explain xkcd - User contributions [en]

2735: Coordinate Plane Closure

2023-02-08T15:23:47Z

Öbc:

{{comic
| number = 2735
| date = February 8, 2023
| title = Coordinate Plane Closure
| image = coordinate_plane_closure_2x.png
| imagesize = 271x376px
| noexpand = true
| titletext = 3D graphs that don't contact the plane in the closure area may proceed as scheduled, but be alert for possible collisions with 2D graph lines that reach the hole and unexpectedly enter 3D space.
}}

==Explanation==
{{incomplete|Created by a 2D graph that has accidently become 3D (and sentient) - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

This comic is a "Math Notice," which is presumably a warning or reminder for mathematicians or others who interact with the field of mathematics. Specifically, this one advises those who are using the coordinate plane to avoid drawing any graphs in the area with a hole until the damage is patched or fixed.

{{w|Coordinate planes}} are used in math for drawing graphs. The joke here is that a small section has been "closed for maintenance," likening the concept of a coordinate plane to an actual physical platform used by math, which is therefore vulnerable to damage such as is shown in the comic. In reality, the coordinate plane cannot be damaged as it is not a tangible thing.{{citation needed}}

The title text clarifies some of the unwanted effects of drawing a graph into the hole, stating that two-dimensional graph lines might accidentally become three-dimensional and interfere with the graphs made there.
==Transcript==

<big>⚠️ Math Notice ⚠️</big>

The coordinate plane will be closed Thursday between (1.5, 1) and (2, 1.5) to repair a hole.

(A coordinate graph is shown, with a gray hole between (1.5, 1) and (2, 1.5). The hole is highlighted with two dots in the corners of a hollow rectangle with split border lines.)

If your graph uses this area, please postpone drawing until Friday or transform it to different coordinates.

{{comic discussion}}

Talk:2221: Emulation

2022-10-20T21:38:39Z

Öbc:

This reminds me of Miii's "world.execute(me)" song.
[[Special:Contributions/172.68.10.172|172.68.10.172]] 05:06, 29 October 2019 (UTC)

Does everyone else also see adds in the middle of the explanation now? It is extremely annoying. :-( Ahh yes, they do, there is a [[Talk:2220:_Imagine_Going_Back_in_Time#Google_ads|section in the previous comics discussion]]. Take further grievances there --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 10:40, 29 October 2019 (UTC)
:My first time seeing it: Right under your comment, LOL! I closed it, wish I could explain that it's because this is a really inappropriate place for an ad. They used to appear unobtrusively on the side, as they should be. [[User:NiceGuy1|NiceGuy1]] ([[User talk:NiceGuy1|talk]]) 04:56, 1 November 2019 (UTC)

I don't see any adds anywhere. ( I also don't see any ads in the middle ;^) [[Special:Contributions/162.158.78.160|162.158.78.160]] 11:34, 29 October 2019 (UTC)

:There's an ad (for me, on this device, just before I came in to edit ''((now gone - post-posting edit))'' ) directly between Kynde's contribution and 162.158.78.160's. Nothing in the wikicode, but I haven't looked at the HTML source yet to see what was inserted post-wikimarkup. But that wasn't what I came here to edit in.
:I was ''going'' to say that I've just bought a brand new mouse because my old wired optical mouse is flickering and failing, and I decided not to bother attacking it with a soldering iron (or at least seeing if I should). But I was disappointed to find no direct PS/2 replacement in any store, so this is USB instead. Going to try to dig up an inline USB-to-PS/2 dongle, though, and see if that works with this one's USB pinout, 'cos it's a total waste to put it through my actual USB hubstacks which are overoccupied with anything ''but'' HIDs, and asnlong as it passes the clicks and mickeys through I'd prefer my hardware to read it through that otherwise wasted venerable old port. (And if I can find a serial-to-PS/2 dongle, first, I think I have an even older device I can try, in the few days it'll take to get to the workshop where I know I'll find a proper replacement or three to try out..) So, yeah, old hardware too, was my point, somewhere in tht ramble. [[Special:Contributions/162.158.158.127|162.158.158.127]] 16:42, 29 October 2019 (UTC)
::I note that this comment section ends with a wiki tag (i.e. inside two sets of curly brackets) that says the comic's name and "/Ads", I suspect that means "Ads are allowed here in this section". Probably ExplainXKCD trying to make more revenue. As for your thing, that's what I've always hated about USB mice and keyboards, especially when they first came out. There used to be a dedicated place to plug in the mouse and keyboard, without needlessly using up a far more versatile and useful USB (the U standing for Universal, after all), and it's not like either is really optional. Though my current motherboard has USBs in that location, so I guess I can treat them as dedicated, but it doesn't feel the same. [[User:NiceGuy1|NiceGuy1]] ([[User talk:NiceGuy1|talk]]) 05:05, 1 November 2019 (UTC)
:Ad blocker? :) [[User:NiceGuy1|NiceGuy1]] ([[User talk:NiceGuy1|talk]]) 05:24, 1 November 2019 (UTC)

SNES9x is one of the main emulators of SNES hardware; since plenty of people running it are younger than an SNES would be, it seems appropriate to be the "created by". Thank you to people making emulators everywhere for helping prolong our shared childhood. (Also thanks to Vimms lair for unrelated reasons) {{unsigned|162.158.123.175}}

Actually, today's computers can take not just multiple floppy disks, but multiple CD-ROMs into RAM. Which itself is faster than it used to be. Talk about "near-instantaneously load" ... -- [[User:Hkmaly|Hkmaly]] ([[User talk:Hkmaly|talk]]) 19:26, 29 October 2019 (UTC)

[[Special:Contributions/172.68.63.5|172.68.63.5]] 20:18, 29 October 2019 (UTC) also related with these news https://www.c4isrnet.com/air/2019/10/17/the-us-nuclear-forces-dr-strangelove-era-messaging-system-finally-got-rid-of-its-floppy-disks/

Is the date on this comic accurate? A Tuesday release? [[Special:Contributions/172.69.63.75|172.69.63.75]]

:Not officially (the archive says 2019-10-28), but it did come out awfully late. The bot created the page at 11:04 pm on the 28th<s>, but I don't which timezone.</s> UTC. --[[User:Ycthiognass|Ycthiognass]] ([[User talk:Ycthiognass|talk]]) 14:39, 30 October 2019 (UTC)
:I fixed the release date in the comic header to reflect the actual Monday release instead of Tuesday. [[User:Ianrbibtitlht|Ianrbibtitlht]] ([[User talk:Ianrbibtitlht|talk]]) 14:53, 30 October 2019 (UTC)

I think the title text is just a feel-old joke and not a reference to science fiction or living in a simulation. [[Special:Contributions/108.162.216.42|108.162.216.42]] 05:56, 26 November 2020 (UTC)

Did anyone notice that the explanation says "tying into the comic's theme of a lack of unawareness that something is being digitally duplicated.", which is a double negative, which means that it does know that something is being digitally copied? [[User:Sarah the Pie(yes, the food)|Sarah the Pie(yes, the food)]] ([[User talk:Sarah the Pie(yes, the food)|talk]]) 23:15, 30 March 2021 (UTC)

SCP-079 if the researchers just gave it more memory --[[User:Öbc|Öbc]] ([[User talk:Öbc|talk]]) 21:38, 20 October 2022 (UTC)

{{Talk:2220: Imagine Going Back in Time/Ads}}

2682: Easy Or Hard

2022-10-20T21:33:58Z

Öbc: /* Transcript */ It's complete

{{comic
| number = 2682
| date = October 7, 2022
| title = Easy Or Hard
| image = easy_or_hard_2x.png
| imagesize = 740x400px
| noexpand = true
| titletext = "Friction-driven static electrification is familiar and fundamental in daily life, industry, and technology, but its basics have long been unknown and have continually perplexed scientists from ancient Greece to the high-tech era. [...] To date, no single theory can satisfactorily explain this mysterious but fundamental phenomenon." --Eui-Cheol Shin et. al. (2022)
}}

==Explanation==
{{incomplete|Created by THE EIFFEL TOWER TAKING A TYLENOL - Do NOT delete this tag too soon.}}

This comic uses a table to compare the perceived difficulty of various questions with how easily they're answered in real life. [[Randall]] has a long history of comics with similar themes, comparing perceptions to reality. In this case, both the perception and the reality are divided into three levels of difficulty, giving a total of nine categories. Accordingly three of the problems listed are effectively as difficult as one would expect, and the remaining six are not. All three of the questions whose answers are "actually pretty easy to find out" relate to the Eiffel Tower, though there's no apparent theme among the other six questions.

It's likely that this comic was at least partially inspired by writing the books ''[[How To|How To: Absurd Scientific Advice for Common Real-World Problems]]'', [[what if|''What if?'', and ''What If? 2'']], the latter of which was published just a few weeks before this comic. These books involve answering very elaborate questions from a scientific point of view. This process likely emphasized that some really strange questions are actually difficult to answer, while some questions that seem simple continue to confound scientific knowledge. ''What if? 2'' mentions the fact that no one understands why static charges separate.

{| class="wikitable"
|-
! Question !! Perceived Difficulty !! Real Difficulty !! Explanation
|-
|How tall is the Eiffel Tower?||Easy||Easy||The height of any structure that can be easily observed can be calculated without much difficulty. The Eiffel Tower was constructed to be the centerpiece of the {{w|1889 World's Fair}}. At the time of its construction, it was the tallest man-made structure on earth, which meant that its height was widely publicized since it was first constructed (312m when constructed, and now 330 meters, or 1083 feet, with the antenna added later on). This number is widely published, and easily confirmed.
* albeit with a ±6 inch differential depending on local air temperature; as the Eiffel Tower is built out of cast steel, it expands according to how much heat builds up in the metal, which in turn is derived from the intensity & daily duration of the sun's energy. It can also be argued that the number given above is due to rounding, and at sub-millimetrical lengths, the tower's exact height is fluctating constantly as a result of the aforementioned thermal expansion.
|-
|Where was Mars in the sky from Paris on the day the Eiffel Tower opened?||Difficult||Easy||The date of the opening of the tower to the public is well known (May 6, 1889). Since the motions of the planets are predictable, it's clear that calculating the answer should be possible, but it involves enough factors that one might expect it to be very difficult. However, thanks to the existence of [https://in-the-sky.org/skymap.php?no_cookie=1&latitude=48.85&longitude=2.35&timezone=1.00&year=1889&month=5&day=6&hour=9&min=0&PLlimitmag=2&zoom=182&ra=3.78242&dec=20.26465 online tools], which automatically calculate exactly this sort of thing, finding the answer is quite easy. (It was in the constellation of Taurus, and extremely close to where the Sun also was in the sky during that time so probably not easily directly observable). Alternately, to use the tools available at the time, one might check a nautical almanac for 1889, which gives the position of the major planets (and various other celestial bodies) in the sky throughout the year.
|-
|How much does the {{w|Eiffel Tower}}'s gravity deflect baseballs in Boston?||Near Impossible||Easy||This problem sounds extremely specific and esoteric, concerning an effect far too small for direct experimentation. But in theory, it's actually a very simple physics problem. {{w|Newton's law of universal gravitation|Gravitational acceleration}} is determined entirely by masses and distance, and here even the mass of the baseball can be ignored. Since the mass of the Eiffel Tower and the geographic details of both the tower in Paris and any given location in Boston (perhaps {{w|Fenway Park}}, a famous baseball stadium) are easy to look up, the calculation is quite simple.
|-
|How does {{w|general anesthesia}} work?||Easy||Difficult||While biology is always complex, inducing unconsciousness seems relatively simple. In fact, keeping a person unconscious and insensate without causing permanent damage or death is a difficult proposition, requiring a medical specialist. Despite this field being well-established, it might surprise people to know that {{w|Theories of general anaesthetic action|the mechanism of general anesthesia}} is still the subject of research, and recent studies have revealed things that we didn't previously understand.
|-
|How many ants are there?||Difficult||Difficult||While the existence of ants is a mundane part of life for many people, there are so many of them that coming up with a total number of ants in the whole world sounds exceedingly difficult. It is, in fact, a difficult problem, but experts have done a significant amount of work and have come up with well-founded estimates [https://phys.org/news/2022-09-ants-earth-quadrillion.html in the range of 20 quadrillion ants on earth].
|-
|What time of year did the Cretaceous impact happen?||Near Impossible||Difficult||The "Cretaceous impact" (the {{w|Cretaceous–Paleogene extinction event}}) happened approximately 66 million years ago. The margins of error on calculating something that ancient are necessarily thousands of years wide at least, so the notion of determining the time of year seems far-fetched. In fact, the problem is a difficult one, but many of the animals killed in the impact were fossilized, and comparing those fossils to modern-day animals at different points in their seasonal growth cycles has led to [https://www.science.org/content/article/springtime-was-season-dinosaurs-died-ancient-fish-fossils-suggest the suggestion that the impact happened in the northern-hemisphere spring.]
|-
|Why does your hair get a static charge when you rub it with a balloon?||Easy||Near Impossible||Inducing a {{w|Static electricity|static charge}} by {{w|Triboelectric effect|rubbing together two materials}} is a method that's been known since ancient times. Since human hair has a marked tendency to develop a positive charge, and the latex commonly used in balloons tends to develop a negative charge, rubbing the two together is a very simple way to create an electric field. This process is so simple that it's used for both party tricks and as a fun demonstration of electrical phenomena. Because of this simplicity, most people would assume that the phenomenon is well understood. So it's surprising that the actual mechanism remains an unsolved problem in physics. This also has previously been mentioned in [[1867: Physics Confession]]. The title text quotes [https://www.researchgate.net/publication/360674587_Derivation_of_a_governing_rule_in_triboelectric_charging_and_series_from_thermoelectricity a recent paper] explaining that, as common as this phenomenon is, there's still no theory that can adequately explain what we observe.
|-
|How does {{w|Tylenol (brand)|Tylenol}} work?||Difficult||Near Impossible||Tylenol is a brand name for {{w|Paracetamol|paracetamol, also known as acetaminophen}}, a drug commonly sold without prescription for pain relief and fever reduction. This drug has been widely used since 1950, and has been well established as being both effective and safe when used properly. Although one would expect the biological mechanism for any drug to be complicated, most people would assume that a drug that's been widely used and studied for so long to be well-documented. Surprisingly, however, the precise action still isn't fully understood. [https://medicine.tufts.edu/news-events/news/how-does-acetaminophen-work Tufts University]
|-
|How can {{w|Theory of relativity|relativity}} be reconciled with {{w|quantum mechanics}}?||Near Impossible||Near Impossible||This remains one of the {{w|Theory of everything|great unsolved questions}} in physics. The problem sounds almost unsolvable to laypeople, and remains unsolved even to experts in the field.
|}

==Transcript==
{| class="wikitable"
|-
! !! Actually pretty easy to find out !! Very hard, but there have been recent breakthroughs !! Extremely hard, currently unsolved
|-
! Sounds borderline unsolvable
|How much does the Eiffel Tower's gravity deflect baseballs in Boston?||What time of year did the cretaceous impact happen?||How can relativity be reconciled with quantum mechanics?
|-
! Sounds pretty hard, but you'd assume someone knows
|Where was Mars in the sky from Paris on the day the Eiffel Tower opened?||How many ants are there?||How does Tylenol work?
|-
! Sounds like it would be easy to look up
|How tall is the Eiffel Tower?||How does general anesthesia work?||Why does your hair get a static charge when you rub it with a balloon?
|}

{{comic discussion}}
[[Category:Charts]]
[[Category:Science]]
[[Category:Ants]]
[[Category:Medicine]]
[[Category:Physics]]
[[Category:Astronomy]]

527: Keynote

2021-04-05T15:58:30Z

Öbc: /* Explanation */

{{comic
| number = 527
| date = January 7, 2009
| title = Keynote
| image = keynote.png
| titletext = He should be better soon -- now that the Apple Store is getting rid of DRM, Cory Doctorow will get rid of his Steve Jobs voodoo doll.
}}

==Explanation==
According to this comic, {{w|Steve Jobs}}, the founder of the Apple company, lost a lot of weight due to a hormonal problem. (Though never officially confirmed, this was likely related to Jobs's battle with pancreatic cancer, which he had been fighting for years and would frequently lead to speculation about his health at the time of this comic.) [[Black Hat]] then mentions that Apple was probably excited to announce its thinnest and lightest CEO in the industry. This comment is a parody of Apple's tendency to release thinner and lighter iterations of its products. Steve Jobs' weight loss would certainly make him a thinner and lighter CEO.

The title text refers to {{w|Cory Doctorow}}, a blogger, journalist and science-fiction author. Doctorow is opposed to the technology called {{w|Digital rights management|Digital restrictions management}} (DRM for short). DRM is designed to be abused by large corporations with negative consequences for consumers, but is disguised as a copyright protection system. Randall (jokingly) proposes that Steve Jobs is only sick because Doctorow was torturing him with {{w|Voodoo doll}}s for Apple's use of DRM.

==Transcript==
:[Black Hat talking to Cueball sitting at computer.]
:Cueball: Huh - Steve Jobs isn't doing a keynote this year, citing massive weight loss due to some hormonal problem.
:Black Hat: Too bad. I bet Apple was excited about unveiling the thinnest and lightest CEO in the industry.

==Trivia==
Steve Jobs died on October 5, 2011 of pancreatic cancer the day before [[Randall]] released [[961: Eternal Flame]]. Presumably, the cancer was the cause of Jobs' weight loss, although it was not public information at the time the comic was posted.

{{comic discussion}}
[[Category:Comics featuring Black Hat]]
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Steve Jobs]]
[[Category:Sarcasm]]
[[Category:Comics featuring Cory Doctorow]]

1481: API

2021-03-15T12:40:29Z

Öbc: /* Explanation */

{{comic
| number = 1481
| date = February 2, 2015
| title = API
| image = api.png
| titletext = ACCESS LIMITS: Clients may maintain connections to the server for no more than 86,400 seconds per day. If you need additional time, you may contact IERS to file a request for up to one additional second.
}}

==Explanation==
This comic presents a web site designed for human readers as if it had an API ({{w|application programming interface}}) designed for machine-to-machine {{w|web service}}. An API is a set of instructions about a computer program, intended to be used by developers of other computer programs, so the two programs can interoperate more easily. The documentation explains how to send commands to the program, and how the output will be returned.

Many web APIs are designed to return data in {{w|XML}} format. But in this case, the XML is {{w|XHTML}}, a version of the language that is used by most web pages. The "requested data" is the actual content (e.g. a blog post), and "documentation" refers (in an obscure way) to the parts of a web page that control how it looks on the screen (e.g. {{w|Cascading_Style_Sheets|CSS}} and perhaps JavaScript layout code). The
"documentation" may also be {{w|DTD}} which tells the XML parser info about this particular {{w|XML}} format, i.e. XHTML.

In order for a program to process a generic web site designed for human viewing, the program needs to use {{w|web scraping}} techniques, which often break when the web site design changes in subtle ways that a human might never notice. Therefore, developers [http://www.rubyinside.com/ruby-gets-a-stylish-html-scraper-scrapi-140.html prefer to have proper APIs] with well-defined machine-readable formats, stable interfaces and documentation that actually describes the semantics of the data.

For example, Google has an [https://developers.google.com/youtube/v3/getting-started official API for version 3 of their Youtube web service]. But developers who don't want to hassle with the required API key or the costs associated with its use sometimes just [http://stackoverflow.com/questions/20407107/scraping-youtube-mix-playlist-id-for-a-video scrape the regular YouTube web site]. So someone could publish this comic with a YouTube URL as a convoluted hint to developers that there is an alternative to the official API.

The API keys section is a step-by-step description of how a web page is protected with {{w|HTTP Secure}} (HTTPS). The {{w|Transport Layer Security}} (TLS) protocol uses an {{w|elliptic curve Diffie–Hellman}} (ECDH) key signed using {{w|Rivest-Shamir-Adleman}} (RSA) encryption, which is stored in an {{w|X.509}} certificate. Normally, the browser or operating system does this behind the scenes, so most web developers and users do not need to know these details.

The access limits mentioned in the title text says that the API can be used for 86,400 seconds each day. At first this may appear to be a strange arbitrary number, however it is in fact the total number of seconds in 24 hours, essentially meaning there is no limit on most days. The {{w|International Earth Rotation and Reference Systems Service}} (IERS) is the organization that decides when to add {{w|leap seconds}}, which account for slight anomalies in the Earth's rotation as compared to the {{w|mean solar day}}. These leap seconds will mean that the website is available for one extra second occasionally, although IERS decisions are based on actual Earth rotation rates and they of course wouldn't respond to requests for leap seconds in order to lengthen the number of seconds that a web site would be available for in a given calendar day. The API does not discuss the issue that some days have 23 or 25 hours due to {{w|Daylight saving time|daylight saving time}} in the U.S. and {{w|Summer time|summer time}} in Europe and some other places. This suggests that the web service tracks time via {{w|UTC}}.

==Transcript==
:[Cueball sitting at a desk staring at a computer screen.]
:<big>'''API Guide'''</big>
:Request URL format:
:<nowiki>http://~~~.com/<username>/<item ID> </nowiki>

:Server will return an XML document which contains:
:*The requested data.
:*Documentation describing how the data is organized spatially.

:;API Keys
:To obtain API access, contact the X.509-authenticated server and request an ECDH-RSA TLS key...
:<hr/>
:If you do things right, it can take people a while to realize that your "API documentation" is just instructions for how to look at your website.

{{comic discussion}}
[[Category:Comics featuring Cueball]]
[[Category:Programming]]
[[Category:Time]]