https://www.explainxkcd.com/wiki/api.php?action=feedcontributions&user=Captain+Video&feedformat=atomexplain xkcd - User contributions [en]2024-03-28T08:28:44ZUser contributionsMediaWiki 1.30.0https://www.explainxkcd.com/wiki/index.php?title=2883:_Astronaut_Guests&diff=3332252883: Astronaut Guests2024-01-20T03:26:53Z<p>Captain Video: /* Explanation */</p>
<hr />
<div>{{comic<br />
| number = 2883<br />
| date = January 19, 2024<br />
| title = Astronaut Guests<br />
| image = astronaut_guests.png<br />
| imagesize = 331x391px<br />
| noexpand = true<br />
| titletext = They didn't bring us a gift, but considering the kinetic energy of a bottle of wine at orbital speed, that's probably for the best.<br />
}}<br />
<br />
<br />
==Explanation==<br />
{{incomplete|Created by SIX ASTRONAUTS OVER YOUR HEAD RIGHT NOW - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
By exploiting ambiguities in the English language, it is possible to truthfully - if misleadingly - claim that you had the personnel of the International Space Station "over" when it passes above you.<br />
<br />
This comic was posted the same day as the American release of a film set on the ISS (conveniently named ''{{w|I.S.S. (film)|I.S.S.}}'').<br />
<br />
==Transcript==<br />
{{incomplete transcript}}<br />
<br />
{{comic discussion}}</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2883:_Astronaut_Guests&diff=3332242883: Astronaut Guests2024-01-20T03:24:10Z<p>Captain Video: </p>
<hr />
<div>{{comic<br />
| number = 2883<br />
| date = January 19, 2024<br />
| title = Astronaut Guests<br />
| image = astronaut_guests.png<br />
| imagesize = 331x391px<br />
| noexpand = true<br />
| titletext = They didn't bring us a gift, but considering the kinetic energy of a bottle of wine at orbital speed, that's probably for the best.<br />
}}<br />
<br />
<br />
==Explanation==<br />
{{incomplete|Created by SIX ASTRONAUTS OVER YOUR HEAD RIGHT NOW - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
By exploiting ambiguities in the English language, it is possible to truthfully - if misleadingly - claim that you had the personnel of the International Space Station "over" when it passes above you.<br />
<br />
==Transcript==<br />
{{incomplete transcript}}<br />
<br />
{{comic discussion}}</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2850:_Doctor%27s_Office&diff=3279852850: Doctor's Office2023-11-05T04:51:53Z<p>Captain Video: </p>
<hr />
<div>{{comic<br />
| number = 2850<br />
| date = November 3, 2023<br />
| title = Doctor's Office<br />
| image = doctors_office_2x.png<br />
| imagesize = 740x291px<br />
| noexpand = true<br />
| titletext = "The police told me I can't be a doctor, but whenever they show up I just go into the Google Maps settings page I found and change the house to 'Police Headquarters' and then they have to do what I say."<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a NEW YORK TIMES CROSSWORD - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
In this comic, [[Beret Guy]] has discovered how to add public labels to locations on {{w|Google Maps}}. He has used the tool to label his house as a physician's office, and then proceeded to impersonate a physician, making this another comic with one of his special [[:Category:Beret Guy's Business|businesses]]. <br />
<br />
It seems that Cueball has seen and trusted the label, and has arrived for a medical consultation. He apparently is a walk-in (that is, he does not have appointment), an unheard-of situation for a physician's office in contemporary United States of America that is not an urgent-care facility (for which Beret Guy makes no claim). Thus, Cueball has bought into Beret Guy's bizarre vision, as is typical for Beret Guy comics.<br />
<br />
It is soon apparent that Beret Guy has no medical credentials. His "librarian for bones and blood" line in the first panel is nonsensical. The terms he uses while taking Cueball's temperature (second panel) are simplistic, and his prescription for Cueball's fever farcical. In the third panel, he hands Cueball what's supposed to be a medical consent form, but is in fact a ''New York Times'' crossword puzzle. The ''New York Times'' crosswords are designed to get progressively more challenging over the course of each week, but the week starts on Monday. Beret Guy's claim on this subject, at least, is accurate.<br />
<br />
In the fourth panel, Cueball finally questions whether Beret Guy's claim is accurate, and the facts of the situation are revealed - while Beret Guy wheels in a (section of a) {{w|Magnetic resonance imaging}} (MRI) device (usually a feature of a hospital or medical laboratory, not an individual physician's office, and, assembled, far larger/heavier than one person can manage on a dolly) and wonders aloud what it is for. He also comments that he bets it is loud, implying that he does not yet know and that this will be the first time he uses it. It should indeed be loud. Typically many loud noises are made, by both the actuators and from the hardware that controls and produces the magnetic fields, especially from the perspective of one laid inside the device.<br />
<br />
In the title text, the police cite Beret Guy for impersonating a physician, but Beret Guy returns to Google Maps and relabels his house "Police Headquarters", thus (by implication) making himself Chief of Police to whose authority the officers must submit - by withdrawing the "impersonating a physician" charge. If this works as claimed, it's another of the [[:Category:Strange powers of Beret Guy|strange powers of Beret Guy]], and a substantial one. However, we have only Beret Guy's word that it does. Declaring oneself a physician, in an office of one, is different from declaring oneself the appointed/elected leader of an armed force. If it does work, maybe Beret Guy's next house label is the White House. The implications are nontrivial.<br />
<br />
Beret Guy's comment that "It's a Monday, so [the crossword]'s not too hard" refers to the observation that <br />
{{w|New York Times crossword puzzles}} increase in difficulty through the week, with the easiest on Monday and hardest on Saturday (there's also a larger Sunday puzzle, but it's in {{w|The New York Times Magazine}} rather than the newspaper, and is designed to be about as hard as a Thursday puzzle).<br />
<br />
A physician imposter was also featured in [[699: Trimester]], while possibly authentic physicians behaving badly appear in [[938: T-Cells]], [[1471: Gut Fauna]], and [[1839: Doctor Visit]]. One can only hope that [[Randall]] doesn't have real-life models for these situations.<br />
<br />
==Transcript==<br />
:[Beret Guy is sitting at a desk, wearing a lab coat. Cueball is walking in from the right as Beret Guy stretches an arm out towards him in greeting.]<br />
:Beret Guy: Welcome to the doctor!<br />
:Beret Guy: We're like librarians, but for your bones and blood.<br />
<br />
:[In a frame-less panel Beret Guy is standing in front of Cueball while holding a device in his hand, which are attached with a coiling wire to a thermometer in Cueball's mouth. He reads something of the device while holding a pill bottle in the other hand.]<br />
:Beret Guy: Uh-oh! This beeper says you're too hot.<br />
:Beret Guy: You should eat some of these little snacks that make you colder.<br />
<br />
:[Zoom in on the two persons where Beret Guy is holding a pen up towards Cueball who is holding a clipboard with a newspaper page stuck to it. Cueball is looking down at the page, which has a black picture in the top left corner and lots of unreadable lines across the rest of the page.]<br />
:Beret Guy: We can make holes in you, but you have to fill out this form first.<br />
:Cueball: This is a New York Times crossword.<br />
:Beret Guy: Don't worry, it's a Monday, so it's not too hard.<br />
<br />
:[Cueball is watching as Beret Guy walks past him rolling a machine labeled "MRI" on a dolly.]<br />
:Cueball: This '''''is''''' a doctor's office, right?<br />
:Beret Guy: Yeah! It used to be my house, but I found the setting on Google Maps to change it.<br />
:Beret Guy: Hey, wanna help find out what this box does? I bet it's loud!<br />
:Label: MRI<br />
<br />
{{comic discussion}}<br />
<br />
[[Category:Comics featuring Beret Guy]]<br />
[[Category:Comics featuring Cueball]]<br />
[[Category:Beret Guy's Business]]<br />
[[Category:Strange powers of Beret Guy]]<br />
[[Category:Medicine]]</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2808:_Daytime_Firefly&diff=3198962808: Daytime Firefly2023-07-29T01:53:16Z<p>Captain Video: /* Explanation */</p>
<hr />
<div>{{comic<br />
| number = 2808<br />
| date = July 28, 2023<br />
| title = Daytime Firefly<br />
| image = daytime_firefly_2x.png<br />
| imagesize = 740x272px<br />
| noexpand = true<br />
| titletext = Mr. Jones, watch out for Ms. Lenhart! She's from genus Photuris!<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by MR. JONES. Believe in me / Help me believe in anything / 'Cause I wanna be someone who believes / Yeah / [Chorus]}}<br />
<br />
Some things are associated with being seen so much in a given context that it can be surprising to see them anywhere else. This comic starts with the initially trivial incident of a famously night-time outdoor insect, a {{w|firefly}}, being discovered indoors and during the day.<br />
<br />
This quickly becomes another typical observation, that of the experience of a schoolchild seeing someone, who they normally only encounter in the classroom, 'in the real world'. This may not be strange in small, close-knit communities, but can still be seen as extraordinary, and is sometimes an event that happens after the child (and/or teacher) has left the school and is a sign that they are now more equal citizens rather than tutor and student with vastly different lives outside of education.<br />
<br />
Unlike fireflies, teachers generally do not {{w|Bioluminesce|bioluminesce}} or flit around in the open air.{{Citation needed}} But that scenario is where the analogy quickly turns, imagining Mr Jones (the teacher) behaving like such an insect. Such an encounter would be at least as awkward as bumping into a them in a semi-social situation, and the conversation you'd be having could be terribly stilted.<br />
<br />
The title text continues the conversation with some sage advice, to the firefly-teacher, to avoid [[Miss Lenhart]], another teacher whom they believe to belong to an {{w|Photuris|aggressively mimicking genus of predatory firefly}} and thus a potential danger to his existence, as the females of that species copy the blinking mating patterns of other firefly species in order to lure in the males of those species to be eaten. The speaker is clearly concerned that Mr. Jones will be fooled by Ms. Lenhart and then cannibalized.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
<br />
{{comic discussion}}<br />
<br />
[[Category:Comics featuring Miss Lenhart]]<br />
[[Category:Comics featuring Cueball]]<br />
[[Category:Comics featuring Megan]]</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2803:_Geohydrotypography&diff=3179812803: Geohydrotypography2023-07-18T02:38:31Z<p>Captain Video: I'm so tired</p>
<hr />
<div>{{comic<br />
| number = 2803<br />
| date = July 17, 2023<br />
| title = Geohydrotypography<br />
| image = geohydrotypography_2x.png<br />
| imagesize = 339x389px<br />
| noexpand = true<br />
| titletext = The Atlantic is expanding at about 10 ppm (points per month).<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a KERNED OCEAN - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
Typing speed is typically measured in words per minute, with higher numbers indicating greater proficiency. The Atlantic Ocean is full of water. This comic suggests that, were the water covered with words, the slow widening caused by plate tectonics would increase the words per minute of whoever was typing on it by 100 words per minute.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
:If you covered the surface of the Atlantic Ocean with twelve-point printed text, with the lines wrapping at the coasts, the expansion of the ocean basin due to plate tectonics would increase your word count by about 100 words per second.<br />
<br />
:[Caption below the panel:]<br />
:My hobby: Geohydrotypography<br />
<br />
{{comic discussion}}</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2792:_Summer_Solstice&diff=3158412792: Summer Solstice2023-06-21T22:18:20Z<p>Captain Video: </p>
<hr />
<div>{{comic<br />
| number = 2792<br />
| date = June 21, 2023<br />
| title = Summer Solstice<br />
| image = summer_solstice_2x.png<br />
| imagesize = 238x373px<br />
| noexpand = true<br />
| titletext = Then I'll start work on my lunar engines to line the Moon up with the ecliptic so we can have a solar eclipse every month (with a little wobble so they're not always on the equator.)<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a SOLAR ECLIPSE ENJOYER- Please change this comment when editing this page. Do NOT look directly at the sun.}}<br />
<br />
The {{w|summer solstice}} occurs when one of Earth's poles has its maximum tilt toward the Sun. Although the summer solstice is the longest day of the year for that hemisphere, the dates of earliest sunrise and latest sunset vary by a few days. This is because Earth orbits the Sun in an ellipse, and its orbital speed varies slightly during the year.<br />
<br />
The caption says that Randall is working on a giant machine capable of adjusting the Earth's orbit. Either making it circular, or making the solstices match the days of closest or furthest distance from the Sun (perihelion or aphelion), would "fix" this so it wouldn't be so confusing.<br />
<br />
The title text discusses {{w|solar eclipses}}, which occur when the Moon is directly between the Sun and Earth. Because of the tilt of the Moon's orbit to the {{w|ecliptic}} (the plane of the Earth's orbit), most of the times when it's in between they're not in direct alignment, so the moon's shadow misses the earth and we don't get an eclipse. Randall's next project is an engine that will shift the Moon's orbit so it's not tilted so far and we get eclipses every month.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
<br />
:[Cueball, Megan and White Hat are standing. Cueball and Megan have their arms raised.]<br />
:Cueball: Happy summer solstice!<br />
:Megan: Only six days until the latest sunset of the year!<br />
:White Hat: ...Wait, what?<br />
<br />
:[Caption below the panel:]<br />
:When I finally finish building my giant engine capable of shifting the Earth's orbit, this is the first thing I'm fixing.<br />
<br />
{{comic discussion}}<br />
<br />
[[Category:Comics featuring Cueball]]<br />
[[Category:Comics featuring Megan]]<br />
[[Category:Comics featuring White Hat]]<br />
[[Category:Astronomy]]<br />
[[Category:Time]]</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2757:_Towed_Message&diff=3095412757: Towed Message2023-04-01T00:17:00Z<p>Captain Video: Link to Wikipedia</p>
<hr />
<div>{{comic<br />
| number = 2757<br />
| date = March 31, 2023<br />
| title = Towed Message<br />
| image = towed_message_2x.png<br />
| imagesize = 613x236px<br />
| noexpand = true<br />
| titletext = "Hi, what you do is fly over a designated zone and detach the--" "WE'RE SORRY, THE MOBILE CUSTOMER YOU ARE TRYING TO REACH IS OUT OF SERVICE"<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by an UNLANDABLE PLANE - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
In this comic, someone is flying a banner attached to a plane. Apparently, before they started the flight, they realized that they do not know how to land it while flying, so they decided to attach a banner allowing them to crowdsource a way to land after taking off.<br />
<br />
The phone number beginning with "{{w|555 (telephone number)|555}}" is commonly seen in movies.<br />
<br />
The title text features a caller who tries to explain the correct method (detaching the banner over a designated empty location, then landing the plane regularly), but the answering machine informs the caller that the pilots can't be reached.<br />
<br />
Notably, most such banners are created prior to takeoff. This may mean that the pilot anticipated that they would have difficulty landing and dedicated the banner to crowdsourcing a solution in flight, rather than learning how to land with a banner beforehand or even simply forgoing the banner.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
<br />
:[An airplane tows a banner. In the background, there are four small clouds and five birds]<br />
<br />
:[Text on the banner:] Do '''''you''''' know how to land a plane that's towing a banner? Call '''555-0127''' now!<br />
<br />
{{comic discussion}}<br />
<br />
[[Category:Airplane banner]]<br />
[[Category:Aviation]]</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2749:_Lymphocytes&diff=3084732749: Lymphocytes2023-03-14T01:57:32Z<p>Captain Video: </p>
<hr />
<div>{{comic<br />
| number = 2749<br />
| date = March 13, 2023<br />
| title = Lymphocytes<br />
| image = lymphocytes_2x.png<br />
| imagesize = 651x733px<br />
| noexpand = true<br />
| titletext = It's very hard to detect, but recent studies have determined that when plasma B cells are producing antibodies, they go 'pew pew pew'<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by an OLD FLASHLIGHT - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
The human body contains many different types of immune cells.{{citation needed}}<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
<br />
{{comic discussion}}</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2729:_Planet_Killer_Comet_Margarita&diff=3054352729: Planet Killer Comet Margarita2023-01-27T19:23:41Z<p>Captain Video: </p>
<hr />
<div>{{comic<br />
| number = 2729<br />
| date = January 25, 2023<br />
| title = Planet Killer Comet Margarita<br />
| image = planet_killer_comet_margarita_2x.png<br />
| imagesize = 607x942px<br />
| noexpand = true<br />
| titletext = I'll take mine on the rocks, no ice.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by 20 TRILLION LIMES - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
A {{w|margarita}} is a popular cocktail made from {{w|tequila}}, {{w|agave}}, {{w|triple sec}}, and {{w|lime juice}}. The frozen margarita variety is blended with ice, and this comic suggests making an enormous drink using the ice from a {{w|comet nucleus}} – the one depicted having more than a passing similarity to the much studied {{w|67P/Churyumov–Gerasimenko}}. Based on the amount of ice in a typical comet, it extrapolates the quantity of the other ingredients. The mixed drink is big enough to fill {{w|Lake Mead}}, a massive reservoir on the {{w|Colorado River}} created by the water held by the {{w|Hoover Dam}}.<br />
<br />
Beyond the unusual quantities and mixing method, Randall uses the general term "orange liqueur" here rather than specifying triple sec. (As of this writing, {{w|orange liqueur}} redirects to "triple sec" on Wikipedia.) Assuming that each oil tanker holds exactly the same amount of liquid, the tequila:triple sec ratio in the comic is 4:1, meaning more tequila is used than necessary (the ratio should be 5:2).<br />
<br />
''{{w|Armageddon_(1998_film)|Armageddon}}'' is a movie starring {{w|Bruce Willis}} about a team of astronauts and oil drill engineers on a mission to blow up an asteroid that's on a collision course with the Earth. The oil drill would be used to drill a hole deep into the asteroid, into which they'll drop a nuclear bomb to destroy it. The comic suggests using the same technique to explode the comet nucleus to get the ice. It should be noted that consuming any cocktail which has been infused with the radioactive byproducts commonly resulting from the detonation of a thermonuclear weapon may pose health risks which exceed those typically associated with the consumption of alcoholic beverages in general.{{Actual citation needed|It would be the relatively small primary charge that creates the radioisotopes, the thermonuclear secondary stage is practically uncontaminating beyond the initial pulse of ionising radiation and any external matter boosted by the neutron flux. To quantify the risks of alcohol vs the mean radioisotope contamination seems like a question to ask Randall to talk to his contacts about.}}<br />
<br />
In the title text, he asks for it "{{w|on the rocks}}", with no ice. In the context of cocktails this means to serve with ice. But the comet nucleus also contains lots of rocky material. If you explode the nucleus and remove the ice, the drink will be full of rocks.<br />
<br />
In the header, it says "Today's comic was drawn for Daniel Becker, based on [https://what-if.xkcd.com/162/ his winning question] submitted to the [https://xkcd.com/what-if-2/ What If? 2] contest." As explained in the What If? entry melting a comet on Earth has enough negative effects on the climate to negate the cooling effect a couple thousand times over – thus this margarita may in fact proudly wear the title "planet killer".<br />
<br />
Assuming an average oil tanker size of 25.8 million gallons, this provides approximately 1,705 servings of tequila per adult on the planet. Therefore it is a planet killer in terms of alcohol poisoning and killing off all humans of adult drinking age.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
<br />
:<big>The Planet Killer</big><br />
:Comet Ice Margarita<br />
<br />
:<u>Ingredients</u><br />
:4,000 oil tankers full of tequila<br />
:1,000 tankers full of orange liqueur<br />
:1,000 tankers full of agave<br />
:The juice from 20 trillion limes<br />
:One comet nucleus<br />
<br />
:<u>Instructions</u><br />
:(1) Drain Lake Mead, combine ingredients behind Hoover Dam<br />
:(2) Detonate comet using Bruce Willis's drilling rig from ''Armageddon'' (1998)<br />
::''Boom''<br />
:(3) Dispense drink through Hoover Dam turbines<br />
<br />
{{comic discussion}}<br />
<br />
[[Category:Puns]]<br />
[[Category:Space]]<br />
[[Category:Food]]</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2722:_Etymonline&diff=3044472722: Etymonline2023-01-09T23:27:32Z<p>Captain Video: /* Explanation */</p>
<hr />
<div>{{comic<br />
| number = 2722<br />
| date = January 9, 2023<br />
| title = Etymonline<br />
| image = etymonline_2x.png<br />
| imagesize = 458x280px<br />
| noexpand = true<br />
| titletext = NOTE TO FUTURE ETYMONLINGUISTS: Our best guess is that 'blimp' is onomatopoeia. The 'B-Limp' thing is a folk etymology.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a BLIMP - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
<br />
{{comic discussion}}</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2650:_Deepfakes&diff=2908792650: Deepfakes2022-07-27T00:19:50Z<p>Captain Video: </p>
<hr />
<div>{{comic<br />
| number = 2650<br />
| date = July 25, 2022<br />
| title = Deepfakes<br />
| image = deepfakes.png<br />
| titletext = If so great a deductive mind as Arthur Conan Doyle can be fooled by the Cottingley Deepfakes, what chance do we mortals have? Soon our very reality will be dictated by the whims of Frances (9) and Elsie (16).<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a SUBSTANDARD COPPER INGOT - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
A {{w|deepfake}} is an altered video, designed to deceive by replacing a person in a video. [[White Hat]] believes that this technology will make it difficult to trust videos. However, [[Cueball]] responds by saying that "fakes" have always existed, in photos (either through {{w|photoshopping|alterations by software such as Adobe Photoshop}}, or deliberately staging faked images, e.g. {{w|Loch Ness Monster#%22Surgeon's photograph%22 (1934)|of the Loch Ness Monster}}) and even more so by people simply lying. White Hat comes around to Cueball's position and says that even the written word is prone to deception and lying.<br />
<br />
Scientific studies of deepfakes have produced surprising results, suggesting that they are more likely to increase uncertainty than persuade,[https://journals.sagepub.com/doi/full/10.1177/2056305120903408] that their increased prevalence could inoculate the public against {{w|disinformation}},[https://dspace.cuni.cz/handle/20.500.11956/150489] and that they are more likely to be shared because of their humorousness than persuasiveness.[http://essay.utwente.nl/91654/] Other studies have found that deepfakes are persuasive, especially among those who are unfamiliar with them.[https://www.liebertpub.com/doi/abs/10.1089/cyber.2020.0174][https://www.osti.gov/biblio/1780812]<br />
<br />
The {{w|complaint tablet to Ea-nasir}} is a 3,800 year-old clay tablet containing the oldest known written complaint, in which a customer complains to a merchant, Ea-nasir, about the quality of his copper ingots. Cueball's last statement says that perhaps this complaint could have been a lie to begin with, and there was nothing wrong with Ea-nasir's wares. This supposition is arguably the humor of the comic, apart from the hyperbole of the title text.<br />
<br />
The title text references the {{w|Cottingley Fairies}}, a series of five photographs produced in 1917 by two children, Elsie Wright and Frances Griffiths, who were 16 and 9, respectively. The photographs appear to show the children playing with fairies in their garden. The photographs received widespread attention when Sir {{w|Arthur Conan Doyle}}, the author of the ''Sherlock Holmes'' stories, used the photos as proof of paranormal phenomena in a 1920 magazine article. Conan Doyle was notable for being a strong proponent of reaching conclusions based on evidence and reason, and also held a deep belief in paranormal and supernatural phenomena. In 1983, Elsie and Frances finally confessed that the photos had been faked, by the simple process of posing cardboard figures cut out of a children's book. Due to technical advances, young children now can more easily create convincingly realistic fakes, but similarly there are many more self-styled 'experts' willing and able to dedicate themselves to 'proving' one or other side of any argument about authenticity.<br />
<br />
A similar dilemma was alluded to in the [[1958: Self-Driving Issues]] comic, where technology does not create a new way to lie, but may make certain lies more convincing to some parties, such as self-driving cars in that comic.<br />
<br />
==Transcript==<br />
:[White Hat and Cueball are walking to the right.]<br />
:White Hat: Thanks to deepfakes, soon we won't know what's real anymore. Video will become meaningless.<br />
<br />
:[White Hat and Cueball walk on, Cueball lifts one hand with the palm up.]<br />
:Cueball: I dunno.<br />
:Cueball: We've had Photoshop for decades and staged photos for centuries.<br />
:Cueball: It hasn't made photos meaningless.<br />
<br />
:[Zoom in on Cueball, who is turned left towards off-panel White Hat.]<br />
:Cueball: The bottleneck for fake stuff isn't technical. The bottleneck is willingness to lie.<br />
:Cueball: "People lying" is a very old problem.<br />
:Cueball: It's a known exploit.<br />
<br />
:[Zoom back out on White Hat and Cueball who have stopped. White Hat has a hand on his chin. Cueball holds his hands out to the sides.]<br />
:White Hat: I guess technically we've been able to make '''''text''''' deepfakes for 5,000 years.<br />
:Cueball: Maybe Ea-nasir's copper ingots were actually fine!<br />
<br />
{{comic discussion}}<br />
<br />
[[Category:Comics featuring White Hat]]<br />
[[Category:Comics featuring Cueball]]<br />
[[Category:Comics featuring real people]]<br />
[[Category:Photography]]</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2643:_Cosmologist_Gift&diff=2884872643: Cosmologist Gift2022-07-09T00:33:51Z<p>Captain Video: Fix wrong number from my earlier mistake</p>
<hr />
<div>{{comic<br />
| number = 2643<br />
| date = July 8, 2022<br />
| title = Cosmologist Gift<br />
| image = cosmologist_gift.png<br />
| titletext = These neutrinos were freshly produced by a local source just 8 minutes ago<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a MUON ON SALE- Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
This comic shows a box labeled to indicate that it contains 30,000 fresh {{w|neutrino}}s and 8 zeptograms of {{w|dark matter}}. The box is intended as an inexpensive gift for a {{w|cosmologist}}. The gift giver didn't put those things in the box; both are simply passing through it. While the caption states that this would be a good gift for a cosmologist, what they or anyone else would do with such a box is uncertain.<br />
<br />
There are about a billion neutrinos per cubic meter throughout space, produced during the {{w|Big Bang}}.[https://physics.mit.edu/news/journal/physicsatmit_14_conrad/] However, the flux of "freshly produced" {{w|solar neutrino}}s at Earth is around 7&times;10<sup>10</sup>/cm<sup>2</sup>/s, yielding about 23,000 per cubic meter. <br />
<br />
Four zeptograms is a minuscule mass, equal to four sextillionths of a gram, the mass of about 200 carbon-12 atoms. Some cosmologists believe that dark matter is comprised entirely of black holes,[https://news.yale.edu/2021/12/16/black-holes-and-dark-matter-are-they-one-and-same] not omnipresent subatomic particles, in which case there is actually no dark matter at all in the box.<br />
<br />
The "local source" mentioned in the title text is the Sun; it takes light and neutrinos 8 minutes to reach Earth once they're emitted.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
<br />
:[A picture of a box with writing on one side]<br />
<br />
:Box:<br />
:30,000 neutrinos<br />
:Freshly produced<br />
:Plus 4 zeptograms of dark matter<br />
<br />
:[Caption below the panel]: <br />
:Cosmologists are easy to shop for because you can just get them a box.<br />
<br />
{{comic discussion}}<br />
[[Category:Astronomy]]</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2643:_Cosmologist_Gift&diff=2884762643: Cosmologist Gift2022-07-09T00:05:48Z<p>Captain Video: /* Transcript */</p>
<hr />
<div>{{comic<br />
| number = 2643<br />
| date = July 8, 2022<br />
| title = Cosmologist Gift<br />
| image = cosmologist_gift.png<br />
| titletext = These neutrinos were freshly produced by a local source just 8 minutes ago<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a MUON ON SALE- Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
According to this comic, "Cosmologists are easy to shop for because you can just get them a box." The example box allegedly contains 30,000 fresh neutrinos and 8 zeptograms of dark matter. The gift giver didn't put these things in the box; both are simply passing through it.<br />
<br />
Eight zeptograms is an infinitesimal amount equal to eight sextillionths of a gram. For comparison, Wolfram Alpha says it's equivalent to approximately 4800 daltons, which works out to the weight of about 400 carbon-12 atoms.<br />
<br />
The "local source" mentioned in the title text is the Sun; it takes light (and neutrinos) 8 minutes to reach Earth once they're emitted.<br />
<br />
What anyone would ''do'' with 80,000 fresh neutrinos and 8 zeptograms of dark matter is open to speculation.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
<br />
[A picture of a box with writing on one side]<br />
<br />
Box:<br />
30,000 NEUTRINOS<br />
FRESHLY PRODUCED<br />
<br />
PLUS 4 ZEPTOGRAMS<br />
OF DARK MATTER<br />
<br />
Caption: Cosmologists are easy to shop for because you can just get them a box.<br />
<br />
{{comic discussion}}</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2643:_Cosmologist_Gift&diff=2884752643: Cosmologist Gift2022-07-09T00:04:16Z<p>Captain Video: /* Explanation */</p>
<hr />
<div>{{comic<br />
| number = 2643<br />
| date = July 8, 2022<br />
| title = Cosmologist Gift<br />
| image = cosmologist_gift.png<br />
| titletext = These neutrinos were freshly produced by a local source just 8 minutes ago<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a MUON ON SALE- Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
According to this comic, "Cosmologists are easy to shop for because you can just get them a box." The example box allegedly contains 30,000 fresh neutrinos and 8 zeptograms of dark matter. The gift giver didn't put these things in the box; both are simply passing through it.<br />
<br />
Eight zeptograms is an infinitesimal amount equal to eight sextillionths of a gram. For comparison, Wolfram Alpha says it's equivalent to approximately 4800 daltons, which works out to the weight of about 400 carbon-12 atoms.<br />
<br />
The "local source" mentioned in the title text is the Sun; it takes light (and neutrinos) 8 minutes to reach Earth once they're emitted.<br />
<br />
What anyone would ''do'' with 80,000 fresh neutrinos and 8 zeptograms of dark matter is open to speculation.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
<br />
{{comic discussion}}</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2643:_Cosmologist_Gift&diff=2884742643: Cosmologist Gift2022-07-08T23:59:58Z<p>Captain Video: /* Explanation */</p>
<hr />
<div>{{comic<br />
| number = 2643<br />
| date = July 8, 2022<br />
| title = Cosmologist Gift<br />
| image = cosmologist_gift.png<br />
| titletext = These neutrinos were freshly produced by a local source just 8 minutes ago<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a MUON ON SALE- Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
According to this comic, "Cosmologists are easy to shop for because you can just get them a box." The example box allegedly contains 30,000 fresh neutrinos and 8 zeptograms of dark matter. The gift giver didn't put these things in the box; both are simply passing through it.<br />
<br />
The "local source" mentioned in the title text is the Sun; it takes light (and neutrinos) 8 minutes to reach Earth once they're emitted.<br />
<br />
What anyone would ''do'' with 80,000 fresh neutrinos and 8 zeptograms of dark matter is open to speculation.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
<br />
{{comic discussion}}</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2643:_Cosmologist_Gift&diff=2884732643: Cosmologist Gift2022-07-08T23:59:42Z<p>Captain Video: /* Explanation */</p>
<hr />
<div>{{comic<br />
| number = 2643<br />
| date = July 8, 2022<br />
| title = Cosmologist Gift<br />
| image = cosmologist_gift.png<br />
| titletext = These neutrinos were freshly produced by a local source just 8 minutes ago<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a MUON ON SALE- Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
According to this comic, "Cosmologists are easy to shop for because you can just get them a box." The example box allegedly contains 30,000 fresh neutrinos and 8 zeptograms of dark matter. The gift giver didn't put these things in the box; both are simply passing through it.<br />
<br />
The "local source" mentioned in the title text is the Sun; it takes light (and neutrinos) 8 minutes to reach Earth once they're emitted.<br />
<br />
What anyone would *do* with 0,000 fresh neutrinos and 8 zeptograms of dark matter is open to speculation.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
<br />
{{comic discussion}}</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2626:_d65536&diff=2848382626: d655362022-06-01T04:10:01Z<p>Captain Video: /* Explanation */ A little shorter</p>
<hr />
<div>{{comic<br />
| number = 2626<br />
| date = May 30, 2022<br />
| title = d65536<br />
| image = d65536.png<br />
| titletext = They're robust against quantum attacks because it's hard to make a quantum system that large.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a HEXAKISMYRIAPENTAKISCHILIAPENTAHECTATRIACONTAKAIHEXAHEDRON - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
In binary computing, 16 bit numbers range from 0 to 65535, for a total of 65536 unique numbers, a number which is hence well-known to software engineers. Generating large numbers in a manner that is truly random is a recurring problem in cryptography, required to send private messages to another party. People today still use dierolls to generate private random numbers.<br />
<br />
In role-playing games (and occasionally in other tabletop games), dice are often referred to as d''n'' according to their number of faces. A traditional six-faced die would be a d6, and many popular pen-and-paper role-playing games use dice ranging between d4 and d20. While there are larger dice used in tabletop games (most commonly d100), these are usually split into multiple smaller ones to save the hassle of throwing large dice. For example, a d100 is often two d10s rolled together, with one die providing the first digit and the other die giving the second digit — the total number of possible combinations (100) is the product of the number of faces of the two dice (10 * 10). There are, however, "real" {{w|Zocchihedron|d100s}} and similar dice as well, but they are considered specialty dice and often nicknamed "golf balls" to emphasize how large and unwieldy they are. The Zocchihedron (d100) die is also biased because of geometry requiring different sized faces, the next unbiased die is a d120, it is very likely that Cueball's d65536 die is also biased.<br />
<br />
Here, Cueball has constructed a d65536 for generating random 16 bit numbers, likely with a [https://www.shapeways.com/product/U9CN6MT6X/d256 3d printer] or other CAM tools. It may have solved the problem of generating large random numbers with fewer die rolls, but presents a new set of challenges from its sheer size, dwarfing an average human. While large in itself, a die that big could still be emulated by rolling multiple dice (e.g. 8 4-faced dice or 16 coin flips) and converting the result into binary before getting the desired number. Part of the humor stems from the the comic completely failing to mention another big problem with this die: Deciding which of the 65536 faces is up. This is another problem with a d100, as many sides appear to be up at once. Similarly horrible hilarity will ensue if such a massive die is cast with enough energy to be random while expect it to stop rolling in a short period of time let alone on a table top or even within a building (which raises the question of whether breaking through a wall or furniture is all part of the randomization or requiring a re-roll as per house rules). <br />
<br />
The closest regular shape similar to the depicted in the comic could be a {{w|Goldberg polyhedron}}. However, no such polyhedron exists with exactly 65536 hexagonal faces. The closest Goldberg Polyhedron has a mixture of 65520 hexagons and 12 pentagons, totaling 65532 faces. It is possible to construct a fair die without a matching regular shape by limiting the sides which it could land on and designing those sides to be fair (for instance, a prism with rectangular facets that extend its entire length, and rounded ends to ensure it doesn't balance on end).<br />
<br />
The title text references how many cryptographic systems (especially RSA and other factoring-is-hard based systems) are vulnerable to quantum attacks as quantum computing technology develops. The title text is essentially punning on the idea of a "large" quantum system. "Large" in the quantum computing sense would be on the order of 64 qubits each of which would be an atom or two at most. This would still be microscopic and will never be as large as the giant die the comic is centered on; but for a well-observed environment and human rolling without sufficient entropy (consider somebody obsessed with a certain number dropping the die on something soft), a conventional computer could predict some rolls. See also [[538]] for non-mathematical paths of cryptography.<br />
<br />
==Trivia==<br />
*If a real d65536 were constructed with each number having an equal area and each printed in 12 point font, the resulting die would be about 5 feet (1.5 meters) in diameter, which isn't several times the size of a person as the comic suggests, but is still large enough to be hilariously inconvenient. If it were made out of standard acrylic, and not hollow, it would weigh about 2 tons (1700kg).<br />
*This die would have a 0.00001526 chance of rolling a natural one (or any other number).<br />
*There are seven 16-bit numbers fully visible in the picture: 30827, 25444, 11875, 28525, 12082, 13874 and 13359. They conceal a message. If these numbers are split big-endian into two 8-bit ASCII characters each, the result is <code>xkcd.com/2624/</code>.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
:[Drawing of a large die with many sides, about ten meters in diameter; Cueball is standing next to it as a size reference. A small portion of the die's surface is zoomed in, showing elongated hexagonal faces with five-digit numbers.]<br />
<br />
:[Numbers on the zoomed in part of the die, "..." represents being cut off:] <br />
:30827 <br />
:16[bottom part of a line][small circle] <br />
:...38 <br />
:11875 <br />
:25444 <br />
:...[top part of a line]5 <br />
:12082 <br />
:28525 <br />
:3... <br />
:13359 <br />
:13874 <br />
:2...<br />
<br />
:[Caption below the image:]<br />
:The hardest part of securely generating random 16-bit numbers is rolling the d65536.<br />
<br />
{{comic discussion}}<br />
<br />
[[Category:Cryptography]]<br />
[[Category:Comics featuring Cueball]]</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2623:_Goofs&diff=2767422623: Goofs2022-05-24T00:36:08Z<p>Captain Video: /* Explanation */</p>
<hr />
<div>{{comic<br />
| number = 2623<br />
| date = May 23, 2022<br />
| title = Goofs<br />
| image = goofs.png<br />
| titletext = The film is set in 2018, but when Commander Bremberly chases the hologram through Times Square, there's a billboard for Avengers: Age of Ultron. Depending on the date, that billboard would have been advertising either Infinity War or this movie.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a WILLING SUSPENSION OF DISBELIEF- Please change this comment when editing this page. Do NOT think about how much of this stuff applies to Explain xkcd.}}<br />
IMDb is the {{w|Internet Movie Database}}, a website that contains detailed information about movies and TV shows. One of the sections in many entries is "Goofs". This may list bloopers, inconsistencies, implausible actions, anachronisms, etc. in the movie. The comic makes fun of this with several goofs that simply point out differences between something in the movie and reality; but since the movie is fiction (in this case, a science fiction film that includes a space detective, a cybernetic dog, blimp drones, and a hologram kissing scene), it's not expected to exactly mirror reality.<br />
<br />
In the first goof, the street doesn't actually exist in the city in which the movie is set. Unless the address is important to the plot (Manhattan has a number of streets with well-known characters, e.g. the main theatre district is on Broadway, Fifth Avenue is a major shopping district, and Wall Street is known for large financial institutions), screenwriters often just make up street names and it might actually be expedient to 'rename' a setting in many cases, to avoid the actual collision of fictional and actual setting such as having {{w|A_Nightmare_on_Elm_Street|"A Nightmare On <Your Streetname>"}}.<br />
<br />
In the second example, they point out that there's no real harpoon store at the location where the characters obtain a harpoon in the movie, and the nearest actual harpoon store doesn't have a display window like the one in the movie. Movies usually take liberties with details like this for plot expediency, it's not considered a goof. Manhattan does not appear to have ''any'' notable harpoon stores,{{Citation needed}} with or without the kind of frontage described. <!-- Note that the 'goof in the goof list' goes better in the #Goofs section, but we can still have a bit of fun here, right? ;) --><br />
<br />
In the third example, the background of a scene is of an apartment in Downtown Vancouver (a cheap and popular filming location that frequently stands in for other cities). The goof points out that the real-life apartment does not belong to the character who supposedly lives in it. Most movie characters do not exist in reality{{citation needed}}, and many scenes are set in fictional locations that are completely separate from their real-life filming locations. As such, this is only a "goof" if the scene is taken entirely literally.<br />
<br />
The title text describes an actual anachronism. The film is set in 2018, but there's a billboard for the movie ''{{w|Avengers: Age of Ultron}}''. That movie came out in 2015, while the next Avengers film, ''{{w|Avengers: Infinity War}}'', came out in 2018. Assuming the movie was filmed before 2018, the filmmakers wouldn't have known what films would be current at the time it would be released, and certainly not the artwork they'd be using to promote them. They could have chosen to set it 3 years earlier, but again, unless the specific date is significant to the plot, it's common to set a film at about the same time it's released but with a bare minimum of fakery by trying not to show ''unimportant'' newspaper dates, etc, so that set-dressing and props-department budgets aren't excessive. Generic advertisements for fictional (or {{w|Last Action Hero|parody}}) films might be put over egregiously obvious existing material, physically or in post-production editing, as might references to major brands – perhaps replaced by those agreed with from {{w|product placement}} partners.<br />
<br />
The title text also mentions the possibility of a self-reference – the billboard could be for this film itself since it's being released at the same time it's set. This assertion that {{w|Blazing Saddles|in-universe self-reference}} is plausible for a movie production is likely another example of the goof's writer failing to understand the basic "premise of fiction". Most movies do not exist within the fictional world they portray, and many audiences would find self-reference to be a far greater obstacle to suspending disbelief than an ad for the wrong Avengers movie.<br />
<br />
===Goofs===<br />
There is no entry for a film featuring an agent Glennifer on IMDB. Randall is clearly failing to do basic research.<br />
<br />
On the real IMDb, each item in the Goofs section would be listed under a category such as "Errors in geography" (which might apply to the three goofs listed in the main cartoon) or "Anachronisms" (which might apply to the goof in the title text). However, no such category is displayed here.<br />
<br />
On real Goofs pages, the information below each entry includes a public feedback listing (X of Y found this interesting) and a link entitled "Share this". In the comic, only unintelligible squiggles are included in their place, which really breaks the immersion of the purported "webpage". Of course, on a real IMDb page, all of the text would also be in the Verdana font, not Randall's handwriting.<br />
<br />
The comic features two entries with a yellow background, which is impossible. On IMDb, entries alternate between having white and gray backgrounds and only turn yellow when the mouse hovers over them.<br />
<br />
On IMDb, the number of goofs is located in a navigation box between the header and the goofs list. In the comic, the number is placed in the header, and there is no navigation box at all.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
<br />
:[An excerpt from an Internet Movie Database web page showing a list of goofs from a film. Each item has some small illegible text below it, which on the real IMDb would say something like "7 of 72 found this interesting | Share this". The first and third items have a faint yellow-tinted background. The third item is only partially visible at the bottom of the "screen".]<br />
:[Heading:]<br />
:'''Goofs (78)'''<br />
:[List:]<br />
:The space detective's office is on Chestnut Ave, but Lower Manhattan has no street by that name. Agent Glennifer pursues the cybernetic dog onto what is clearly Ludlow Street.<br />
:The agents destroy the blimp drones in Union Square with harpoons from a store display rack. The nearest harpoon store is several blocks away and has no outdoor displays.<br />
:The apartment in the background of the hologram kissing scene actually exists in downtown Vancouver. We called the owners, who confirmed they had no residents named [...]<br />
<br />
:[Caption below the panel:]<br />
:Sometimes the IMDB "Goofs" section really seems to struggle with the whole premise of fiction.<br />
<br />
{{comic discussion}}<br />
<br />
[[Category:Comics with color]]</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2618:_Selection_Bias&diff=2686722618: Selection Bias2022-05-11T21:35:53Z<p>Captain Video: /* Explanation */</p>
<hr />
<div>{{comic<br />
| number = 2618<br />
| date = May 11, 2022<br />
| title = Selection Bias<br />
| image = selection_bias.png<br />
| titletext = We carefully sampled the general population and found that most people are familiar with acquiescence bias.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a STATISTICS CONFERENCE - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
Blondie speaks to a crowd at "Statistics Conference 2022" and, by show of hands, learns that most of the audience is familiar with {{w|selection bias}}. The joke is that she's falling for the very thing she's trying to explain. A statistics conference is likely to have a much higher percentage of statisticians in the audience than a truly random sample of the population would, and therefore be familiar with this statistical term, which describes exactly that phenomenon.<br />
<br />
This joke also ties into how statistics as a whole can be highly counter-intuitive and sometimes almost paradoxical, where things like the {{w|Monty Hall problem}} and {{w|survivorship bias}} lead people into thinking the answer to a problem is definitely in a place it's not. That Blondie, presumably a statistician herself, made this kind of mistake is professionally embarrassing but not unprecedented.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
[Blondie is standing at a lectern, under a sign reading “Statistics conference 2022”. In front of her are two Cueballs, Hairbun, and Megan, all seated and raising their hands.]<br />
<br />
Blondie: Raise your hand if you’re familiar with selection bias. <br />
<br />
Blondie: As you can see, it’s a term most people know... <br />
<br />
{{comic discussion}}<br />
<br />
[[Category:Comics featuring Blondie]]<br />
[[Category:Comics featuring Cueball]]<br />
[[Category:Comics featuring Hairbun]]<br />
[[Category:Comics featuring Megan]]<br />
[[Category:Public speaking]]</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2616:_Deep_End&diff=2650102616: Deep End2022-05-07T21:18:59Z<p>Captain Video: </p>
<hr />
<div>{{comic<br />
| number = 2616<br />
| date = May 6, 2022<br />
| title = Deep End<br />
| image = deep_end.png<br />
| titletext = Hey! No running in the back-arc basin!<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|This article needs additional citations for verification. Unsourced articles may be given an espresso and a free lolcat. The transcript also needs reformatting. - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
Pools, like oceans, contain water. This comic produces a schematic for the former, derived from science about the latter. On Earth, the surface consists of tectonic plates which move around. In this comic, [[Randall]] equates swimming pools with {{w|plate tectonics}}, to explain how deep ends form in said pools. Unfortunately,<sup>&#91;[[285: Wikipedian Protester|''clarification needed'']]&#93;</sup> swimming pools aren't really formed by plate tectonics.{{Citation needed}}<br />
<br />
A {{w|swimming pool}} is a pool of water, typically used for swimming. Most of these have a deep end and a shallow end. This is intentional, usually to accommodate for new swimmers to have somewhere to stand while accommodating for more confident swimmers for whom the floor would get in the way.<br />
<br />
{{w|Subduction}}, a geological process in which one plate slips beneath another and is forced down into the mantle, is shown here as the reason swimming pools have deep ends. This usually takes place between continental plates and oceanic plates, although it could happen with two oceanic plates. The comic depicts the former; an oceanic plate subducting under a continental one.<br />
<br />
A splash zone is an area of a waterpark with water being sprayed around, allowing people to get wet without the need to get into the pool. In this comic, the splash zone is actually geysers, fed by the bubbles of water from the subduction. While this particular scenario as shown in the comic is obviously far-fetched, subduction zones do create similar effects: water moving up from subducting plates is the origin of many {{W|volcanic arc|volcanic arcs}}. These volcanic systems sometimes include features such as the geysers depicted in the comic's splash zone.<br />
<br />
The title text refers to {{W|back-arc basin|back-arc basins}}, zones of depression that sometimes occur slightly beyond volcanic arcs due to a rift in the tectonic plate. The ban on running in this area likely has more to do with its proximity to the pool area than any danger intrinsic to back-arc basins. A typical safety rule around swimming pools is to avoid running on the pool deck to prevent injuries due to slipping and falling on the hard deck.<br />
<br />
Other comics that mention unusual tectonic plate motion include [[1388: Subduction License]] and [[1874: Geologic Faults]].<br />
<br />
==Transcript==<br />
<br />
{{incomplete transcript}}<br />
On the left of the image is the shallowest water in the pool, about the height of [[Megan]], excluding her head. Going to the right from there, the pool floor (Representing the oceanic plate) begins to curve downwards towards the subduction zone. As the floor goes down, the water gets deeper. In the deepest area, it is labeled "Deep End".<br />
<br />
At the bottom of the deep end, there is a curve and a deposit on the plate/pool floor. This is likely sediment buildup from waterborne debris that has settled there. Within the sediment, there are some small interstitial pools of trapped water within. An arrow upon the subducting material indicates that the oceanic plate is moving left-to-right across the image. Some of the water is dragged along by the oceanic plate, while others float up through the continental plate until they reach the "Splash zone". Several children (small versions of [[Ponytail]], [[Hairy]], and an unidentifiable character) are seen frolicking in the splash zone, as would normally be expected.<br />
<br />
To the left of the splash zone is an area labelled the "Pool deck", above which a [[Cueball]] figure is jumping off the diving board.<br />
<br />
{{comic discussion}}<br />
<br />
[[Category:Comics featuring Cueball]]<br />
[[Category:Geology]]</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2616:_Deep_End&diff=2649532616: Deep End2022-05-07T02:24:53Z<p>Captain Video: /* Explanation */</p>
<hr />
<div>{{comic<br />
| number = 2616<br />
| date = May 6, 2022<br />
| title = Deep end<br />
| image = deep_end.png<br />
| titletext = Hey! No running in the back-arc basin!<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by X.K.C.D(renewed) - I don't know how to get this to work, but I beat the bot to making it! Please add the explanation - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
Pools, like oceans, contain water. This comic produces a schematic for the former, derived from science about the latter. On Earth, the surface consists of tectonic plates which move around. In this comic, [[Randall]] equates Swimming pools with {{w|plate tectonics}}, to explain how deep ends form in said pools. Unfortunately, swimming pools aren't really formed by plate tectonics{{Citation needed}}.<br />
<br />
A {{w|swimming pool}} is a pool, typically used for swimming {{Citation needed}}. Most of these have a deep end and a shallow end. This is intentional, likely to accomadate for new swimmers to have somewhere to stand while accommodating for more confident swimmers for whom the floor would get in the way{{Actual citation needed}}.<br />
<br />
{{w|Subduction}}, a geological process in which one plate slips beneath another and is forced down into the mantle, is shown here as the reason swimming pools have deep ends. This usually takes place between continental plates and oceanic plates, although it could happen with two oceanic plates. The comic depicts the former: an oceanic plate subducting under a continental one.<br />
<br />
On the left image, there is the shallow end. The water is the shallow end is the shallowest in the pool, about the height of [[Megan]], excluding her head. Going right from there, the pool floor (Representing the oceanic plate) begins to curve downwards towards the subduction zone. As the floor goes down, the water gets deeper{{Citation needed}}. In the deepest area, it is labeled "Deep End"<br />
<br />
At the bottom of the deep end, there is a curve and a deposit on the plate/pool floor. This is likely sediment buildup from waterborne debris that has settled there.<br />
<br />
==Transcript==<br />
{{incomplete transcript}}<br />
<br />
{{comic discussion}}<br />
<br />
[[Category:Comics featuring Cueball]]<br />
[[Category:Comics]]</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2614:_2&diff=2319212614: 22022-05-02T22:57:26Z<p>Captain Video: /* Explanation */</p>
<hr />
<div>{{comic<br />
| number = 2614<br />
| date = May 2, 2022<br />
| title = 2<br />
| image = 2.png<br />
| titletext = It's like sigma summation notation, except instead of summing the argument over all values of i, you 2 the argument over all values of 2.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a 2 - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
2 is a number.{{citation needed}}<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
<br />
{{comic discussion}}</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2605:_Taylor_Series&diff=2301132605: Taylor Series2022-04-11T17:56:32Z<p>Captain Video: </p>
<hr />
<div>{{comic<br />
| number = 2605<br />
| date = April 11, 2022<br />
| title = Taylor Series<br />
| image = taylor_series.png<br />
| titletext = The Taylor series should have been canceled after the first term.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a BOT - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
In mathematics, the {{w|Taylor series}} of a function is an infinite sum of terms that are expressed in terms of the function's derivatives at a single point. So the equation would never end. Which is indeed, good news.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
<br />
{{comic discussion}}</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2602:_Linguistics_Degree&diff=2297852602: Linguistics Degree2022-04-06T04:12:21Z<p>Captain Video: /* Explanation */</p>
<hr />
<div>{{comic<br />
| number = 2602<br />
| date = April 5, 2022<br />
| title = Linguistics Degree<br />
| image = linguistics_degree.png<br />
| titletext = You'd think 'linguistics' would go to someone important in the field, but it's actually assigned to a random student in Ohio who barely graduated and then went into automotive marketing.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a JACKALOPE SLURPING UP A BASSOON - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
[[Hairbun]] hands [[Megan]] a linguistics degree, and informs her she now "in charge of" the word '{{wiktionary|bassoon}}.' Watching this, Ponytail and Cueball compare the words they were assigned when ''they'' got their linguistics degrees, '{{wiktionary|jackalope}}' and '{{wiktionary|slurp}}' respectively.<br />
<br />
It is never clarified what being "in charge of" a word entails. It could mean being in charge of keeping track of the word, or having actual authority over the use of the word, which is unlikely as normally [[1726|language use cannot be dictated by a single person]]. Also, no specific university has control over all of linguistics as far as we know, so it would require every university capable of giving people linguistics degrees to co-operate, so nobody is assigned the same word.<br />
<br />
The title text merely furthers how seemingly random the entire situation is. The word "linguistics" was assigned to a "random student in Ohio who barely graduated and then went into automotive marketing", who we can assume isn't very important to the field of linguistics.{{Citation needed}} The rationale for this is not expounded and may not exist.<br />
<br />
==Transcript==<br />
:[Hairbun and Megan, who is wearing a graduation cap, are standing on a platform with Ponytail and Cueball standing below. Hairbun is handing a roll to Megan.]<br />
:Hairbun: Congratulations on the degree! Your word is "Bassoon."<br />
:Ponytail: Oh nice! Not as cool as my "Jackalope," but still not bad.<br />
:Cueball: You all are lucky. I'm stuck with "Slurp."<br />
:[Caption below panel:]<br />
:Every linguistics degree comes with one word that you're put in charge of.<br />
<br />
{{comic discussion}}<br />
[[Category:Language]]<br />
[[Category:Comics featuring Hairbun]]<br />
[[Category:Comics featuring Megan]]<br />
[[Category:Comics featuring Ponytail]]<br />
[[Category:Comics featuring Cueball]]</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2598:_Graphic_Designers&diff=2290522598: Graphic Designers2022-03-26T02:51:05Z<p>Captain Video: </p>
<hr />
<div>{{comic<br />
| number = 2598<br />
| date = March 25, 2022<br />
| title = Graphic Designers<br />
| image = graphic_designers.png<br />
| titletext = They might make it past that first line of defense. For the second, you'll need some picture frames, a level, and a protractor that can do increments of less than a degree.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by HEX CODE #D3D3D3 AND FRIENDS - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
Cueball is inviting a friend into his freshly repainted residence. The friend is presumably a graphic designer (per the caption) and doesn't want to enter. The caption analogizes this with a specific bit of vampire lore: Vampires can only enter a house if welcomed in by the owner.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
<br />
{{comic discussion}}</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2595:_Advanced_Techniques&diff=2288352595: Advanced Techniques2022-03-22T18:24:35Z<p>Captain Video: /* Explanation */ Copy edit</p>
<hr />
<div>{{comic<br />
| number = 2595<br />
| date = March 18, 2022<br />
| title = Advanced Techniques<br />
| image = advanced_techniques.png<br />
| titletext = A blow from Emmy's Cutlass of Variations will transport the dragon to a corresponding symmetric position in the Noetherworld.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by AN EULISH CLAUSS- Please slay the CORRECT dragon when editing this page. Do NOT travel to the Noetherworld. Do NOT pass Go. Please collect the correct sedenion.}}<br />
In typical [[Miss Lenhart]] fashion, she is teaching a mathematics class where she outlines a process by which a mathematical result is achieved through steps which sound suspiciously like magical {{w|Role-playing game|RPG}} logic. She both includes dragons and arrows to slay it.<br />
<br />
One of her students asks if this is a metaphor for the technique, but her rather tetchy reply "Does this look like English class?!" seems to imply that she literally means that dragons and arrows will be employed in the resolution of the problem. It is also clear from the slide she is pointing at that she has drawn a dragon and a man with a bow that is aiming an arrow at the dragon. Whilst metaphor is an important part of many languages, and so is definitely taught in language classes, it is not usually used in math classes.<br />
<br />
The caption beneath the comic states that this approach describes "All advanced math techniques." This could be a reference to the now-common approach in higher mathematics in which a problem is transformed into another domain where it is easier to solve, then transformed back. For instance, in {{w|Fourier analysis}}, commonly used for analyzing the behavior of signals or dynamical systems, a problem can be transformed from the time domain to the frequency domain, solved, and then transformed back again. A (much) more complex example is Andrew {{w|Wiles's proof of Fermat's Last Theorem}}, which uses {{w|modularity theorem|modularity lifting}} to transform the problem. Here Miss Lenhart says she will transform a math problem into an actual dragon, slay it, and transform the corpse back into mathematics.<br />
<br />
An alternative view is that Randall is referring to {{w|Arthur C. Clarke}}'s {{W|Clarke's three laws|third law}} that ''Any sufficiently advanced technology is indistinguishable from magic'', as re-framed for mathematics. What [[Randall]] would be implying is that all advanced math techniques look like magic to non-mathematicians. (Another advanced and somewhat magical math technique is deployed by Miss Lenhart in [[1724: Proofs]].)<br />
<br />
Invocations are a common classification for spoken or vocalized types of spell. In the logic Miss Lenhart used, 'invoking' Gauss's operator may refer to casting a magical spell with verbal components (such as [https://roll20.net/compendium/dnd5e/True%20Polymorph True Polymorph]). The operator is presumably named after the famous German mathematician {{w|Carl Friedrich Gauss}}. There is nothing on Wikipedia called Gauss's operator, but there is both {{w|Gauss's law}} and the {{w|Gauss–Kuzmin–Wirsing operator}}. As neither can transform an equation into a dragon, it's clear Randall is making a joke.<br />
<br />
Slaying the dragon with Hilbert's arrow indicates that the arrow has some magical properties. The arrow is presumably named after {{w|David Hilbert}}, known for many mathematical developments including {{w|Hilbert's problems}} and {{w|Hilbert spaces}}. A Hilbert space converts subsets of an infinite vector space into a complete metric space, allowing the use of linear algebra and calculus methods which might otherwise be applicable only to finite Euclidean spaces. Vectors could be compared with an arrow. Magical arrows are frequently used to slay dragons in myth and role-playing games. Magical items in RPGs such as {{w|Dungeons & Dragons}} are often named after a creator or famous user; hence, a magical "Arrow of Hilbert" might traverse infinite spaces or affect targets for which one or more stats are effectively infinite.<br />
<br />
There is in fact a class of {{w|Dragon curve}}s, which do have the sort of S-shape shown on the whiteboard, but they have no connection to Gauss's operator, and are not actual dragons that need slaying.<br />
<br />
The title text contains two puns and a reference. The phrase "{{w|Cutlass}} of Variations" is a pun on the mathematical technique called "{{w|Calculus of variations}}". The word "Noetherworld" is a pun on "{{w|underworld|netherworld}}". The reference is to the mathematician {{w|Emmy Noether}}, a giant in the field of abstract algebra. Furthermore, {{w|Noether's Theorem}} is used in the Calculus of Variations. She was previously referenced as one of many important women in science back in [[896: Marie Curie]].<br />
<br />
==Transcript==<br />
:[Miss Lenhart is using a stick to point at a whiteboard behind her while facing, presumably, a crowd of off-panel students. The white board has a drawing of a snake-shaped dragon with wings, flying with it's body in an S-shape. An archer is pointing an arrow up at the dragon above him. Above the drawings there are three and below two rows of unreadable text and equations.]<br />
:Miss Lenhart: To solve this equation, we invoke Gauss's operator to transform it into a dragon. <br />
:Miss Lenhart: Then we slay the dragon with Hilbert's Arrow, and transform its corpse back into the solution.<br />
:Off-panel voice: Just to be clear, this is a metaphor, right?<br />
:Miss Lenhart: Does this '''''look''''' like English class?!<br />
<br />
:[Caption below the panel:]<br />
:All advanced math techniques<br />
<br />
{{comic discussion}}<br />
<br />
[[Category:Comics featuring Miss Lenhart]]<br />
[[Category:Math]]</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2595:_Advanced_Techniques&diff=2286322595: Advanced Techniques2022-03-19T05:44:14Z<p>Captain Video: Put back in explanation line I took out by mistake</p>
<hr />
<div>{{comic<br />
| number = 2595<br />
| date = March 18, 2022<br />
| title = Advanced Techniques<br />
| image = advanced_techniques.png<br />
| titletext = A blow from Emmy's Cutlass of Variations will transport the dragon to a corresponding symmetric position in the Noetherworld.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by AN ENGLISH CLASS- Please slay this dragon when editing this page. Do NOT travel to the Noetherworld.}}<br />
<br />
Blondie is teaching a class. She outlines a process by which a mathematical result is achieved through what sounds suspiciously like witchcraft. The caption describes this scenario as being "All advanced math techniques."<br />
<br />
This comic plays on mathematical terms which have other meanings, using them in different contexts from the ones intended for the terms. <br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
:[ [[Miss Lenhart]] is using a stick to point at a whiteboard with a drawing of a dragon, an archer and rows of text on it, while facing, presumably, a crowd of students.]<br />
:Miss Lenhart: To solve this equation, we invoke Gauss's operator to transform it into a dragon. <br />
:Miss Lenhart: Then we slay the dragon with Hilbert's Arrow, and transform its corpse back into the solution.<br />
:Voice off-screen: Just to be clear, this is a metaphor, right?<br />
:Miss Lenhart: Does this '''look''' like English class?!<br />
<br />
:[Caption below the panel]:<br />
:All advanced math techniques<br />
<br />
{{comic discussion}}<br />
[[Category:Comics featuring Miss Lenhart]]<br />
[[Category:Math]]</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2595:_Advanced_Techniques&diff=2286312595: Advanced Techniques2022-03-19T05:43:16Z<p>Captain Video: /* Explanation */</p>
<hr />
<div>{{comic<br />
| number = 2595<br />
| date = March 18, 2022<br />
| title = Advanced Techniques<br />
| image = advanced_techniques.png<br />
| titletext = A blow from Emmy's Cutlass of Variations will transport the dragon to a corresponding symmetric position in the Noetherworld.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by AN ENGLISH CLASS- Please slay this dragon when editing this page. Do NOT travel to the Noetherworld.}}<br />
<br />
Blondie is teaching a class. She outlines a process by which a mathematical result is achieved through what sounds suspiciously like witchcraft. The caption describes this scenario as being "All advanced math techniques."<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
:[ [[Miss Lenhart]] is using a stick to point at a whiteboard with a drawing of a dragon, an archer and rows of text on it, while facing, presumably, a crowd of students.]<br />
:Miss Lenhart: To solve this equation, we invoke Gauss's operator to transform it into a dragon. <br />
:Miss Lenhart: Then we slay the dragon with Hilbert's Arrow, and transform its corpse back into the solution.<br />
:Voice off-screen: Just to be clear, this is a metaphor, right?<br />
:Miss Lenhart: Does this '''look''' like English class?!<br />
<br />
:[Caption below the panel]:<br />
:All advanced math techniques<br />
<br />
{{comic discussion}}<br />
[[Category:Comics featuring Miss Lenhart]]<br />
[[Category:Math]]</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2591:_Qua&diff=2282232591: Qua2022-03-10T02:33:43Z<p>Captain Video: </p>
<hr />
<div>{{comic<br />
| number = 2591<br />
| date = March 9, 2022<br />
| title = Qua<br />
| image = qua.png<br />
| titletext = Qua qua qua is the sine qua non of sine qua non qua sine qua non.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by THREE FIFTHS OF A DUCK - Please expand the explanation, and clarify the definition of "qua". Do NOT delete this tag too soon.}}<br />
[[wikt:qua|Qua]] is a rare formal word, from Latin, roughly meaning "as". Saying something is "X qua X" (e.g. "entertainment qua entertainment") means X is being used for its real purpose and its own sake.<!-- I dunno, probably just one or the other --> [[Cueball]] claims that people only use ''qua'' to "sound pretentious" without properly understanding its meaning. Thus, people do not use "qua ''qua'' qua", or "qua for the sake of qua". However, [[Megan]] one-ups this with a series of seven ''qua''s: she compliments Cueball's successful use of "qua qua qua ''qua'' qua qua qua", or "the phrase 'qua qua qua' for its correct meaning".<br />
<br />
The joke is that, for the reader, the conversation has likely dissolved into gibberish because of unfamiliar terminology and {{w|semantic satiation}}. This is similar to other complex sentences involving {{w|Buffalo buffalo|"buffalo"}}, {{w|That that is is that that is not is not is that it it is|"that" and "is"}}, and {{w|Had had had|"had"}}. Following this trend, you can create a grammatically correct sentence that includes 'qua' a consecutive number of times equal to (2<sup>n</sup>-1), where n is a positive integer.<br />
<br />
The title text goes further with this, using the specific Latin phrase {{w|sine qua non}}, meaning literally "without which not" and commonly "absolutely necessary" or "essential". Thus, the title text says that "the word 'qua' in its real meaning is essential to the phrase 'sine qua non' used correctly".<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
:[Cueball and Megan are speaking to each other in a single panel.]<br />
:Cueball: People mostly use "qua" to sound pretentious. You rarely hear qua ''qua'' qua.<br />
:Megan: Nice use of qua qua qua ''qua'' qua qua qua.<br />
<br />
{{comic discussion}}<br />
[[Category:Comics featuring Cueball]]<br />
[[Category:Comics featuring Megan]]<br />
[[Category:Language]]</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2586:_Greek_Letters&diff=2275622586: Greek Letters2022-02-26T02:28:24Z<p>Captain Video: /* Explanation */</p>
<hr />
<div>{{comic<br />
| number = 2586<br />
| date = February 25, 2022<br />
| title = Greek Letters<br />
| image = greek_letters.png<br />
| titletext = If you ever see someone using a capital xi in an equation, just observe them quietly to learn as much as you can before they return to their home planet.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by '''''O R B S''''' PRO®- Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
Mathematics uses lots of Greek letters, [https://en.wikipedia.org/wiki/Greek_letters_used_in_mathematics,_science,_and_engineering typically using the same letter consistently to represent a particular constant or type of variable]. <br />
This comic gives a (non-)explanation of what they typically mean.<br />
<br />
The letters are:<br />
<br />
- lower-case pi<br />
<br />
Typically used to refer to the constant ratio between a circle’s circumference and its diameter (approximately 3.14). This usage of pi commonly applies to equations in introductory geometry classes, which would be considered "simple" by advanced mathematicians. However there are several advanced (facetiously, "impossible") equations which also use pi to represent different variables, see: [https://en.wikipedia.org/wiki/Pi_(letter)#Lowercase_Pi Pi (letter) - Wikipedia]<br />
<br />
- capital delta<br />
<br />
Typically used to refer to a change in quantity.<br />
<br />
- lower-case delta<br />
<br />
Also typically used to refer to a change in quantity, but unlike the capital delta, this is only for infinitesimal changes and is used in derivative and integration expressions in mathematics hence the text's reference to "a mathematician's fault".<br />
<br />
- lower-case theta<br />
<br />
Typically used to refer to an angle, and is notably used in the polar coordinate system. The text refers to its close relationship with circles, on which the polar coordinate system is based on.<br />
<br />
- lower-case phi<br />
<br />
Typically used to refer to another angle other than one referred to by theta. It's used in spherical coordinates, and the text refers to how spheres, or orbs, are important in spherical coordinates. <br />
<br />
- lower-case epsilon<br />
<br />
Typically used to refer to very small quantities which go to zero in the limit. The comic suggests that because these quantities are very small, they are unimportant, when in reality the study of quantities that go to zero gives rise to limits and calculus.<br />
<br />
- lower-case upsilon and lower-case nu<br />
<br />
- lower-case mu<br />
<br />
The SI prefix for "micro" = 10<sup>-6</sup>, representing very small quantities: a micrometer (μm) is tens of times smaller than the width of a human hair, a microgram (μg) is one single fine speck of flour, both of which are barely visible with the bare human eye nor feelable through the skin.<br />
<br />
- capital sigma<br />
<br />
Typically used as a symbol for summation of a series of numbers.<br />
<br />
- capital pi<br />
<br />
Typically used as a symbol for multiplication of a series of numbers.<br />
<br />
- lower-case zeta<br />
<br />
- lower-case beta<br />
<br />
This could be a reference to the typical usage of beta to represent coefficients of independent variables in the [http://https://en.wikipedia.org/wiki/Ordinary_least_squares#Linear_model ordinary least squares regression model]. Regression can potentially have a large number of independent variables, hence potentially many different betas (differentiated by subscript, or compacted into matrix notation) would be used.<br />
<br />
- lower-case alpha<br />
<br />
- capital omega<br />
<br />
- lower-case omega<br />
<br />
- lower-case sigma<br />
<br />
In statistics, commonly refers to the standard deviation of a distribution. Statistics often attempts to use simplified models to explain real-world phenomena.<br />
<br />
- lower-case ksi<br />
<br />
- lower-case gamma<br />
<br />
Gamma ray is the most powerful classification of electromagnetic radiation AKA "light", and powerful lights are frequently associated with high-tech, futuristic devices and weapons, hence "space noises".<br />
<br />
Alternatively, this might be a reference to the Lorentz factor, an important variable in special relativity calculations.<br />
<br />
- lower-care rho<br />
<br />
- capital ksi<br />
<br />
- lower-case psi<br />
<br />
A pun: psi resembles a trident, associated with ocean god Poseidon in Greek mythology (Triton is his son), but psi is also used in math for wave ''functions''.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
<br />
:What Greek letters mean in equations<br />
<br />
:π This math is either very simple or impossible.<br />
:Δ Something has changed.<br />
:δ Something has changed and it's a mathematician's fault.<br />
:θ Circles!<br />
:Φ '''''O R B S'''''<br />
:ϵ Not important, don't worry about it.<br />
:υ,ν Is that a V or a U? Or...oh no, it's one of ''those''.<br />
:μ This math is cool but it's not about anything that you will ever see or touch, so whatever.<br />
:Σ Thank you for purchasing ''Addition Pro''®!<br />
:Π ...and the ''Multiplication''® expansion pack!<br />
:ζ This math will only lead to more math.<br />
:β There are just too many coefficients.<br />
:α Oh boy, now '''''this''''' is math about something real. This is math that could '''''kill''''' someone.<br />
:Ω Oooh, ''some'' mathematician thinks their function is cool and important.<br />
:ω A lot of work went into these equations and you are going to die here among them.<br />
:σ Some poor soul is trying to apply this math to real life and it's not working.<br />
:ξ Either this is terrifying mathematics or there was a hair on the scanned page.<br />
:γ ''Zoom'' pew pew pew [space noises] ''zoooom!''<br />
:ρ Unfortunately, the test vehicle suffered an unexpected wing separation event.<br />
:Ξ Greetings! We hope to learn a great deal by exchanging knowledge with your Earth mathematicians.<br />
:ψ You have entered the domain of King Trition, ruler of the waves.<br />
<br />
{{comic discussion}}</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2014:_JWST_Delays&diff=2231062014: JWST Delays2021-12-26T04:32:48Z<p>Captain Video: /* Explanation */</p>
<hr />
<div><noinclude>:''"2014", this comic's number, redirects here. For the comic named "2014", see [[1311: 2014]].''</noinclude><br />
{{comic<br />
| number = 2014<br />
| date = July 2, 2018<br />
| title = JWST Delays<br />
| image = jwst_delays.png<br />
| titletext = Since delays should get less likely closer to the launch, most astronomers in 2018 believed the expansion of the schedule was slowing, but by early 2020 new measurements indicated that it was actually accelerating.<br />
}}<br />
<br />
==Explanation==<br />
<br />
The {{w|James Webb Space Telescope}} (JWST) is a {{w|space telescope}} created to be the successor of the {{w|Hubble Space Telescope}}. <br />
<br />
The telescope has been in development since 1996, but has been plagued by numerous delays and cost overruns. This comic was likely inspired by the most recent [https://nasa.gov/press-release/nasa-completes-webb-telescope-review-commits-to-launch-in-early-2021 delay announcement], which was posted on June 27, 2018. At that time, the JWST was scheduled to launch on March 30, 2021.<br />
<br />
* In July 2020, this was pushed back further to October 31, 2021 due to the coronavirus pandemic.<br />
* In June 2021, it was announced that the launch day is likely slip to at least mid-November 2021.<br />
* On September 8, 2021, ESA announced that the official planned launch date is [https://www.esa.int/Science_Exploration/Space_Science/Webb/Targeted_launch_date_for_Webb_18_December_2021 December 18, 2021.]<br />
* On November 22, 2021, NASA announced that the official planned launch date was delayed by four days to December 22, 2021, following a problem encountered when mating JWST to its payload adapter.<br />
* On December 15, 2021, NASA announced that the official planned launch date was delayed by two days to December 24, 2021, following a [https://www.space.com/james-webb-space-telescope-launch-delay-december-24 communications issue between JWST and the launch vehicle]<br />
* On December 21, 2021, NASA announced that the official planned launch date was delayed by one day to December 25, 2021 due to [https://www.nasa.gov/feature/james-webb-space-telescope-launch-update adverse weather at the launch site]<br />
* On December 25, 2021, the telescope was successfully launched.<br />
<br />
This comic portrays the launch delays and the new predicted launch years and the times at which those predictions were made. There have been so many delays in this project that you can plot a line of best fit with a surprisingly high degree of accuracy. Randall says optimistically that the line’s slope is less than one (there is less than one year of ''new'' delay per year of elapsed time), implying, of course, that if events continue without further intervention, it will eventually be built, with a predicted date of late 2026.<br />
<br />
The title text alludes to the famous research over the {{w|Accelerating expansion of the universe|universe’s accelerating expansion}}. The expansion had been predicted to be slowing due to gravity from everything in the universe; instead, it was found to be accelerating since about 5 billion years ago. Here, Randall looks at the apparently ever-delaying schedule and observes that the delay per time does not decrease, although the date gets nearer (which should help to schedule the launch date, as research and unknown parameters are replaced with engineering and exact predictions and measurements). However, this delay inflation contradicts Randall's usage of a linear trendline. Given the {{w|COVID-19 pandemic}} brought some additional delays in 2020 and 2021, the "early 2020" date was perhaps unintentionally prescient.<br />
<br />
The Wikipedia article linked above includes a {{w|James Webb Space Telescope#Cost and schedule issues|table}} which provides the data points for the chart:<br />
<br />
{| class=wikitable<br />
! width=35 | Year !! Planned<br />launch !! Time left<br />(years)<br />
|-<br />
| 1997 || 2007 || 10<br />
|-<br />
| 1998 || 2007 || 9<br />
|-<br />
| 1999 || 2007 to 2008 || 8-9<br />
|-<br />
| 2000 || 2009 || 9<br />
|-<br />
| 2002 || 2010 || 8<br />
|-<br />
| 2003 || 2011 || 8<br />
|-<br />
| 2005 || 2013 || 8<br />
|-<br />
| 2006 || 2014 || 8<br />
|-<br />
| 2008 || 2014 || 6<br />
|-<br />
| 2010 || 2015 to 2016 || 5-6<br />
|-<br />
| 2011 || 2018 || 7<br />
|-<br />
| 2013 || 2018 || 5<br />
|-<br />
| 2017 || 2019 || 2<br />
|-<br />
|2018 || 2020 || 2<br />
|-<br />
|2018 || 2021 || 3<br />
|-<br />
|2020 || 2021 || 1<br />
|-<br />
|2021 || 2021 || 0<br />
|}<br />
<br />
==Transcript==<br />
:[Top caption, in the panel:]<br />
:James Webb Space Telescope<br />
:[Subtitle of top caption:]<br />
:Launch Delays<br />
<br />
:[There is a positive-quadrant only line graph. The x- axis is labeled 'Current Date' and the y axis is labeled 'Planned Launch Date'. The dates on both of the axes range from 1995 to 2030.]<br />
:[In the graph are 15 points, starting at (1997,2007) and extending at a slope of a little less than one. The most recent one is labeled 'Now: 2021'.]<br />
:[There are two lines on the graph: a red one and a dashed black one. The red one is a regression of the points on the graph. It has a slope of about ⅔. The black one is a line with a slope of one. They intersect at the point (2026,2026), marked by the label 'Late 2026'?]<br />
<br />
:[Caption below the panel:]<br />
:Look, at least the slope is less than one.<br />
<br />
{{comic discussion}}<br />
<br />
[[Category:Comics with color]]<br />
[[Category:Astronomy]]<br />
[[Category:Space probes]]<br />
[[Category:Line graphs]]<br />
[[Category:Extrapolation]]</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2553:_Incident_Report&diff=2224292553: Incident Report2021-12-10T23:31:27Z<p>Captain Video: /* Explanation */</p>
<hr />
<div>{{comic<br />
| number = 2553<br />
| date = December 10, 2021<br />
| title = Incident Report<br />
| image = incident_report.png<br />
| titletext = Increasing-precision timestamps are the Jaws theme of incident reports.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by an OVERLY-PRECISE TEMPORAL SHARK - Title-text still pending, and particularly bare-bones explanation for first draft. Do NOT delete this tag too soon.}}<br />
<br />
An {{w|incident report}} describes the events that happen before something goes wrong; this usually involves describing what time related events happen at. In this comic, a report at a {{w|nuclear power plant}} on the day of the comic's publishing starts with particularly vague timestamps (that a package of fireworks arrived "roughly 18 hours prior" to it), then uses false minute-level precision ("14:00" and "14:20", which could reasonably be five minutes off in either direction), then actual minute-level precision ("14:28"), then second-level precision ("14:29:22" and "14:29:26").<br />
<br />
This suggests that the ''clock'' time is really a proxy for the ''amount'' of time before one specific moment where everything falls apart, and when seconds start appearing, it implies that the recollection is within a few minutes of the disaster. Normally the increased level of precision reflects close monitoring capabilities of the affected system and/or detailed analysis by incident investigators.<br />
<br />
In many situations, incident reports are anonymized as shown to protect the identities of those people involved in the incidents. Hence the term "technician A" rather than revealing publicly that [[Megan]] was the one who juggled the clubs which knocked the birthday candles into the fireworks leading to the consequent horror of 10 December 2021 - a day that will live in infamy forever more.<br />
<br />
Examples of real-life incident reports with second-level precision timestamps showing the increasing precision around critical moments include:<br />
* [https://spaceflightnow.com/challenger/timeline/ Explosion] of the Space Shuttle Challenger <br />
* [https://world-nuclear.org/information-library/safety-and-security/safety-of-plants/appendices/chernobyl-accident-appendix-1-sequence-of-events.aspx Chernobyl explosion]<br />
<br />
Although the comic refers to {{w|Juggling club|juggling "pins"}}, jugglers commonly refer call those props as "clubs." It is possible Randall is confusing the {{w|Bowling pin|similarly shaped objects}} in 10-pin bowling to juggling clubs. "Pins" are another name for {{W|nuclear fuel rod}}s, which control the speed of a nuclear reaction within a nuclear power plant. No sane reactor staff would juggle{{citation needed}} these complex, heavy and expensive pieces of equipment.<br />
<br />
The title text refers to the [https://www.youtube.com/watch?v=ZvCI-gNK_y4 theme music] from the 1975 film ''{{w|Jaws (film)|Jaws}}'', which has come to represent impending danger.<br />
<br />
9603120071 is an actual accession number for an [https://adamswebsearch2.nrc.gov/webSearch2/main.jsp?AccessionNumber=9603120071 incident] at San Onofre Nuclear Generating Station in 1996. Four slightly contaminated stray kittens were found, cleaned, and adopted. No clock times were mentioned in the report.<br />
<br />
Real-world nuclear power stations have strictly regulated control rooms which would prevent the simultaneous presence of fireworks, juggling and birthday celebrations.{{Citation needed}}. There is no East Valley nuclear power plant, but there are two nuclear power plants in Beaver Valley, Pennsylvania.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
:Facility: East Valley Nuclear Plant<br />
:Date: 12/10/2021<br />
:Report ID: 9603120071<br />
:Event description: Roughly '''18 hours''' prior to the incident, an Amazon package containing fireworks was mistakenly delivered to the reactor control room and left under the console. <br />
:The next day, at approximately '''14:00''', technician A arrived at the facility with a bag containing four juggling pins. At '''14:20''', technician A entered the control room, and joined technician B at the console. <br />
:At '''14:28''', technician C exited the elevator and approached the control room holding a birthday cake intended for technician B.<br />
:At '''14:29:22''', technician A said "Hey [technician B], check out this cool trick I learned" while taking out the juggling pins. Technician B turned to look just as, at '''14:29:26''', technician C entered holding the cake.<br />
<br />
:[Caption below the panel]:<br />
:You know things are about to get bad when the incident report starts including seconds in the timestamps.<br />
<br />
:[Title Text]:<br />
:Increasing-precision timestamps are the Jaws theme of incident reports.<br />
{{comic discussion}}</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=Talk:2549:_Edge_Cake&diff=221713Talk:2549: Edge Cake2021-12-02T06:11:12Z<p>Captain Video: </p>
<hr />
<div><!--Please sign your posts with ~~~~ and don't delete this text. New comments should be added at the bottom.--><br />
<br />
The cake being all edges is a reference to everything about her birth being an edge case.<br />
[[Special:Contributions/172.70.110.227|172.70.110.227]] 03:41, 2 December 2021 (UTC)<br />
: It seems likely that the title of the comic is a related pun: her birthday is an edge case, and so she has an edge cake.[[Special:Contributions/162.158.106.221|162.158.106.221]] 04:22, 2 December 2021 (UTC)<br />
So is Hairbun officially named Emily now, sort of like how all instances of Megan are Megan even though she's only called that once? I know all the names here are just placeholders of convenience, but even then I've never know what the rules for naming are. [[User:Captain Video|Captain Video]] ([[User talk:Captain Video|talk]]) 06:11, 2 December 2021 (UTC)</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2548:_Awful_People&diff=2215762548: Awful People2021-11-30T00:24:18Z<p>Captain Video: </p>
<hr />
<div>{{comic<br />
| number = 2548<br />
| date = November 29, 2021<br />
| title = Awful People<br />
| image = awful_people.png<br />
| titletext = Hm, this burger place has a couple of good reviews, but LakeSlayer7 says he got food poisoning there and everyone should try this other place down by the lake instead.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a NORMAL PEER (Maybe) - Please change this comment when editing this page. Do NOT try that other place down by the lake.}}<br />
<br />
Megan and Cueball are having a conversation about social media. Megan relates a negative comment she got from a stranger about her taste in movies. The twist is that it turns out the person criticizing her was a murderer. Although this does not inherently negate his taste in movies{{citation needed}}, it does free Megan from the burden of weighing his opinions equally to her own.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
{{comic discussion}}<br />
<br />
[[Category:Comics featuring Blondie]]<br />
[[Category:Comics featuring Cueball]]<br />
[[Category:Comics featuring Megan]]</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2541:_Occam&diff=2207532541: Occam2021-11-12T21:56:12Z<p>Captain Video: Simplifying a little</p>
<hr />
<div>{{comic<br />
| number = 2541<br />
| date = November 12, 2021<br />
| title = Occam<br />
| image = occam.png<br />
| titletext = Oh no, Murphy just picked up the razor.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a BOT THAT ONLY CREATES ALL PAGES NOT MENTIONING ITSELF - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
This comic conflates three conceptual approaches. {{w|Occam's Razor}}, the {{w|Barber paradox}} and {{w|Murphy's Law}}.<br />
<br />
Occam's Razor suggests that explanations should not postulate more entities than necessary. It is often phrased as "the simplest explanation is usually correct". In philosophy a '{{w|Philosophical razor|razor}}' is a principle that conceptually cuts away alternative explanations.<br />
<br />
The Barber Paradox is derived from {{w|Russell's paradox}}. A barber is known to shave (presumably with a physical razor) all men in his town who do not shave themselves, and none of the men who shave themselves. The paradox is whether the barber does or does not shave himself. One solution is for the barber not to be a man.<br />
<br />
Megan invokes Occam's Razor with the words "the simplest explanation" as well as Occam's name, and goes on to propose a solution to who shaves the barber. (Her proposal does not resolve the paradox, as someone other than the barber would shave someone who doesn't shave himself.)<br />
<br />
The titletext invokes Murphy's Law: the expectation that if anything can go wrong it will. Shaving with a {{w|Straight razor|cut-throat razor}} has failure modes including one explained by this name.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
[One panel. Megan and Cueball walking.]<br />
<br />
Megan: The simplest explanation is that Occam shaves the barber.<br />
<br />
{{comic discussion}}</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2539:_Flinch&diff=2206062539: Flinch2021-11-10T01:19:10Z<p>Captain Video: /* Explanation */</p>
<hr />
<div>{{comic<br />
| number = 2539<br />
| date = November 8, 2021<br />
| title = Flinch<br />
| image = flinch.png<br />
| titletext = Premed: "Does this count for a physics credit? Can we shorten the string so I can get it done faster? And can we do one where it hits me in the face? I gotta do a thing for first aid training right after."<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a WOUNDED POSTMED STUDENT - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
[[Cueball]] is performing [https://youtu.be/4a0FbQdH3dY?t=1518 a common physics demonstration] in which a heavy ball is hung from a rope or cable. The demonstrator, or a volunteer, pulls the ball back until it's close to their face (possibly even touching it), then releases it, allowing it to swing, and then return. Due to conservation of energy, the ball cannot return any further than it's original release point, making it impossible for the person to be struck by it. Because a heavy pendulum will tend to lose little energy on each swing, it will come back very close to its original point, so the experiment creates a conflict between the instinctive desire to escape a heavy object flying at your face, and the theoretical knowledge that it won't harm you. <br />
<br />
[[Megan]] is a physicist, who understands the principles of the experiment and claims she won't flinch, confident that it can't harm her.<br />
<br />
[[Hairy]] is a biologist, and implies that he has no intention of avoiding the flinch reflex, as he trusts the {{w|Reflex|automatic reflexes}} that the human body has evolved more than he trusts the premise of the experiment. In both [[755: Interdisciplinary]] and [[1670: Laws of Physics]], the same experiment is referenced. In the title text of the latter [[Randall]] makes a very similar argument as the biologist does here. <br />
<br />
[[Ponytail]], an engineer, replies that she doesn't trust Cueball to have hung the pendulum correctly. Engineers are trained in science, but work with practical applications, and tend to be very aware that practice is rarely as simple as scientific theories might imply. Even if the physical laws are constant, the experiment might not go according to plan. For example, if the cable were to snap or come loose while swinging toward the subject, the ball could strike them in the body, or land on their feet. If the cable is more elastic than anticipated, it could stretch unpredictably, once again striking someone. If the anchor point is not stable, it could shift during the experiment, once again causing harm. Also if the ball is not released but pushed, or if the one releasing it leans forward after release they might get hit in the face.<br />
<br />
The punch line basically makes the point that failure to trust the safety of an experiment doesn't necessarily imply a lack of scientific knowledge. If you lack confidence in the design of an experiment, then it's not safe to assume that the laws of physics will protect you. <br />
<br />
The title text shows a pre-med student's response. {{w|Pre-medical}} university courses have a reputation for being more intense and demanding than other undergraduate degrees, so the student is portrayed as being very stressed and time-conscious; showing little interest in the experiment itself, only in how it impacts their degree. <br />
<br />
The student first asks if participating in the demonstration will count for a physics credit, implying that they're not willing to spend time on it unless it contributes to their academic requirements. They then ask if they can shorten the string to make the demonstration go faster. Shortening a pendulum does, indeed, cause it to swing faster, but caring about the few seconds this would save is an exaggerated sense of time management. Finally, they ask to do a variant where they ''deliberately'' get struck in the face, because they have a "thing for first aid training" immediately after. This would likely injure them, but the student is apparently willing to sacrifice their own safety and well-being in service to their academic career. It's not clear how this would help, although it could potentially help ''others'' learn first aid by having them practice on the new injury.<br />
<br />
==Transcript==<br />
:[Cueball holds a bowling ball in both hands. It is attached to a string that goes behind him and up disappearing off panel around double his height. He is talking to Megan, Hairy, and Ponytail who is looking at him. Between Cueball and the other three is a cross in a dotted circle on the floor.]<br />
:Cueball: If you stand with the bowling ball in front of your face and let go, will you flinch when it swings back?<br />
<br />
:[Zoom in on Megan in a slim panel. There is a caption in a frame above her.]<br />
:Caption: Physicist<br />
:Megan: I won't flinch.<br />
:Megan: I trust conservation of energy.<br />
<br />
:[Zoom in on Hairy, in a wide panel. He has lifted arm holding his hand palm up toward Cueball (who is off-panel). There is a caption in a frame above him.]<br />
:Caption: Biologist<br />
:Hairy: I trust my flinch reflex, which was honed by millions of years of evolution to protect my delicate face. I'm not messing with it.<br />
<br />
:[Zoom in on Ponytail in a slim panel. There is a caption in a frame above her.]<br />
:Caption: Engineer<br />
:Ponytail: I don't trust that you hung that thing up correctly.<br />
<br />
{{comic discussion}}<br />
<br />
[[Category:Comics featuring Cueball]]<br />
[[Category:Comics featuring Megan]]<br />
[[Category:Comics featuring Hairy]]<br />
[[Category:Comics featuring Ponytail]]<br />
[[Category:Physics]]<br />
[[Category:Biology]]</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2539:_Flinch&diff=2205262539: Flinch2021-11-09T02:13:21Z<p>Captain Video: </p>
<hr />
<div>{{comic<br />
| number = 2539<br />
| date = November 8, 2021<br />
| title = Flinch<br />
| image = flinch.png<br />
| titletext = Premed: "Does this count for a physics credit? Can we shorten the string so I can get it done faster? And can we do one where it hits me in the face? I gotta do a thing for first aid training right after."<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a WOUNDED PREMED STUDENT - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
Cueball is demonstrating a bowling ball pendulum to a group of bystanders with different science backgrounds. He asks if they'll flinch after the ball is released and swings toward them on its return arc.<br />
<br />
The first bystander, a physicist (Megan) understands the principles of the experiment and claims she won't flinch. She knows that, as long as it's just ''released'' (as opposed to being pushed), the ball won't return further than its point of release.<br />
<br />
The second bystander, a biologist (Hairy) seems to indicate that he expects to flinch, but he feels this is natural and doesn't intend to fight it. It is natural, and in fact the body comes with many kinds of {{w|Reflex|automatic reflexes}}.<br />
<br />
The third bystander, an engineer (Ponytail) ignores Cueball's question and declares his apparatus suspect. An experiment that overlaps with the bowling ball pendulum, the {{w|Foucault pendulum}}, is used to demonstrate the Earth's rotation. This effect is best demonstrated over a long timeframe, which in turn requires a long chain that can support bigger swings, allowing more energy to be put into the system at the start of the experiment. This, in turn, means the easiest solution is to hang the ball and chain from the ceiling, which can be dangerous for those without training - and their bystanders.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
{{comic discussion}}<br />
<br />
[[Category:Comics featuring Cueball]]<br />
[[Category:Comics featuring Hairy]]<br />
[[Category:Comics featuring Megan]]<br />
[[Category:Comics featuring Ponytail]]</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2539:_Flinch&diff=2205252539: Flinch2021-11-09T02:12:52Z<p>Captain Video: Categories</p>
<hr />
<div>{{comic<br />
| number = 2539<br />
| date = November 8, 2021<br />
| title = Flinch<br />
| image = flinch.png<br />
| titletext = Premed: "Does this count for a physics credit? Can we shorten the string so I can get it done faster? And can we do one where it hits me in the face? I gotta do a thing for first aid training right after."<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a WOUNDED PREMED STUDENT - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
Cueball is demonstrating a bowling ball pendulum to a group of bystanders with different science backgrounds. He asks if they'll flinch after the ball is released and swings toward them on its return arc.<br />
<br />
The first bystander, a physicist (Megan) understands the principles of the experiment and claims she won't flinch. She knows that, as long as it's just ''released'' (as opposed to being pushed), the ball won't return further than its point of release.<br />
<br />
The second bystander, a biologist (Hairy) seems to indicate that he expects to flinch, but he feels this is natural and doesn't intend to fight it. It is natural, and in fact the body comes with many kinds of {{w|Reflex|automatic reflexes}}.<br />
<br />
The third bystander, an engineer (Ponytail) ignores Cueball's question and declares his apparatus suspect. An experiment that overlaps with the bowling ball pendulum, the {{w|Foucault pendulum}}, is used to demonstrate the Earth's rotation. This effect is best demonstrated over a long timeframe, which in turn requires a long chain that can support bigger swings, allowing more energy to be put into the system at the start of the experiment. This, in turn, means the easiest solution is to hang the ball and chain from the ceiling, which can be dangerous for those without training - and their bystanders.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
{{comic discussion}}<br />
<br />
[[Category:Comics featuring Cueball]]<br />
[[Category:Comics featuring Hairy]]<br />
[[Category:Comics featuring Megan]]</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2539:_Flinch&diff=2205242539: Flinch2021-11-09T02:10:34Z<p>Captain Video: /* Explanation */</p>
<hr />
<div>{{comic<br />
| number = 2539<br />
| date = November 8, 2021<br />
| title = Flinch<br />
| image = flinch.png<br />
| titletext = Premed: "Does this count for a physics credit? Can we shorten the string so I can get it done faster? And can we do one where it hits me in the face? I gotta do a thing for first aid training right after."<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a WOUNDED PREMED STUDENT - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
Cueball is demonstrating a bowling ball pendulum to a group of bystanders with different science backgrounds. He asks if they'll flinch after the ball is released and swings toward them on its return arc.<br />
<br />
The first bystander, a physicist (Megan) understands the principles of the experiment and claims she won't flinch. She knows that, as long as it's just ''released'' (as opposed to being pushed), the ball won't return further than its point of release.<br />
<br />
The second bystander, a biologist (Hairy) seems to indicate that he expects to flinch, but he feels this is natural and doesn't intend to fight it. It is natural, and in fact the body comes with many kinds of {{w|Reflex|automatic reflexes}}.<br />
<br />
The third bystander, an engineer (Ponytail) ignores Cueball's question and declares his apparatus suspect. An experiment that overlaps with the bowling ball pendulum, the {{w|Foucault pendulum}}, is used to demonstrate the Earth's rotation. This effect is best demonstrated over a long timeframe, which in turn requires a long chain that can support bigger swings, allowing more energy to be put into the system at the start of the experiment. This, in turn, means the easiest solution is to hang the ball and chain from the ceiling, which can be dangerous for those without training - and their bystanders.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
{{comic discussion}}</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2539:_Flinch&diff=2205212539: Flinch2021-11-09T02:08:28Z<p>Captain Video: /* Explanation */</p>
<hr />
<div>{{comic<br />
| number = 2539<br />
| date = November 8, 2021<br />
| title = Flinch<br />
| image = flinch.png<br />
| titletext = Premed: "Does this count for a physics credit? Can we shorten the string so I can get it done faster? And can we do one where it hits me in the face? I gotta do a thing for first aid training right after."<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a WOUNDED PREMED STUDENT - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
Cueball is demonstrating a {{w|Foucault pendulum}} to a group of bystanders with different science backgrounds. He asks if they'll flinch after the ball is released and swings toward them on its return arc.<br />
<br />
The first bystander, a physicist (Megan) understands the principles of the experiment and claims she won't flinch. She knows that, as long as it's just ''released'' (as opposed to being pushed), the ball won't return further than its point of release.<br />
<br />
The second bystander, a biologist (Hairy) seems to indicate that he expects to flinch, but he feels this is natural and doesn't intend to fight it. It is natural, and in fact the body comes with many kinds of {{w|Reflex|automatic reflexes}}.<br />
<br />
The third bystander, an engineer (Ponytail) ignores Cueball's question and declares his apparatus suspect. Foucault pendulums are often constructed to demonstrate the Earth's rotation. This effect is best demonstrated over a long timeframe, which in turn requires a long chain that can support bigger swings, allowing more energy to be put into the system at the start of the experiment. This, in turn, means the easiest solution is to hang the ball and chain from the ceiling, which can be dangerous for those without training - and their bystanders.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
{{comic discussion}}</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2539:_Flinch&diff=2205202539: Flinch2021-11-09T02:05:05Z<p>Captain Video: /* Explanation */</p>
<hr />
<div>{{comic<br />
| number = 2539<br />
| date = November 8, 2021<br />
| title = Flinch<br />
| image = flinch.png<br />
| titletext = Premed: "Does this count for a physics credit? Can we shorten the string so I can get it done faster? And can we do one where it hits me in the face? I gotta do a thing for first aid training right after."<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a WOUNDED PREMED STUDENT - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
Cueball is demonstrating a {{w|Foucault pendulum}} to a group of bystanders with different science backgrounds. He asks if they'll flinch after the ball is released and swings toward them on its return arc.<br />
<br />
The first bystander, a physicist (Megan) understands the principles of the experiment and claims she won't flinch. She knows that, as long as it's just ''released'' (as opposed to being pushed), the ball won't return further than its point of release.<br />
<br />
The second bystander, a biologist (Hairy) seems to indicate that he expects to flinch, but he feels this is natural and doesn't intend to fight it. It is natural, and in fact the body comes with many kinds of {{w|Reflex|automatic reflexes}}.<br />
<br />
The third bystandard, an engineer (Ponytail) ignores Cueball's question and declares his apparatus suspect.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
{{comic discussion}}</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2539:_Flinch&diff=2205192539: Flinch2021-11-09T02:02:37Z<p>Captain Video: </p>
<hr />
<div>{{comic<br />
| number = 2539<br />
| date = November 8, 2021<br />
| title = Flinch<br />
| image = flinch.png<br />
| titletext = Premed: "Does this count for a physics credit? Can we shorten the string so I can get it done faster? And can we do one where it hits me in the face? I gotta do a thing for first aid training right after."<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a WOUNDED PREMED STUDENT - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
Cueball is demonstrating a {{w|Foucault pendulum}} to a group of bystanders with different science backgrounds. He asks if they'll flinch after the ball is released and swings toward them on its return arc<br />
<br />
The first bystander, a physicist (Megan) understands the principles of the experiment and claims she won't flinch. She knows that, as long as it's just ''released'' (as opposed to being pushed), the ball won't return further than its point of release.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
{{comic discussion}}</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2537:_Painbow_Award&diff=2202972537: Painbow Award2021-11-03T23:30:31Z<p>Captain Video: </p>
<hr />
<div>{{comic<br />
| number = 2537<br />
| date = November 3, 2021<br />
| title = Painbow Award<br />
| image = painbow_award.png<br />
| titletext = This year, our team took home the dark blue ribbon, better than the midnight blue we got last year but still short of the winning navy blue.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by MELLLVAR - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
This comic makes fun of the sometimes-displeasing color gradients used in the figures for scientific papers by suggesting that the scientists picking them are in competition to use the least-pleasing gradient. The title of the comic is a portmanteau of "pain" and "rainbow" suggesting a humorous name for terrible gradients.<br />
<br />
The gradient here showcases a collection of unintuitive and unhelpful decisions. White fades down into green, which then fades into red (passing through brown in the middle instead of yellow, indicating {{w|subtractive color}} mixing instead of {{w|additive color}} mixing, for no obvious reason). The red then turns ''back'' into green as the intensity increases further. Red and green in close proximity make the power levels hard or impossible to distinguish for those with {{w|Color_blindness#Protanopia|protanopic colorblindness}}. This confusion is repeated at lower power levels, where blue transitions to black and then back again, before finally transitioning back into white. The highest and lowest recorded power levels have the same color value, which is less than ideal.<br />
<br />
Although it's possible (for someone with full color vision) to interpret data from this graph from context clues - the white that fades to green is high-energy white, while the white that fades to blue is low-energy white - there's no benefit to doing things this way, and a lot of downsides.<br />
<br />
Real-world analogues to the Painbow Award include radar meteorology charts, where different types of precipitation have different color schemes that can overlap and blend in confusing transition zones.<br />
<br />
The title text underscores the arbitrary nature of color gradients: It's not intrinsically obvious why navy blue is better than dark blue, or why dark blue is better than midnight blue.<br />
<br />
==Trivia==<br />
* When originally uploaded, the caption used the phrase "color gradient" rather than "color scale"<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
:[A graph named 'Figure 2' with two axes is shown. The vertical axis is labeled 'λ' and the horizontal axis is labeled 'θ (phase)'. On the right side, a bar labeled 'Peak Energy' is shown, with colors starting from black, to green, to red, to green, to yellow, and to white from bottom to top. The center of the graph is a messy shape with ugly gradients from these colors.]<br />
:Caption under the panel: Every year, disgruntled scientists compete for the Painbow Award for worst color scale.<br />
<br />
{{comic discussion}}<br />
<br />
[[Category:Comics with color]]</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2537:_Painbow_Award&diff=2202962537: Painbow Award2021-11-03T23:28:14Z<p>Captain Video: </p>
<hr />
<div>{{comic<br />
| number = 2537<br />
| date = November 3, 2021<br />
| title = Painbow Award<br />
| image = painbow_award.png<br />
| titletext = This year, our team took home the dark blue ribbon, better than the midnight blue we got last year but still short of the winning navy blue.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by MELLLVAR - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
This comic makes fun of the sometimes-displeasing color gradients used in the figures for scientific papers by suggesting that the scientists picking them are in competition to use the least-pleasing gradient.<br />
<br />
The gradient here showcases a collection of unintuitive and unhelpful decisions. White fades down into green, which then fades into red (passing through brown in the middle instead of yellow, indicating {{w|subtractive color}} mixing instead of {{w|additive color}} mixing, for no obvious reason). The red then turns ''back'' into green as the intensity increases further. Red and green in close proximity make the power levels hard or impossible to distinguish for those with {{w|Color_blindness#Protanopia|protanopic colorblindness}}. This confusion is repeated at lower power levels, where blue transitions to black and then back again, before finally transitioning back into white. The highest and lowest recorded power levels have the same color value, which is less than ideal.<br />
<br />
Although it's possible (for someone with full color vision) to interpret data from this graph from context clues - the white that fades to green is high-energy white, while the white that fades to blue is low-energy white - there's no benefit to doing things this way, and a lot of downsides.<br />
<br />
Real-world analogues to the Painbow Award include radar meteorology charts, where different types of precipitation have different color schemes that can overlap and blend in confusing transition zones.<br />
<br />
The title of the comic is a portmanteau of "pain" and "rainbow" suggesting a humorous name for terrible gradients.<br />
<br />
==Trivia==<br />
* When originally uploaded, the caption used the phrase "color gradient" rather than "color scale"<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
:[A graph named 'Figure 2' with two axes is shown. The vertical axis is labeled 'λ' and the horizontal axis is labeled 'θ (phase)'. On the right side, a bar labeled 'Peak Energy' is shown, with colors starting from black, to green, to red, to green, to yellow, and to white from bottom to top. The center of the graph is a messy shape with ugly gradients from these colors.]<br />
:Caption under the panel: Every year, disgruntled scientists compete for the Painbow Award for worst color scale.<br />
<br />
{{comic discussion}}<br />
<br />
[[Category:Comics with color]]</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2537:_Painbow_Award&diff=2202932537: Painbow Award2021-11-03T23:21:50Z<p>Captain Video: </p>
<hr />
<div>{{comic<br />
| number = 2537<br />
| date = November 3, 2021<br />
| title = Painbow Award<br />
| image = painbow_award.png<br />
| titletext = This year, our team took home the dark blue ribbon, better than the midnight blue we got last year but still short of the winning navy blue.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by MELLLVAR - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
This comic makes fun of the sometimes-displeasing color gradients used in the figures for scientific papers by suggesting that the scientists picking them are in competition to use the least-pleasing gradient.<br />
<br />
The gradient here showcases a collection of unintuitive and unhelpful decisions. White fades down into green, which then fades into red (passing through brown in the middle instead of yellow, indicating subtractive color mixing instead of additive color mixing, for no obvious reason). The red then turns ''back'' into green as the intensity increases further. Red and green in close proximity make the power levels hard or impossible to distinguish for those with {{w|Color_blindness#Protanopia|protanopic colorblindness}}.<br />
<br />
This confusion is repeated at lower power levels, where blue transitions to black and then back again, before finally transitioning back into white. The highest and lowest recorded power levels have the same color value, which is less than ideal.<br />
<br />
The title of the comic is a portmanteau of "pain" and "rainbow" suggesting a humorous name for terrible gradients.<br />
<br />
==Trivia==<br />
* When originally uploaded, the caption used the phrase "color gradient" rather than "color scale"<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
:[A graph named 'Figure 2' with two axes is shown. The vertical axis is labeled 'λ' and the horizontal axis is labeled 'θ (phase)'. On the right side, a bar labeled 'Peak Energy' is shown, with colors starting from black, to green, to red, to green, to yellow, and to white from bottom to top. The center of the graph is a messy shape with ugly gradients from these colors.]<br />
:Caption under the panel: Every year, disgruntled scientists compete for the Painbow Award for worst color scale.<br />
<br />
{{comic discussion}}<br />
<br />
[[Category:Comics with color]]</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2537:_Painbow_Award&diff=2202912537: Painbow Award2021-11-03T23:19:05Z<p>Captain Video: /* Explanation */</p>
<hr />
<div>{{comic<br />
| number = 2537<br />
| date = November 3, 2021<br />
| title = Painbow Award<br />
| image = painbow_award.png<br />
| titletext = This year, our team took home the dark blue ribbon, better than the midnight blue we got last year but still short of the winning navy blue.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by MELLLVAR - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
This comic makes fun of the sometimes-displeasing color gradients used in the figures for scientific papers by suggesting that the scientists picking them are in competition to use the least-pleasing gradient.<br />
<br />
The gradient here showcases a collection of unintuitive and unhelpful decisions. White fades up into green, which then fades into red (passing through brown in the middle instead of yellow, indicating subtractive color mixing instead of additive color mixing, for no obvious reason. The red then turns ''back'' into green as the intensity increases further. Red and green in close proximity make the power levels hard or impossible to distinguish for those with {{w|Color_blindness#Protanopia|protanopic colorblindness}}.<br />
<br />
The title of the comic is a portmanteau of "pain" and "rainbow" suggesting a humorous name for terrible gradients.<br />
<br />
==Trivia==<br />
* When originally uploaded, the caption used the phrase "color gradient" rather than "color scale"<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
:[A graph named 'Figure 2' with two axes is shown. The vertical axis is labeled 'λ' and the horizontal axis is labeled 'θ (phase)'. On the right side, a bar labeled 'Peak Energy' is shown, with colors starting from black, to green, to red, to green, to yellow, and to white from bottom to top. The center of the graph is a messy shape with ugly gradients from these colors.]<br />
:Caption under the panel: Every year, disgruntled scientists compete for the Painbow Award for worst color scale.<br />
<br />
{{comic discussion}}<br />
<br />
[[Category:Comics with color]]</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2521:_Toothpaste&diff=2185872521: Toothpaste2021-09-28T04:46:04Z<p>Captain Video: /* Explanation */</p>
<hr />
<div>{{comic<br />
| number = 2521<br />
| date = September 27, 2021<br />
| title = Toothpaste<br />
| image = toothpaste.png<br />
| titletext = "9 out of 10 dentists have banned me from their offices."<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a THE 10th DENTIST - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
Here, we see more of [[Megan]]'s "wordplay". Unlike in [[2352: Synonym Date]] and [[2245: Edible Arrangements]], she's not trying to make her friend uncomfortable -- it just happens anyway.<br />
<br />
Putting toothpaste back in its tube is often used as an analogy for something irreversible, such as how you can't undo speaking. Megan rejects this assertion and says that you actually ''can'' put toothpaste back in its tube. She still believes that the analogy holds, and therefore she ''can'' unsay something - which she attempts to do to her description of returned toothpaste when Cueball is disgusted by it.<br />
<br />
Toothpaste is normally loaded into the tube from the back, before it is crimped shut. However, it should ''technically'' be possible to push an extruded amount of paste back in from the front by wrapping one's lips around the whole front of the tube and blowing, provided the paste still covers the hole. This positive pressure can reinflate the tube the same way one blows up a balloon. However, blowing the toothpaste back into the tube would be highly unsanitary, and as the main purpose of toothpaste is to clean teeth, the end result is both counterproductive and disgusting.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
:Cueball: I can't believe she said that. <br />
:Cueball: She apologized, but you can't put the toothpaste back in the tube.<br />
:Megan: Sure you can; it's easy. You just put your mouth over the opening.<br />
:Cueball: Well, ''that's'' the worst thing you've ever said.<br />
:Megan: Sorry, I can take it back. It's just like-<br />
:Cueball: NO!<br />
<br />
:Title text: 9 out of 10 dentists have banned me from their offices.<br />
<br />
{{comic discussion}}</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2521:_Toothpaste&diff=2185862521: Toothpaste2021-09-28T04:44:17Z<p>Captain Video: </p>
<hr />
<div>{{comic<br />
| number = 2521<br />
| date = September 27, 2021<br />
| title = Toothpaste<br />
| image = toothpaste.png<br />
| titletext = "9 out of 10 dentists have banned me from their offices."<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a THE 10TH DENTIST - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
Here, we see more of [[Megan]]'s "wordplay". Unlike in [[2352: Synonym Date]] and [[2245: Edible Arrangements]], she's not trying to make her friend uncomfortable -- it just happens anyway.<br />
<br />
Putting toothpaste back in its tube is often used as an analogy for something irreversible, such as how you can't undo speaking. Megan rejects this assertion and says that you actually ''can'' put toothpaste back in its tube. She still believes that the analogy holds, and therefore she ''can'' unsay something - which she attempts to do to her description of returned toothpaste when Cueball is disgusted by it.<br />
<br />
Toothpaste is normally loaded into the tube from the back, before it is crimped shut. However, it should ''technically'' be possible to push an extruded amount of paste back in from the front by wrapping one's lips around the whole front of the tube and blowing. This positive pressure can reinflate the tube the same way one blows up a balloon. However, blowing the toothpaste back into the tube would be highly unsanitary, and as the main purpose of toothpaste is to clean teeth, the end result is both counterproductive and disgusting.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
:Cueball: I can't believe she said that. <br />
:Cueball: She apologized, but you can't put the toothpaste back in the tube.<br />
:Megan: Sure you can; it's easy. You just put your mouth over the opening.<br />
:Cueball: Well, ''that's'' the worst thing you've ever said.<br />
:Megan: Sorry, I can take it back. It's just like-<br />
:Cueball: NO!<br />
<br />
:Title text: 9 out of 10 dentists have banned me from their offices.<br />
<br />
{{comic discussion}}</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2516:_Hubble_Tension&diff=2181352516: Hubble Tension2021-09-16T22:11:56Z<p>Captain Video: </p>
<hr />
<div>{{comic<br />
| number = 2516<br />
| date = September 15, 2021<br />
| title = Hubble Tension<br />
| image = hubble_tension.png<br />
| titletext = Oh, wait, I might've had it set to kph instead of mph. But that would make the discrepancy even wider!<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by Dave - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
[[Ponytail]] is telling [[Cueball]] about the {{w|expansion of the universe}} telling him that there are three main estimates of the rate of expansion, and that they all disagree. She then tells him of the two well known (and very complicated) methods, and finally the joke is that the third method is performed by a guy named Dave (who replies from off-panel), and he claims to measure the distances with a radar gun, as if the galaxies were speeding here on Earth.<br />
<br />
The fact that most {{w|galaxies}} are receding from us, and that the distance to the galaxy is directly proportional to the speed (as measured by {{w|red-shift}}) was discovered in the 1920s by {{w|Edwin Hubble}} and others. This constant of proportionality is known as the {{w|Hubble Constant}}.<br />
<br />
One way of measuring the Hubble Constant is to measure the distance to (relatively) nearby galaxies. Once distance is obtained, speed can be easily obtained by measuring the red-shift and thus the Hubble Constant calculated. Measuring the distance turns out to be fiendishly difficult because a distant bright star looks the same as a dim star that is closer, and localized movements can influence the speed of recession &mdash; though less significantly, for multiple reasons, the further away are the objects that you study.<br />
<br />
In practice, astronomers have a number of ways of measuring distance that work at different scales, and they can be built upon to measure distance to far away galaxies. This is known as the {{w|Cosmic distance ladder}}. <br />
<br />
The first rung is {{w|parallax}}. As the Earth orbits around the Sun, nearby stars appear to move slightly relative to distant stars; a star that moves by one second of arc is said to have a distance of 1 {{w|Parsec}} &mdash; about 3¼ light years or 30 trillion (3x10<sup>13</sup>) kilometers. <br />
<br />
The next rung is {{w|Cepheid variables}}, which periodically brighten and dim. The frequency of variation is related to the absolute brightness of the star, and thus by comparing the absolute to the relative brightness (subject to the {{w|Inverse-square law}} where not otherwise obscured) the distance can be measured. <br />
<br />
The final rung is {{w|Type Ia supernova}}, which occur when an accreting {{w|white dwarf}} exceeds 1.4 solar masses. Because the initial mass is always identical, the absolute brightness of the explosion is as well, so the distance can be similarly calculated.<br />
<br />
Putting these together, the best measurement of the Hubble Constant is 73 km/s/Mparsec.<br />
<br />
This is in conflict with the other main way of measuring the Hubble Constant, analyzing makeup of the {{w|Cosmic Microwave Background}} (CMB) radiation, which yields a value of 68 km/s/Mparsec. The difference is statistically significant, and well outside the error bounds of each measurement.<br />
<br />
Since the CMB technique relies on our understanding and assumptions about the early universe, as well as on the cosmological effects of General Relativity on large scales, if this discrepancy proved real it could be the gateway to new discoveries in cosmology and gravity, as well as possibly shed light on the origin of the universe and a '{{w|Theory Of Everything}}'. Cosmologists got quite excited about this. It might also be that there was a previously unaccounted-for error in any of the rungs of the cosmological distance ladder, and that once that is fixed, the two results will be consistent.<br />
<br />
The third method introduced in this comic is a guy named Dave who is trying to use a {{w|radar speed gun}} (as used by the police for detecting speeding cars) to try to measure the movement of astronomical bodies. A radar system works by sending electromagnetic radiation from the gun and then measuring the returned radiation to determine how far away or how fast a moderately distant object is moving. Because of the transmission and return times required (and the inverse-square law), a radar device will only be able to get information about the very closest objects, such as the Moon (a type of {{w|Earth–Moon–Earth communication|Moon bounce}}) and other objects orbiting the Earth (or ''perhaps'' the Sun), where the influence of being in orbit utterly dominates over any possible Hubble-shift. And that still needs powerful radar systems like the former {{w|Arecibo Telescope}} to be able to get any useful information that far away, a hand-held radar gun would not be able to 'lock on' across even those distances.<br />
<br />
Going by back-calculating grossly 'idealized' universe models, as suggested by the other two estimates, a receding velocity of 85 miles per hour ('mph'; about 137 kilometers per hour, 'kph' or 'km/h') should be seen at a distance of roughly 1700-1850 light-years, on the order of the thickness of our galactic disc. Much too far to use a radar gun on, also much too close to exclude any significant galactic stellar motions. Much the same is true if the figure is actually 85 kph (1050-1130 ly), as suggested it might be in the title text. It is also dimensionally wrong, as it is quoted as a straight "distance per time", not "distance per time ''per distance''".<br />
<br />
Aside from being practically incorrect, that value of 85 kph relates to around 53 mph, which might be the normally observed traffic speed on certain roads (especially if someone is conspicuously using a radar gun!) if by 'all directions' you effectively mean 'both directions' of traffic flow that Dave could possibly be measuring. Dave may have been referring to the kind of {{w|Ford Galaxy|Galaxy}} that he ''can'' more easily find out the velocity of.<br />
<br />
The comic is likely making fun of the common internet phenomenon of amateur (wannabe?) scientists seeking to discredit established scientific facts by reporting the results of experiments made using everyday tools. Dave has probably heard of the fact that there is no agreement in the scientific measurements of the Hubble constant and decided to try to settle the controversy using the tools at his disposal, without remotely realizing that the margin of error required in the measurements is well outside the range of what can be used with conventional objects.<br />
<br />
==Transcript==<br />
:[Cueball and Ponytail are walking to the right. Ponytail has her palm raised.]<br />
:Ponytail: There are three main estimates of the universe's expansion rate and they all disagree.<br />
<br />
:[They keeping walking to the right.]<br />
:Ponytail: Measurements of star distances suggest the universe is expanding at 73 km/s/megaparsec.<br />
<br />
:[They are still walking to the right.]<br />
:Ponytail: Measurements of the cosmic microwave background suggest it's expanding at 68 km/s/megaparsec.<br />
<br />
:[They continue walking to the right. Ponytail points towards Dave who replies from off-panel to the right.]<br />
:Ponytail: And Dave, who has a radar gun, says it's expanding at 85 mph in all directions.<br />
:Dave (off-panel): ''Those galaxies are really booking it!''<br />
:Ponytail: Thanks, Dave.<br />
<br />
{{comic discussion}}<br />
<br />
[[Category:Comics featuring Cueball]]<br />
[[Category:Comics featuring Ponytail]]<br />
[[Category:Astronomy]]<br />
[[Category:Physics]]</div>Captain Videohttps://www.explainxkcd.com/wiki/index.php?title=2509:_Useful_Geometry_Formulas&diff=2173272509: Useful Geometry Formulas2021-08-31T02:51:35Z<p>Captain Video: /* Explanation */ Ah, okay</p>
<hr />
<div>{{comic<br />
| number = 2509<br />
| date = August 30, 2021<br />
| title = Useful Geometry Formulas<br />
| image = useful_geometry_formulas.png<br />
| titletext = Geometry textbooks always try to trick you by adding decorative stripes and dotted lines.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by an AREA OF A CIRCLE IN A SPHERE. Do NOT delete this tag too soon.}}<br />
<br />
This comic showcases area formulae for sections of four common three-dimensional geometric shapes. Clockwise from the top left, they are a sphere, a cone, a rectangular prism, and a cylinder. The formulas are for the literal area of each shape in 2d, not what it would look like if it were 3d. The top-left formula is for the area of a circle, which is literally what is drawn and not what appears to be a sphere. The formula for the cone is actually the area of a triangle and half-ellipse. And so on.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
{{comic discussion}}</div>Captain Video