( Cueball ) interrupts her asking if this is one of those dark-magic (unclear, incomprehensible) proofs. She claims no, but in a matter of seconds Cueball is calling out that he was right.
The proof she starts setting up resembles a proof by contradiction . However, after Cueball's interruption Miss Lenhart's proof takes a turn for the absurd: rather than assuming there will be a point in the function that correlates to co-ordinates (x, y), Miss Lenhart assumes that the act of writing numbers on the board will correlate to co-ordinates (x, y).
A normal proof by contradiction begins by assuming that a particular condition is true; by demonstrating the implications of this assumption, a logical contradiction is reached, thus disproving the initial assumption. One example of a proof by contradiction is the proof that √2 is an irrational number:
Q.E.D.
Alternatively, instead of a proof by contradiction the setup could be for a one way function. For example, it is relatively easy to test that a solution to a differential equation is valid but choosing the correct solution to test can seem like black magic to students.
The way that Ms Lenhart's proof refers to the act of doing math itself, is characteristic of metamathematical proofs, for example Gödel's incompleteness theorems , which, at first sight, may indeed look like black magic, even if in the end they must be a "perfectly sensible chain of reasoning" like the rest of good mathematics. While typical mathematical theorems and their proofs deal with such mathematical objects as numbers, functions, points or lines, the metamathematical theorems treat other theorems as objects of interest. In this way you can propose and prove theorems about possibility of proving other theorems. For example, in 1931 Kurt Gödel was able to prove that any mathematical system based on arithmetics (that is using numbers) has statements that are true, but can be neither proved nor disproved. This kind of metamathematical reasoning is especially useful in set theory , where many statements become impossible to prove or disprove if the axiom of choice is not taken as a part of the axiomatic system.
Using a position on the blackboard as a part of the proof is a joke, but it bears a resemblance to Cantor's diagonal argument where a position in a sequence of digits of a real number was a tool in a proof that not all infinite sets have the same cardinality (rough equivalent of the number of elements). This "diagonal method" is also often used in metamathematical proofs.
The axiom of choice itself states that for every collection of nonempty sets, you can have a function that draws one element from each set of the collection. This axiom, once considered controversial, was added relatively late to the axiomatic set theory, and even contemporary mathematicians still study which theorems really require its inclusion. In the title text the decision of whether to take the axiom of choice is made by a deterministic process, that is a process which future states can be developed with no randomness involved. Determinacy of infinite games is used as a tool in the set theory, however the deterministic process is rather a term of the stochastic processes theory , and the dynamical systems theory , branches of mathematics far from the abstract set theory, which makes the proof even more exotic. The axiom of choice was mentioned earlier in 804: Pumpkin Carving and later in 982: Set Theory , another comic about a math class with a similar theme on how teachers teach their student mathematical proofs.
Although Miss Lenhart did retire a year ago after 1519: Venus , she seems to have returned here for a math course at university level, but continues the trend she finished with in her prior class. A very similar Miss Lenhart comic was later released with 2028: Complex Numbers .
[Miss Lenhart is standing facing left in front of a whiteboard writing on it. Eleven left aligned lines of writing is shown as unreadable scribbles. A voice interrupts her from off-panel right.] Miss Lenhart: ... Let's assume there exists some function F ( a,b,c ...) which produces the correct answer- Cueball (off-panel): Hang on.
[In a frame-less panel Cueball is sitting on a chair at a desk with a pen in his hand taking notes.] Cueball: This is going to be one of those weird, dark magic proofs, isn't it? I can tell.
[Miss Lenhart has turned right towards Cueball, who is again speaking off-panel. The white board is also off-panel.] Miss Lenhart: What? No, no, it's a perfectly sensible chain of reasoning. Cueball (off-panel): All right...
[Miss Lenhart is facing the whiteboard again writing more scribbles behind some of the lines from before (the first line has disappeared). The lines that have more text added are now number three and five (four and six before). Cueball again speaks off-panel.] Miss Lenhart: Now, let's assume that the correct answer will eventually be written on the board at the coordinates ( x, y ). If we— Cueball (off-panel): I knew it!


Linear Regression

Explanation:
Linear regression is a method for modeling the relationship between multiple variables. In the simplest case, it can be used for two variables wherein the model determines a " best-fit " line through a scatter plot of the datasets, together with a coefficient of determination , usually denoted r 2 or R 2 . When only two variables are included in the regression, R 2 is merely the square of the correlation between the two variables. R 2 is a number between 0 and 1 that indicates how well one variable can be used to predict the value of another. A value of 1 means perfect correlation, while a value close to 0 indicates a weak relationship between the variables.
A constellation is the region of sky containing an asterism ; an asterism is a pattern created by linking the apparent positions of stars as seen in the sky from Earth. Strictly speaking, Randall's "Rexthor" is an asterism, although "constellation" is used informally in place of "asterism" by even seasoned astronomers. Different civilizations have recognized different constellations (the modern IAU, for example, lists 88 "official" constellations), and one could create their own constellations by connecting assorted points.
In this comic, a set of data has had linear regression and some form of statistical analysis applied to it, indicating that there is low correlation between the two. The data points are so widely scattered that (as noted in the comic) it is easier to connect the data points in a constellation-like pattern than it is to determine whether the correlation is negative or positive (without looking at the trendline, of course). Because of this, Randall suggests we should be suspicious of any conclusions drawn from this data.
The comic is somewhat misleading, since the data in the graph actually has an R 2 of 0.02, only a third of what Randall claims.  An example of published research with an R 2 of 0.06 where the association in the graph is noticeable (if not strong) can be found here (figure 2 has r = 0.25 which corresponds to R 2 = 0.06). In addition, it is hard to see the association in the comic's graph because relatively few points are plotted. In a data set with 1000 observations and R 2 = 0.06, any association between the two variables would be quite clear.
The lines connecting the stars in this "constellation" create a crude illustration of a person with an outstretched arm holding up a dog, which could be a reference to the film Life is Beautiful where a waiter carries a dog on his tray without realizing. The name "Rexthor the Dog Bearer" could be a spoof on Thor , a Norse god who wields a hammer. By replacing his hammer with a dog and adding "Rex" (an archetypal dog name, but also meaning king as in king of the dinosaurs T-rex), Randall may have created a comical, dog-bearing version of Thor.
The 95% confidence interval in statistics is such a range of an estimate, that it is expected to contain the real value (the estimated population parameter) 95% of the time. The confidence interval is a standard method to provide evaluation of the estimation error in statistics. On the right panel the resulting estimate seems to be a drawing, so the 95% confidence interval would be a set of drawings, expected to contain the correct drawing in 95% of samples where it is calculated. According to the title text, the interval in this particular sample also includes a cat and a teapot, so we can only make extremely vague statements in order to maintain 95% confidence.
The teapot may be a reference to Russell's teapot , or possibly to the "teapot" asterism in the constellation Sagittarius. Alternatively it is just because the "dog" actually looks more like a teapot than a dog, and Randall noticed this and added it in the title text. In the latter case, the two first suggestions are just another example on how humans see patterns also where there are none to find, like those of pareidolia mentioned in 1551: Pluto .
[Two square panels show identical sets of scattered black dots, with only the red additions being different.]
[The left panel shows a slightly rising red line drawn through the middle of the panel, passing near a few dots but not obviously related to most of them. A red text is below the dots:] R 2 =0.06
[The right panel shows many of the dots connected by red lines to form a stick figure of a man resembling the constellation Orion, with the hand on the reader's right raised and holding an object. A red text is below the dots:] Rexthor, the Dog-Bearer
[A caption is below and spanning both panels:] I don't trust linear regressions when it's harder to guess the direction of the correlation from the scatter plot than to find new constellations on it.


Unicode

Explanation:
Cueball is a highway engineer that has been placing two traffic signs in a river trying in vain to guide the water flow and thus he ends up talking to the water trying to make it take a detour instead of going under the bridge. On the distant bank two other engineers are arguing, with gestures, in presumably a heated manner (probably about where to place a third sign, lying next to them at the the water, to make it behave a certain way)
As rivers flow according to the landscape, this plan will not work and the river will continue on its course. Cueball is very frustrated by this and is still trying to make the river obey the traffic laws. The caption lays out the punchline: The comic compares the useless approach of Cueball attempting to divert a flowing, moving river with fixed signs that do nothing, with the Unicode Consortium 's attempt to define the diverse and ever-changing human language with strict technical standards.
Unicode is a largely successful attempt to have a standard for representing all possible letters, numerals, digits and symbols that make up human writing in all languages.  This includes the roman letters used in this article, characters with modifiers like ê (both with the common characters as well as the modifiers selectable separately), logographic characters like in Chinese, syllabic writing system like Japanese, right-to-left and/or top-to-bottom writing systems, mathematical symbols and many other writing systems.
Emoji , one of the trendier and newer Unicode blocks, are also referenced in the title text (see below). The symbols on the signs in the river are real road signs, but interestingly enough they also both exist in Unicode, with the warning sign triangle with an exclamation mark ⚠ having code (U+26A0) and the black, rightwards arrow ➡ having code (U+271A) .  As can be imagined, coping with the wide variety of character sizes, orientations, ways they can be modified, capitalization rules, etc. can get to be very challenging as the Unicode Consortium tries to write rules that accommodate how printed language is actually used. Emoji have become a recurrent theme on xkcd.
The title text refers to a proposal to add three dinosaur heads to the official list of emoji.
This is likely to stir a glorious internet argument between a half-dozen opposing (and pedantic ) camps that may now be brought together, such as the following:
See also this discussion about this comic on the Unicode mailinglist ...
Highway engineers were also the subject of 253: Highway Engineer Pranks and 781: Ahead Stop .
[Cueball is standing in a river close to it's right bank, the water reaching up to his thighs. He is holding on to a traffic sign standing towards right. It has a label and an arrow below this pointing to the right bank. With his other arm he is pointing to the left at the advancing water masses. Further up the river is another street sign this sign has an exclamation mark inside a triangle. The water flow is indicated with several lines on the river surface, mainly moving along the river, but around Cueball and the signs there are circular lines. In the distance on the left bank of the river two people are standing and making gestures with raised arms. The left has white hair (could be either sex) and the other is a Cueball-like guy. A third sign is lying on the ground to the left of them face down. Behind them is a slope up to a road with a parked car. The road continues out over a a bridge that crosses the river. The river which passes under it both left and right of a central pillar. At that distance the right bank of the river (and thus the right end of the bridge) is not visible, being outside the panel. On each river bank grass can be seen and on the right bank also a small stone.] Cueball: No, go this way, not- Cueball: Are you even listening!? Cueball: ... Hey! That's not what that area is for! Sign with arrow: Detour Sign with triangle: !
[Caption below the panel:] Watching the Unicode people try to govern the infinite chaos of human language with consistent technical standards is like watching highway engineers try to steer a river using traffic signs.


Number of Computers

Explanation:
This comic shows a semi-log plot with two red lines. The first line shows the increasing rate that computers have been created since the first came around in the 1940s. The graph shows this to occur around 1946. ( The precise date can be discussed but it was around that time that the concept began to be applied to real working machines.) After the first computer, the number of computers created is shown to increase in a roughly straight line, indicating exponential growth . At the time of this comic's release in 2016, the curve has passed 10 billion computers, and its projection into the 2020s predicts that the number of computers will keep rising exponentially for at least 10 years to come.
The other plot on this graph represents all the computers destroyed by throwing them into Jupiter . So far this is only true for the computers on two space probes : those on the Galileo orbiter and its probe . The latter's mission was to fly into Jupiter so it went first in 1995; the orbiter went only after it had completed its mission in 2003. That constitutes the first two steps on the graph.
Recently the Juno space probe entered into orbit (as only the second after Galileo), and that was celebrated with 1703: Juno on xkcd. Juno's main mission has hardly begun yet; as at the time of this comic's release, it is not even in its final orbit. But once its mission is completed, it will also crash into Jupiter thus destroying a third computer. This is shown as the third step, but this section is shown with a dotted line, as the destruction may still fail if NASA loses contact with the probe before giving it the order to deorbit into Jupiter. This is scheduled to occur in 2018. All three steps on the graph fits with these years. (Note the number of computers created is not drawn with a dotted line into the future, probably because Randall believes this continued increase in numbers of computers to be quite certain over the next 10-20 years, whereas the outcome of a space probe mission is never certain, even when the probe is already in orbit and only 1½ years before scheduled deorbit!)
Space probes sent to Jupiter are typically scheduled to deorbit and fall into Jupiter's atmosphere. There can be several reasons for this, but one very important reason is to avoid contaminating Jupiter's moons with Earth pathogens , especially the four Galilean moons including Europa which may harbor life . Also the huge gravity well of Jupiter that would have to be overcome for such a probe to leave the planet again makes it impossible to have an orbiting probe return to Earth with samples.
The caption below the comic humorously implies that NASA's reasons for causing the probes to deorbit into Jupiter is merely an attempt to destroy all the computers of the world. The caption notes that they are failing horribly, given that they have destroyed only three computers out of more than 10 billion. However, due to the semi-log scale, those three computers appear to have more significance than they actually have. The caption states that NASA really needs to pick up the pace (having only destroyed two since the 1940s, when computers were created), if they wish to actually finish the job of destroying all computers by hurling them into Jupiter. In addition, seeing as there have been many computers destroyed by other means, NASA will never actually catch up, no matter how hard they try, making this statistic even more irrelevant.
Destroying unwanted objects by hurling them into Jupiter pokes fun at the common science fiction trope of destroying objects by hurling them into the Sun [1] .  Hurling objects into the Sun is in fact extremely difficult because of the need to cancel out the orbital velocity of the earth.  Randall may be referencing calculations ( [2] , see item 11) that show that hurling items into Jupiter requires 38% less energy than hurling them into the Sun.
The title text continues the caption by mentioning that in NASA's annual reports they try to make their numbers look better by counting the redundant computer systems on Galileo and its probe, thus doubling the numbers of destroyed computers to four. This of course makes no big difference given the exponential growth of computer production, which is also noted. This indicates that this is a top priority for NASA. That NASA might try to make themselves look better in a report by doubling a number could be realistic, presumably for political reasons or to get better funding.
[A graph with two red lines. The X-axis is a time-line with eight ticks with every second tick labeled below the axis, ranging from around 1940 to 2030. The Y-axis is a logarithmic count ranging from 1 to 1 billion. There are 12 ticks with the first and then every third tick after that larger than the two ticks in between. All the large ticks are labeled, but only the first two of the small ticks are similarly labeled. Labels are written to the left of the axis. All labels on both axes are written in gray. The first red line is a straight line (thus exponentially growing), starting close to the bottom left corner eventually reaching the upper right edge of the graph. The other red line begins around 1990 and has three straight steps. Each step is labeled with gray text, the last part of the line (after the present 2016), is dotted. Both of the red lines have an arrow pointing to them with a label above the arrow.] Left red line: Number of computers created Right red line: Number of computers destroyed by hurling them into Jupiter Labels on right red line: Galileo probe Galileo orbiter Juno (scheduled) Y-axis: 1 billion 1 million 1,000 100 10 1 X-axis: 1960 1980 2000 2020
[Caption below the panel:] NASA needs to pick up the pace if they ever want to finish the job.


Cron Mail

Explanation:
On Unix -like systems, cron is a system utility that runs tasks on a schedule.  This program has been around since the early days of Unix and has not changed much - it is still one of the most widely used functions in modern operating systems.  Many administrative tasks on servers are automated using cron, including monitoring and updates.
When a cron job produces output, cron's default behavior is to send an email to the user account under which the job ran.  However, in most situations, an email address has not been set up for that user, so the email is instead written to a mailbox file.  Most Unix shells will notify the user with a message like "You have new mail" when this mailbox file is updated, but if the user doesn't know how to check this mail file, they will likely just ignore the message.
In this case, Cueball has been ignoring his mailbox for fifteen years.  When he finally learns where to look, he discovers more than a gigabyte worth of messages from the cron program, the vast majority of which are likely meaningless.  Ponytail says to Cueball "fix your cron" (likely meaning he should fix the task that's generating the output so that it doesn't do so), then set a parameter that tells cron to send email to an address he actually checks.  (He could also opt to direct the mails to /dev/null , which would discard them, or simply disable the mail in the crontab.)  Cueball, however, interprets the tremendous amount of email as spam and decides to redirect the emails to /etc/crontab , the main configuration file that contains all of cron's scheduling information.  He apparently believes that this will either stop the emails or cause cron to spam itself instead.
In reality, this will not cause significant problems as the MAILTO environmental variable in cron takes an email address or usernames on the local system and attempts to send emails to them.  It will not write or append output to a local file like /etc/crontab .  Thus when cron attempts to email /etc/crontab the mail program cron uses will generate an error saying it can't find the user /etc/crontab .
For example, if you create the following crontab:
installed on a user named me on a system called mycomputer then you will see a new error messages email to you (located in /var/mail/me ) stating it can't send email to a user named /etc/crontab and the undelivered email is being returned to the sender.  The error email will look like the following:
The title text shows that Cueball is somewhat aware of what cron does, including the fact that it's existed pretty much unchanged for several decades, but he hasn't bothered to really get into understanding it, treating it more as a foe to vanquish rather than as a tool to understand and use.
[Cueball is sitting at a table in an office chair working on his laptop. Ponytail walks up to him.] Cueball: I've been getting these "You have new mail" UNIX notifications for like 15 years, but I've never bothered to figure out what it's talking about.
[Ponytail has stopped behind Cueball who is typing on his laptop. When Ponytail (and later Cueball) mentions code, the text uses both small and capital letters (as opposed to only capital letters in all other text).] Ponytail: Look in /var/mail? Cueball: OK... Cueball: Oh, wow, there's like a gigabyte of stuff from Cron in here.
[In a frame-less panel Ponytail is facepalming. Cueball is replying from off-panel with a starburst indicating his position.] Ponytail: *Sigh* Ponytail: You should fix your Cron, then point "MAILTO=" somewhere you actually see- Cueball (off-panel): Better idea:
[Same setting as panel 2 but Cueball is visibly typing on the laptop as shown with three small curved lines over his hands on the keyboard.] Cueball: export MAILTO=/etc/crontab Cueball: There. Your move, Cron. Ponytail: Wow. Hardball. Cueball: Let's see how important it thinks that mail really is.


Migrating Geese

Explanation:
Migrating refers to the changing of a habitat, which happens every year with birds like geese that travel long distances to avoid cold seasons and get back to the food in the summer time. When geese fly to their new habitat, they tend to fly in a very clear V formation . The V formation improves the efficiency of flying birds, particularly over long migratory routes. All the birds except the first fly in the upwash from one of the wingtip vortices of the bird ahead. The upwash assists each bird except for the "leading" one in supporting its own weight in flight, saving them up to 20% of the energy needed.
It should be noted that geese do have family structures with adult geese in "alpha" positions, but not a strict ranking order. An individual's position in formation flights is coincidental and constantly changing, so that the goose at the point of the formation can pull back and rest in the V wings while others "lead" the swarm. Popular earlier beliefs about an "alpha goose" heading a formation for the entire flight is a myth, easily disproved by watching geese formations in flight.
This comic shows such a formation with 20 geese, with several geese and areas in the V formation labeled, giving different roles to the geese and assigning these areas a new meaning. See the table below .
Apart from a "twin engine" goose in the bottom right arm of the V the only part of the formation that would not normally be seen is Kevin, who flies off at a 45-degree angle. In that direction there is no aerodynamic help from the other birds, and in the title text the rest of the geese also exclaim, "Dammit, Kevin" when he (again?) tells them that he has a great new idea for a migration (maybe referring to the new direction). This is either a reference to the fact that migrating birds manage to consistently arrive in the same general area every year, or to the way that vacations are sometimes suggested (by humans): "I thought of an idea for a vacation..." This was only the second time the name Kevin was used in xkcd for a fictive person, see more in this trivia .
[Caption above the panel:] Understanding Migration of Geese
[20 geese are shown flying in a typical migratory V-formation. As they are shown in silhouette it is not possible to determine if they are seen from above or from below.  They are flying toward the top of the image with the first goose close to the top in the middle of the image.  There is one head goose, and then there are 7 geese in the left arms and 9 geese in the right arm. Behind the left arm there are two stragglers that are not in line with the others, but closer to the middle than those above and not as close to each other as the rest but still flying in the same direction. Finally there is one goose at the bottom right corner flying at a 45 degree angle away from the other to the right. The first goose is flapping its wing, which is also the case with six other geese, no. 4 and 6 in the left and 3, 5 and 6 in the right arm as well as the middle of the two in the rear towards the middle. The rest are soaring with straight wings and all of these look the same except no.  7 in the right arm which has two tails, which both goes ahead of the wings, making it look like a plane with two engines. The head goose and 5 of the 9 geese in the right arm as well as the one bottom right are labelled with and arrow pointing to them from the label. The front goose has the label in front to the left, the other have it in front to the right, except the second last in the arm which has the label inside the V and one flying away which has the label right above it. The two behind and right of the left arm have one label behind them with two arrows from the label pointing at both geese. There is a thick curvy line in front of geese no. 3 to 5 in the left arm. In front of that line is a thinner broken line. In front of this is a label written with the same curvature. There are two areas surrounded by dotted lines. The first one is behind the last of the left arms geese, extending in the same direction for a distance of about two geese. It has a label above and left with and arrow pointing to it. The other area is in the middle of the V forming a loose triangular structure with a label inside.] Head goose:  Head goose (4 th in line to the British throne) Right no. 1: Quarterback Right no. 3: Comptroller Right no. 5: Migration abort goose Right no. 7: Twin-engine model Right no. 8: CIA informant Bottom right corner: Kevin Behind center: Backups In front of left no. 3-5: Shock front Empty area behind left arm: Missing valence geese Empty area in center: Stealth cargo being escorted


Starshade

Explanation:
Megan and Ponytail are talking about space telescopes in general. Megan says that these telescopes could see exoplanets better by using occulting disks , in the form of free floating opaque discs, that could block out light from the exoplanets' stars, thus enabling the telescopes to see the weak light from the planets when the glare of the stars has been diminished.
She continues by explaining that the scientists behind the new James Webb Space Telescope , at the time of the comic scheduled to launch in 2018, thought about including such a disk (a starshade ), but that it was cut for budget reasons . Ponytail asks if it has to be their own disk, and then decides to kickstart a fundraiser to build a starshade. Ponytail is referring to the crowdfunding site Kickstarter , although there is no actual project for a starshade for Webb (or for the New Worlds Mission; see title text explanation) on Kickstarter. Megan asks her to at least warn the scientists if she makes the starshade, but Ponytail just replies "whatever".
The final panel shows the NASA control center in 2018 when the Webb telescope is being calibrated. It turns out that Ponytail succeeded and did indeed not warn the scientists. Cueball is surprised by the disc -- and possibly by what the disc might have printed on it, given its crowdfunded origins -- but Hairbun immediately notices exoplanets, implying that Ponytail's plan worked.
Note that the telescope has partners from 20 countries and is being operated not only by NASA but also by European Space Agency (ESA), Canadian Space Agency (CSA), and the Space Telescope Science Institute (STScI).
The best known space telescope is the Hubble Space Telescope , which was launched back in 1990. The Webb telescope is seen as a successor instrument to Hubble and, because its instruments are designed to work primarily in the infrared region of the electromagnetic spectrum, also as a successor to the Spitzer Space Telescope launched in 2003. In addition to having more sensitive sensors and being larger, Webb will also be located near the L2 Earth–Sun Lagrangian point , and thus not in orbit around Earth. This means that it can keep focusing on a specific point for longer times, while Hubble can see a given point for only about half an hour before moving behind Earth again. When operating in the infrared range as the Webb telescope does (from middle infrared to red and orange visible light), it is important to be outside the atmosphere or at least on very high mountains. Another important feature is to keep the temperature constant and very cool. Since the Webb telescope is always in the light of the sun, this is achieved using protection from a large sunshield .
The title text mentions the New Worlds Mission . This mission is to find exoplanets (hence the name New Worlds) by applying a starshade to block the light of distant stars, so that the planets around the stars are more visible. All discovered exoplanets so far have been found indirectly and not by direct visual observation. The starshade proposed by the New Worlds Mission is a spacecraft designed to work in tandem with a space telescope (not necessarily just the Webb telescope). It is a large occulter that blocks a star's light. One problem with this concept is that light coming from the target star would diffract around the disc and constructively interfere along the central axis. Thus the starlight would still be easily visible, making planet detection impossible. In order to avoid this problem, the proposed starshade is a sunflower-shaped coronagraph disc. The "petals" of the "sunflower" shape are designed to eliminate this diffraction, making exoplanet observation possible. The starshade would fly 72,000 km (45,000 mi) in front of a space telescope (between the telescope and a target star) in order to work. A video demonstrating the starshade is available on the Wikipedia page for the New Worlds Mission. The title text explains that NASA actually sponsored this mission's proposal to build a starshade for the Webb telescope, and concludes that the surprise shown in the comic is not likely to occur in real life. NASA stopped this sponsorship in 2008, and the New Worlds Mission has been looking for additional financing since 2010. Telescope people refers to the engineers and scientists who build, operate, and use space telescopes.
It seems clear that Randall would like to point attention to the New Worlds Mission, possibly hoping for increased funding for the project so a starshade could become a reality for the Webb telescope. That Randall is interested in exoplanets has been demonstrated many times in xkcd.
Note that two of the Webb telescope's instruments , the NIRCam and the MIRI, feature starlight-blocking coronagraphs for observation of faint targets such as exoplanets, so the telescope has ways to improve the visibility of these planets. However, Randall (and the New Worlds Mission) believe that a starshade would be better suited for this task.
The idea of an occulting telescope was used in 975: Occulting Telescope , where it turns out the purpose is to just block all star light, not to see exoplanets.
[Megan and Ponytail are walking.] Megan: Space telescopes could see exoplanets better if they used free-floating opaque discs to block the stars' glare.
[They stop walking in this zoom in on their heads. Ponytail has turned towards Megan.] Megan: They thought about including one with the Webb telescope, but cut it to save money. Ponytail: Well... does it have to be their disc?
[In this frame-less panel Megan is left standing as Ponytail turns and walks away.] Megan: What do you mean? Ponytail: Like, if I Kickstart a starshade for them? Megan: Um. Would you at least warn them? Ponytail: Eh. Whatever.
[Cueball and Hairbun, both wearing headsets, are sitting on one legged stools on either side of a slim desk with two computers screens on top of it. Each are looking at their own screens while typing on a keyboard in front of them. Hairbun is pointing at her screen. A small frame is overlaid on the top of the panels frame with a caption:] NASA, 2018: Cueball: Initiating Webb calibrat- Cueball: Aaaaa ! What the hell is that!? Hairbun: Hey, look, exoplanets!


Wrong

Explanation:
All matter that we encounter in everyday life is normal matter and not antimatter . Atoms, while once when they were named believed to be the smallest unit of matter, are now known to be made up of protons , neutrons and electrons . Protons and neutrons are in turn made up of quarks , which are fundamental particles (meaning not made of other particles). Quarks come in six different " flavours " (up, down, top, bottom, charm, and strange), with protons and neutrons being made of up and down quarks. Each flavour also has a corresponding antiparticle , an antiquark, which would make up antiprotons and antineutrons.
White Hat and Megan appear to be discussing the topics of antimatter and subatomic particles. White Hat makes the assertion that we (referring to people and objects) are made partially of antimatter, because, as he claims, a proton (one of the particles which make up all matter) is made of two quarks and an antiquark. In fact, protons are made up of two up quarks and a down quark, which are all not antiquarks. He is likely making the mistake of mixing up the "up" and "down" flavours of quarks (which can be seen as complementary flavours of quarks) and mistaking them to be mutual antiparticles. He continues to elaborate on his idea by mentioning neutrons, which are made of two down quarks and an up quark.
When Megan (accurately) doubts his claim, White Hat takes out his smartphone to look it up, in order to show Megan that he is correct. However, upon researching online, he realizes that he was, in fact, wrong (hence the title of the comic). Not wanting to admit being incorrect or yield his position in the discussion, he convinces himself that he wasn't actually wrong, as depicted by his mentally erasing the realization that he was wrong. Instead, he completely changes the topic to try and re-frame it so that he is not wrong. In this case, he circles back and criticizes the entire scientific concept of "particles", which can be seen as an attempt at a straw man on his part. Presumably, he will go on to explain how humans are not made of particles and quarks, but of waves.
It is rather common to be unwilling to admit fault (the whole topic of this comic) and to instead try to maintain an air of infallibility and intelligence. Some people are just too prideful to admit that they are inherently fallible. White Hat is one of those people, as depicted in several of his earlier appearances (see trivia section ). Randall uses this comic to criticize people who are unable to put aside their ego and re-assess what they know in the face of empirical data. Such thinking flies directly against scientific rigor (adding an extra layer of irony to the situation, since White Hat and Megan are discussing a scientific topic). This method had already been called wrong in 803: Airfoil .
White Hat's new topic, where he can be right, includes the quantum field theory , a very complicated field, which it is likely one Megan is not well versed in (inferred by the fact that she was not quite sure about the anti-quarks). So he may be raising the topic because he believes she will not understand it sufficiently to refute his correctness. Megan, however, recognizes exactly what he is trying to do, and can only sigh in response to his failed efforts. In the QFT, particles are often described as resonances or excited states of the underlying physical field, in the same way as photons may be thought of as excitations in the electromagnetic field; in this way White Hat appears to be dismissing his earlier errors by implying that particles are merely an effect of something more complex, of which he can demonstrate his knowledge. Furthermore, in quantum field theory quarks do not exist in the conventional sense.
In the title text, White Hat just remembers another thing he's right about. This demonstrates even more clearly that he is not interested in a discussion on the merits of a topic, but instead is seeking only recognition and validation for being right. This bears some similarity to 386: Duty Calls , in which Cueball stays up late correcting someone on the Internet, and 2051: Bad Opinions , where Cueball actively seeks out people with bad opinions for him to correct.
White Hat may have incorrectly remembered that, while the valence quarks in a proton are all matter, quantum field theory says that protons also contain an indefinite number of "virtual" anti-quarks, quarks, and gluons. See this video What are Quarks? about this. His final comment could be referring to the ontological debate over whether virtual particles are in some sense real or only an artefact of perturbation theory. Alternatively, he may have been confused by the fact that negatively charged quarks contribute negatively to baryon number. <!-- I think that that's incorrect; could you be thinking about strangeness and bottomness instead? I'm not wrong, but let's talk about something else that I'm right about instead. -->
[White Hat is walking beside Megan, index finger extended] White Hat: Really, we're all made of antimatter. A proton consists of two quarks and an antiquark. Megan: ...I don't think that's right.
[White Hat stops to take out his smartphone tapping on it. Megan stops and turns towards him.] White Hat: Sure it is. Neutrons are, too. Megan: Do you mean "up" and "down" quarks? I think antiquarks are a different thing. White Hat: No, let me show you... Tap Tap
[Zooming in on White Hat's head, while he is holding his phone up looking at it. He is thinking as shown with a bubbly thought bubble.] White Hat (thinking): I'm...wrong?
[White Hat has lowered the phone. He is still thinking the same but the text has been scribbled out.] White Hat (thinking): I'm...wrong?
[White Hat purges the thought from his mind] White Hat (thinking): ...
[Similar setting as in the first panel, but in a full row wide panel, and White Hat is still holding his smartphone] White Hat: Really, the whole idea of "particles" is inaccurate. These are abstractions arising from quantum field theory, but what most people don't realize is... Megan: *Sigh*