# ­xkcd thread **URL:** \ **Category:** Cafe Society\ **Tags:** comic-strips\ **Created:** [May 28, 2020, 12:57am UTC](https://boards.straightdope.com/t/xkcd-thread/854574 "2020-05-28T00:57:03Z")\ **Posts on this page:** 20\ **Page:** 211
**Author:** ![Alessan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/alessan/32/465_2.png) [@Alessan](https://boards.straightdope.com/u/Alessan)\ **Post date:** [April 17, 2025, 2:15pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4203 "2025-04-17T14:15:13Z")
OK, I’m going to need an explanation for this one. ---
**Author:** ![Pardel-Lux](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pardel-lux/32/20182_2.png) [@Pardel-Lux](https://boards.straightdope.com/u/Pardel-Lux)\ **Post date:** [April 17, 2025, 2:23pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4204 "2025-04-17T14:23:19Z")
I have the impression you are going to love the wikiarticle on De Sitter spaces: > **[De Sitter space](https://en.wikipedia.org/wiki/De_Sitter_space)** > > In mathematical physics, n-dimensional de Sitter space (often denoted dSn) is a maximally symmetric Lorentzian manifold with constant positive scalar curvature. It is the Lorentzian\[further explanation needed\] analogue of an n-sphere (with its canonical Riemannian metric). > The main application of de Sitter space is its use in general relativity, where it serves as one of the simplest mathematical models of the universe consistent with the observed accelerating expansion of the universe. More sp... I did, and I did not understand a single sentence! ETA: The [further explanation needed] note is so sweet! ---
**Author:** ![Alessan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/alessan/32/465_2.png) [@Alessan](https://boards.straightdope.com/u/Alessan)\ **Post date:** [April 17, 2025, 2:24pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4205 "2025-04-17T14:24:30Z")
I already tried to read it. Why do you think I asked for help? ---
**Author:** ![smithsb](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/smithsb/32/12107_2.png) [@smithsb](https://boards.straightdope.com/u/smithsb)\ **Post date:** [April 17, 2025, 2:28pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4206 "2025-04-17T14:28:27Z")
Are we talking spherical cow here? (Pinning for the next xkcd post I _might_ understand) ---
**Author:** ![Pleonast](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pleonast/32/1183_2.png) [@Pleonast](https://boards.straightdope.com/u/Pleonast)\ **Post date:** [April 17, 2025, 2:31pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4207 "2025-04-17T14:31:28Z")
It’s a riff on the mathematical constructs of [De Sitter space](https://en.wikipedia.org/wiki/De_Sitter_space) and [Anti-de Sitter space](https://en.wikipedia.org/wiki/Anti-de_Sitter_space). They’re multi-dimensional versions of a sphere and a hyperboloid. To explain in very simple terms: _Euclidean space_ has zero curvature. Think of your basic flat plane. The sum of the interior angles of a triangle will always be exactly 180 degrees. _De Sitter space_ has positive curvature. Think of your basic spherical surface. The sum of the interior angles of a triangle will always be greater than 180 degrees. _Anti-de Sitter space_ has negative curvature. Think of the bell of a trumpet or a saddle. The sum of the interior angles of a triangle will always be less than 180 degrees. Physicists use these things as simplifications of a general metric tensor, where the curvature is not constrained at all. ---
**Author:** ![Tatterdemalion](https://avatars.discourse-cdn.com/v4/letter/t/43a26b/32.png) [@Tatterdemalion](https://boards.straightdope.com/u/Tatterdemalion)\ **Post date:** [April 17, 2025, 3:32pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4208 "2025-04-17T15:32:21Z")
I read the XKCD explains site, and I still don’t understand it. I wonder if he isn’t just making a joke about how none of the walls in his house are square and parallel, and none of the angles add up correctly. It certainly describes my house. ---
**Author:** ![Yllaria](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yllaria/32/3452_2.png) [@Yllaria](https://boards.straightdope.com/u/Yllaria)\ **Post date:** [April 17, 2025, 5:48pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4209 "2025-04-17T17:48:50Z")
I may understand if I let it sit and perk for awhile. In the meantime, the sign on the door makes me think of [Henry Symeonis](https://www.loweringthebar.net/2024/01/i-hereby-swear-to-hate-henry-symeonis.html). ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [April 17, 2025, 5:58pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4210 "2025-04-17T17:58:56Z")
> [@Pleonast](#): > > _Anti-de Sitter space_ has negative curvature. Think of the bell of a trumpet or a saddle. Or some of MC Escher’s work: [![](https://mathandart.com/static/f777b61c268a9b4547ad05fa8cd277b3/b4294/escher_circle_limit_i.jpg) ](https://mathandart.com/static/f777b61c268a9b4547ad05fa8cd277b3/b4294/escher_circle_limit_i.jpg) > [@Tatterdemalion](#): > > I wonder if he isn’t just making a joke about how none of the walls in his house are square and parallel, and none of the angles add up correctly. No, it’s just that _anti-de Sitter space_ is a funny phrase, because it sounds like it’s against that de Sitter guy, as opposed to the opposite of the mathematical construct he came up with. ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [April 17, 2025, 6:01pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4211 "2025-04-17T18:01:10Z")
Mathematicians love how tractable problems in physics become in anti-de Sitter space; too bad that we’re virtually certain that it isn’t a description of our actual physical universe. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [April 17, 2025, 6:02pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4212 "2025-04-17T18:02:56Z")
More to the point, de Sitter space and anti-de Sitter space both have a cosmological constant (positive in the former case and negative in the latter), but no matter. ---
**Author:** ![TroutMan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/troutman/32/6721_2.png) [@TroutMan](https://boards.straightdope.com/u/TroutMan)\ **Post date:** [April 17, 2025, 6:33pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4213 "2025-04-17T18:33:58Z")
Physicists have a different definition of “to the point” than most people. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [April 19, 2025, 2:58am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4214 "2025-04-19T02:58:40Z")
> **[Anchor Screws](https://xkcd.com/3078/)** [![](https://imgs.xkcd.com/comics/anchor_screws.png) ](https://imgs.xkcd.com/comics/anchor_screws.png) “The biggest expense was installing the mantle ducts to keep the carbonate-silicate cycle operating.” ---
**Author:** ![RivkahChaya](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rivkahchaya/32/8919_2.png) [@RivkahChaya](https://boards.straightdope.com/u/RivkahChaya)\ **Post date:** [April 19, 2025, 2:35pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4215 "2025-04-19T14:35:38Z")
> [@puzzlegal](#): > > I feel like that’s a different kind of error. As you say, it was introduced purely mechanically, and not by human misunderstanding. And it’s often quite obvious when it occurs. I majored in English. Scribes were always dropping their pages, or just losing their place, and then someone ends up married to his daughter. And it’s not obvious to the next scribe, who tries to retrofit it, by saying that such things used to be common, or that it was really his stepdaughter. ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [April 19, 2025, 4:29pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4216 "2025-04-19T16:29:10Z")
Keep putting new anchors in and after a few hundred million years the NW coast of the US is hundreds of miles further west. I guess you can say that the owners of former shoreline property got screwed. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [April 19, 2025, 7:25pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4217 "2025-04-19T19:25:51Z")
Yes. But America will be bigger and that’s all that matters. To some people. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [April 21, 2025, 3:20pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4218 "2025-04-21T15:20:37Z")
> **[Air Fact](https://xkcd.com/3079/)** [![](https://imgs.xkcd.com/comics/air_fact.png) ](https://imgs.xkcd.com/comics/air_fact.png) “‘Wow, that must be why you swallow so many of them per year!’ ‘No, that’s spiders. You swallow WAY more ants.’” ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [April 24, 2025, 3:24am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4219 "2025-04-24T03:24:28Z")
> **[Tennis Balls](https://xkcd.com/3080/)** [![](https://imgs.xkcd.com/comics/tennis_balls.png) ](https://imgs.xkcd.com/comics/tennis_balls.png) “After initial tests created a series of large holes in the wall of the lab, the higher-power Scanning Tunneling Tennis Ball Microscope project was quickly shut down.” ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [April 25, 2025, 11:06pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4220 "2025-04-25T23:06:59Z")
> **[PhD Timeline](https://xkcd.com/3081/)** [![](https://imgs.xkcd.com/comics/phd_timeline.png) ](https://imgs.xkcd.com/comics/phd_timeline.png) “Rümeysa Öztürk was grabbed off the street in my town one month ago.” ---
**Author:** ![TroutMan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/troutman/32/6721_2.png) [@TroutMan](https://boards.straightdope.com/u/TroutMan)\ **Post date:** [April 26, 2025, 12:07am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4221 "2025-04-26T00:07:43Z")
Oh wait, this one’s not a joke. What a fucked up timeline. ---
**Author:** ![puzzlegal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/puzzlegal/32/3827_2.png) [@puzzlegal](https://boards.straightdope.com/u/puzzlegal)\ **Post date:** [April 26, 2025, 2:49pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4222 "2025-04-26T14:49:20Z")
Yeah, maybe the least funny XKCD I’ve ever read. 😢 [Previous page](https://boards.straightdope.com/t/xkcd-thread/854574.md?page=210) [Next page](https://boards.straightdope.com/t/xkcd-thread/854574.md?page=212)