Talk:3077: de Sitter - Revision history

Dextrous Fred: Appreciation

2025-04-24T19:44:58Z

Appreciation

162.158.216.56: Tidy-up of obvious part-/un-signed bits

2025-04-23T15:35:06Z

Tidy-up of obvious part-/un-signed bits

Kurahaupo at 10:14, 23 April 2025

2025-04-23T10:14:06Z

172.71.151.156: Explain the joke part

2025-04-23T01:14:47Z

Explain the joke part

172.70.91.11 at 08:32, 22 April 2025

2025-04-22T08:32:33Z

172.70.86.129 at 08:29, 22 April 2025

2025-04-22T08:29:08Z

172.70.160.196 at 08:25, 22 April 2025

2025-04-22T08:25:23Z

Trimutius at 14:07, 18 April 2025

2025-04-18T14:07:02Z

Trimutius at 14:06, 18 April 2025

2025-04-18T14:06:39Z

162.158.103.102 at 11:18, 18 April 2025

2025-04-18T11:18:35Z

← Older revision		Revision as of 19:44, 24 April 2025
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	I'm a chemist. Mr. Markovnikov shouldn't appear near my house! [[Special:Contributions/162.158.103.102\|162.158.103.102]] 11:18, 18 April 2025 (UTC)		I'm a chemist. Mr. Markovnikov shouldn't appear near my house! [[Special:Contributions/162.158.103.102\|162.158.103.102]] 11:18, 18 April 2025 (UTC)
		+	:I understood that reference. Thank you [[User:Dextrous Fred\|Dextrous Fred]] ([[User talk:Dextrous Fred\|talk]]) 19:44, 24 April 2025 (UTC)

	i think the joke is that his house is a Euclidian space. Because he wants all triangles to add up to 180 degrees and 2 parallel lines to never meet.		i think the joke is that his house is a Euclidian space. Because he wants all triangles to add up to 180 degrees and 2 parallel lines to never meet.

@@ Line 12: / Line 12: @@
 Fun Fact: the german version of Anti-de Sitter space in wikipedia refers to a [Randall–Sundrum model|https://en.wikipedia.org/wiki/Randall%E2%80%93Sundrum_model] {{unsigned ip|172.69.150.119|09:20, 17 April 2025 (UTC)}}
-i think the joke is that his house is a Euclidian space. Because he wants all triangles to add up to 180 degrees and 2 parallel lines to never meet.
+"...less than 180° in a full rotation" - Shouldn't this be either "...less than 360° in a full rotation" (or perhaps "...the angles of a triangle add up to less than 180°"). [[Special:Contributions/172.69.186.206|172.69.186.206]] 09:53, 17 April 2025 (UTC)
-Basically he just wants his house to function normally, not fall down, and have regular corners
+I've started to explain the title-text, but not well. I don't really understand either of these concepts. {{unsigned|Xnerkcd|10:01, 17 April 2025 (UTC)}}
-"...less than 180° in a full rotation" - Shouldn't this be either "...less than 360° in a full rotation" (or perhaps "...the angles of a triangle add up to less than 180°"). [[Special:Contributions/172.69.186.206|172.69.186.206]]
+I don’t really know how to explain it well, but the wikipedia page on these spaces says it’s negative SCALAR curvature. That is a different concept from what is currently being explained here. The intuitive dimension of curvature applies only to 2-dimensional spaces. In higher dimensions you can look at 2D-slices, and the curvature of those is called the sectional curvature. Scalar curvature is then something of an average of those. Notably, if scalar curvature is negative, that does not mean sectional curvature necessarily always is (though perhaps the higher symmetry of these spaces enforces this? I’m really not sure). The main way you can measure scalar curvature is by calculating the volume of a sphere of radius r – if the scalar curvature is 0 it’ll be the usual formula from Euclidean space, but if it’s negative, then for sufficiently small radii the volume will be bigger than expected (intuitively, more space gets crammed around each point). Feel free to incorporate this into the article. {{unsigned ip|172.69.225.250|10:30, 17 April 2025}}
 I thought it might be a play on "housesitter" and the fact that anti and de can denote negatives, but I'm not sure how [[User:BeeVee|BeeVee]] ([[User talk:BeeVee|talk]]) 14:37, 17 April 2025 (UTC)
@@ Line 39: / Line 35: @@
 I'm a chemist. Mr. Markovnikov shouldn't appear near my house! [[Special:Contributions/162.158.103.102|162.158.103.102]] 11:18, 18 April 2025 (UTC)
-----
+i think the joke is that his house is a Euclidian space. Because he wants all triangles to add up to 180 degrees and 2 parallel lines to never meet.
 I've added a leading paragraph with some background for non-mathematicians, and swapped the order of the definitions for ''de Sitter space'' and ''anti de Sitter space''. Hopefully that resolves the '''incomplete''' tag; if you agree, please remove the tag.
-[[User:Kurahaupo|Kurahaupo]] ([[User talk:Kurahaupo|talk]])
+[[User:Kurahaupo|Kurahaupo]] ([[User talk:Kurahaupo|talk]]) 10:14, 23 April 2025 (UTC)

← Older revision		Revision as of 10:14, 23 April 2025
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	I'm a chemist. Mr. Markovnikov shouldn't appear near my house! [[Special:Contributions/162.158.103.102\|162.158.103.102]] 11:18, 18 April 2025 (UTC)		I'm a chemist. Mr. Markovnikov shouldn't appear near my house! [[Special:Contributions/162.158.103.102\|162.158.103.102]] 11:18, 18 April 2025 (UTC)
		+
		+	----
		+	I've added a leading paragraph with some background for non-mathematicians, and swapped the order of the definitions for ''de Sitter space'' and ''anti de Sitter space''. Hopefully that resolves the '''incomplete''' tag; if you agree, please remove the tag.
		+	[[User:Kurahaupo\|Kurahaupo]] ([[User talk:Kurahaupo\|talk]])

← Older revision		Revision as of 01:14, 23 April 2025
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	Fun Fact: the german version of Anti-de Sitter space in wikipedia refers to a [Randall–Sundrum model\|https://en.wikipedia.org/wiki/Randall%E2%80%93Sundrum_model] {{unsigned ip\|172.69.150.119\|09:20, 17 April 2025 (UTC)}}		Fun Fact: the german version of Anti-de Sitter space in wikipedia refers to a [Randall–Sundrum model\|https://en.wikipedia.org/wiki/Randall%E2%80%93Sundrum_model] {{unsigned ip\|172.69.150.119\|09:20, 17 April 2025 (UTC)}}
		+
		+	i think the joke is that his house is a Euclidian space. Because he wants all triangles to add up to 180 degrees and 2 parallel lines to never meet.
		+
		+	Basically he just wants his house to function normally, not fall down, and have regular corners

	"...less than 180° in a full rotation" - Shouldn't this be either "...less than 360° in a full rotation" (or perhaps "...the angles of a triangle add up to less than 180°"). [[Special:Contributions/172.69.186.206\|172.69.186.206]]		"...less than 180° in a full rotation" - Shouldn't this be either "...less than 360° in a full rotation" (or perhaps "...the angles of a triangle add up to less than 180°"). [[Special:Contributions/172.69.186.206\|172.69.186.206]]

@@ Line 10: / Line 10: @@
 maybe a pun on "babysitters are not welcome here" [[User:Translated ORK|Translated ORK]] ([[User talk:Translated ORK|talk]]) 09:08, 17 April 2025 (UTC)
-Fun Fact: the german version of Anti-de Sitter space in wikipedia refers to a [Randall–Sundrum model|https://en.wikipedia.org/wiki/Randall%E2%80%93Sundrum_model]
+Fun Fact: the german version of Anti-de Sitter space in wikipedia refers to a [Randall–Sundrum model|https://en.wikipedia.org/wiki/Randall%E2%80%93Sundrum_model] {{unsigned ip|172.69.150.119|09:20, 17 April 2025 (UTC)}}
 "...less than 180° in a full rotation" - Shouldn't this be either "...less than 360° in a full rotation" (or perhaps "...the angles of a triangle add up to less than 180°"). [[Special:Contributions/172.69.186.206|172.69.186.206]]
-I've started to explain the title-text, but not well. I don't really understand either of these concepts.
+I've started to explain the title-text, but not well. I don't really understand either of these concepts. {{unsigned|Xnerkcd|17 April 2025 (UTC)}}
 I don’t really know how to explain it well, but the wikipedia page on these spaces says it’s negative SCALAR curvature. That is a different concept from what is currently being explained here. The intuitive dimension of curvature applies only to 2-dimensional spaces. In higher dimensions you can look at 2D-slices, and the curvature of those is called the sectional curvature. Scalar curvature is then something of an average of those. Notably, if scalar curvature is negative, that does not mean sectional curvature necessarily always is (though perhaps the higher symmetry of these spaces enforces this? I’m really not sure). The main way you can measure scalar curvature is by calculating the volume of a sphere of radius r – if the scalar curvature is 0 it’ll be the usual formula from Euclidean space, but if it’s negative, then for sufficiently small radii the volume will be bigger than expected (intuitively, more space gets crammed around each point). Feel free to incorporate this into the article.

@@ Line 20: / Line 20: @@
 I thought it might be a play on "housesitter" and the fact that anti and de can denote negatives, but I'm not sure how [[User:BeeVee|BeeVee]] ([[User talk:BeeVee|talk]]) 14:37, 17 April 2025 (UTC)
-This seems too well-timed to not reference Idaho's Everyone is Welcome Here controversy.
+This seems too well-timed to not reference Idaho's Everyone is Welcome Here controversy. {{unsigned ip|172.68.35.117|15:57, 17 April 2025 (UTC)}}
 Is this the first strip where the title begins with a lower-case letter? Also, I just noticed that the site's strips use small-caps, while this site uses traditional case. Is that something worth examining? [[Special:Contributions/172.71.98.3|172.71.98.3]] 15:03, 17 April 2025 (UTC)

@@ Line 35: / Line 35: @@
 :Draw them on a sphere (i.e., a space with positive curvature, a.k.a. a de Sitter space) and they do. The canonical example of this is the lines of longitude on the Earth, which really are parallel at the equator and yet definitely meet at the poles. --[[Special:Contributions/172.68.205.150|172.68.205.150]] 07:50, 18 April 2025 (UTC)
 ::I think the point being that they aren't parallel lines if they do meet, they (just like on hyperbolic planes) have points where a line that crosses both does so at 90° to each. By the parallel postulate, there are no possible parallel lines (geodesics) in spherical geometry, though there are parallel-line surrogates (the parallel curves of lines of latitude, for example) that obey a looser interpretation. [[Special:Contributions/172.71.26.106|172.71.26.106]] 10:15, 18 April 2025 (UTC)
-::yes on a sphere you can have triangle made out of 3 right angles... Is it made out of three parallel lines? Of course not, at least that is not how mathematicians treat it... The proper replacement of parallel line postulate in de Sitter space is that all lines intersect, so there is no parallel lines...
+::Yes on a sphere you can have triangle made out of 3 right angles... Is it made out of three parallel lines? Of course not, at least that is not how mathematicians treat it... The proper replacement of parallel line postulate in de Sitter space is that all lines intersect, so there is no parallel lines... --[[User:Trimutius|Trimutius]] ([[User talk:Trimutius|talk]]) 14:07, 18 April 2025 (UTC)
 I'm a chemist. Mr. Markovnikov shouldn't appear near my house! [[Special:Contributions/162.158.103.102|162.158.103.102]] 11:18, 18 April 2025 (UTC)

← Older revision		Revision as of 11:18, 18 April 2025
Line 35:		Line 35:
	:Draw them on a sphere (i.e., a space with positive curvature, a.k.a. a de Sitter space) and they do. The canonical example of this is the lines of longitude on the Earth, which really are parallel at the equator and yet definitely meet at the poles. --[[Special:Contributions/172.68.205.150\|172.68.205.150]] 07:50, 18 April 2025 (UTC)		:Draw them on a sphere (i.e., a space with positive curvature, a.k.a. a de Sitter space) and they do. The canonical example of this is the lines of longitude on the Earth, which really are parallel at the equator and yet definitely meet at the poles. --[[Special:Contributions/172.68.205.150\|172.68.205.150]] 07:50, 18 April 2025 (UTC)
	::I think the point being that they aren't parallel lines if they do meet, they (just like on hyperbolic planes) have points where a line that crosses both does so at 90° to each. By the parallel postulate, there are no possible parallel lines (geodesics) in spherical geometry, though there are parallel-line surrogates (the parallel curves of lines of latitude, for example) that obey a looser interpretation. [[Special:Contributions/172.71.26.106\|172.71.26.106]] 10:15, 18 April 2025 (UTC)		::I think the point being that they aren't parallel lines if they do meet, they (just like on hyperbolic planes) have points where a line that crosses both does so at 90° to each. By the parallel postulate, there are no possible parallel lines (geodesics) in spherical geometry, though there are parallel-line surrogates (the parallel curves of lines of latitude, for example) that obey a looser interpretation. [[Special:Contributions/172.71.26.106\|172.71.26.106]] 10:15, 18 April 2025 (UTC)
		+
		+	I'm a chemist. Mr. Markovnikov shouldn't appear near my house! [[Special:Contributions/162.158.103.102\|162.158.103.102]] 11:18, 18 April 2025 (UTC)