![]() | Flatness problem was a Natural sciences good articles nominee, but did not meet the good article criteria at the time. There may be suggestions below for improving the article. Once these issues have been addressed, the article can be renominated. Editors may also seek a reassessment of the decision if they believe there was a mistake. | |||||||||
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![]() | A fact from this article appeared on Wikipedia's
Main Page in the "
Did you know?" column on
September 14, 2008. The text of the entry was: Did you know ... that
cosmologists
C. B. Collins and
Stephen Hawking proposed an
infinite number of universes to explain the
Flatness problem in the
curvature of spacetime (three possibilities pictured)? |
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Okay, here's something I ought to understand but don't, and would like some clarification of.
This value of 1x10^-29 g/cm presumably must either be a function of time, or rather of the size of the universe, or be measured in some sort of co-moving coordinate system in which a cm today is larger than a cm yesterday, right? Otherwise, if the density were slightly above 1x10^-29 g/cm early in the history of the universe, it would fall below that value as the universe expands, and you'd go from a universe that's supposed to fall back into a big crunch to a universe that is supposed to expand forever, and that makes no sense.
Is it the case that in a matter dominated universe, Ω is constant? If it isn't, how can it vary? And in a universe with dark matter, Ω does evolve... right? -- Rsholmes 18:40, 20 February 2006 (UTC)
I'm glad to see some work being done on this article. I'd still like to better understand the evolution of Ω. In universe without dark energy / cosmological constant, is Ω constant in time? It would seem as though the answer must be no, and the article seems to suggest that. But what is the mechanism for this evolution? -- Rsholmes 23:46, 22 December 2006 (UTC)
I've just done a complete rewrite of the article I'd been working on in user space for a while. There are still some things left on my to-do list, but it seemed ready for mainspace. Here are some things I'll try and work on - feel free to give a hand!
Olaf Davis | Talk 11:21, 7 September 2008 (UTC)
This article is a good attempt at explaining a rather esoteric problem to a general audience but it has a few major problems. First (and this is the root of the other problems), it is too short to cover the subject appropriately. Second, it doesn't provide sufficient context for the subject. I can't judge the article POV because I have little information about the history of the problem among the community of physicists and the status of the solutions among the same. Third, the article has a spotty expectation of reader familiarity of the subject. Let's take these one by one:
I'm going to place this article on hold. The problems this article has to overcome are significant but not insurmountable. If they aren't one in ~7 days, no one should be ashamed if this article is not listed. The problems can be fixed and this article will be a GA soon. If not in the next seven days than soon thereafter. Thanks for giving me the chance to review an article like this. Protonk ( talk) 03:47, 9 September 2008 (UTC)
I know there is no rush, but holding this article for 15 days is a little much. I would probably feel differently if the issues were being actively addressed, but it has been 9 days since the last change to the article. This article has a lot of potential but it isn't a good article yet. If you disagree with this decision feel free to post here or on my talk page. If you feel it was flagrantly unacceptable, you may bring this article to Good Article Review. Thank you and better luck in the future. Protonk ( talk) 04:34, 25 September 2008 (UTC)
Originally, the article stated that:
Data from the Wilkinson Microwave Anisotropy Probe (measuring CMB anisotropies) combined with that from the Sloan Digital Sky Survey (observing Ia supernovae) constrain Ω0 to be 1 within 1%.
This is misleading because the main contribution of SDSS to measuring the spatial flatness is through the galaxy power spectrum and it is this data that was used in the study cited. Although, as Olaf Davis pointed out in his edit summary, the SDSS telescope has been used more recently to find type-1a supernovae [3], this data was not used in the study cited. Even if it had been, it would be misleading to single it out for mention, since the Sloan Supernova Survey data form only a part of the overall sample of supernovae with measured redshifts.
I changed the above sentence to read:
Data from the Wilkinson Microwave Anisotropy Probe (measuring CMB anisotropies) combined with that from the Sloan Digital Sky Survey and observations of type-Ia supernovae constrain Ω0 to be 1 within 1%.
I think this is a more accurate description - at least of the study cited. I'll admit to being out of the loop for the past year though, so if anyone knows of a more recent study in which spatial flatness has been measured to a higher degree of accuracy using only WMAP data and type-1a supernovae, then please update the citation.
Cosmo0 ( talk) 22:52, 15 September 2009 (UTC)
The first diagram that shows three different geometries based on curvature: positive, negative and flat. For each of these geometries, a triangle is shown. The triangle for the negative curvature is wrong. The sum of the degrees for the three angles in a triangle on these three geometric surfaces should be respectively: >180, <180, =180. The triangle shown for the negative curvature erroneously has a angles adding to >180, like the positive curvature triangle. BuzzBloom ( talk) 13:34, 17 March 2015 (UTC) BuzzBloom
Universal flatness is the law. Other artefacts are secondary. All the data suggest that the universal flatness is fundamental.Dark Matter, Dark Energy and Big Bangs are secondary effects that urge to maintain that permanent flatness. Some people like mistakes because are weird. A mistake is always stupid and against the data though. — Preceding unsigned comment added by 2A02:587:4103:AE00:D47:B687:8172:7D1E ( talk) 23:13, 1 July 2016 (UTC)
How about a section exploring the possible solutions if we relax the Copernican Principle? — Preceding unsigned comment added by 157.14.234.194 ( talk) 11:11, 6 April 2019 (UTC)
Just read some old comments about the status of the article and so on. No offense, but if one isn't sure whether Omega is constant in time (in general, it is not), should one even attempt writing such an article?
This is an important problem (or lack of a problem, since current research suggests that it is based on a misunderstanding), but even most people who work broadly within the field of cosmology don't understand it, much less astrophysicists in general, much less scientists in general, much less the general public. — Preceding unsigned comment added by 193.29.81.233 ( talk) 11:40, 17 March 2020 (UTC)
What I don't understand at this flatness problem is that on one hand the universe seems to be flat today. Most cosmologist would indeed prefer this case. But if it is really flat it must have been so since the big bang because in this case omega needs to be the exact integer 1 and thereby would never deviate from that number (zero deviation from 1 cannot be inflated). If, for instance, the universe was spherically closed since the beginning, the observable universe also tends to increasingly getting flat like the limited surface on an inflating balloon. In that case omega only gets close to 1 but always deviates from 1 by some error. So what's the problem? Is it considered that it is highly improbable that nature started with an exact integer for omega? Is that the problem? Please explain! EternalAsker ( talk) 18:31, 20 July 2023 (UTC)
![]() | Flatness problem was a Natural sciences good articles nominee, but did not meet the good article criteria at the time. There may be suggestions below for improving the article. Once these issues have been addressed, the article can be renominated. Editors may also seek a reassessment of the decision if they believe there was a mistake. | |||||||||
| ||||||||||
![]() | A fact from this article appeared on Wikipedia's
Main Page in the "
Did you know?" column on
September 14, 2008. The text of the entry was: Did you know ... that
cosmologists
C. B. Collins and
Stephen Hawking proposed an
infinite number of universes to explain the
Flatness problem in the
curvature of spacetime (three possibilities pictured)? |
![]() | This ![]() It is of interest to the following WikiProjects: | |||||||||||||||||||||||
|
Okay, here's something I ought to understand but don't, and would like some clarification of.
This value of 1x10^-29 g/cm presumably must either be a function of time, or rather of the size of the universe, or be measured in some sort of co-moving coordinate system in which a cm today is larger than a cm yesterday, right? Otherwise, if the density were slightly above 1x10^-29 g/cm early in the history of the universe, it would fall below that value as the universe expands, and you'd go from a universe that's supposed to fall back into a big crunch to a universe that is supposed to expand forever, and that makes no sense.
Is it the case that in a matter dominated universe, Ω is constant? If it isn't, how can it vary? And in a universe with dark matter, Ω does evolve... right? -- Rsholmes 18:40, 20 February 2006 (UTC)
I'm glad to see some work being done on this article. I'd still like to better understand the evolution of Ω. In universe without dark energy / cosmological constant, is Ω constant in time? It would seem as though the answer must be no, and the article seems to suggest that. But what is the mechanism for this evolution? -- Rsholmes 23:46, 22 December 2006 (UTC)
I've just done a complete rewrite of the article I'd been working on in user space for a while. There are still some things left on my to-do list, but it seemed ready for mainspace. Here are some things I'll try and work on - feel free to give a hand!
Olaf Davis | Talk 11:21, 7 September 2008 (UTC)
This article is a good attempt at explaining a rather esoteric problem to a general audience but it has a few major problems. First (and this is the root of the other problems), it is too short to cover the subject appropriately. Second, it doesn't provide sufficient context for the subject. I can't judge the article POV because I have little information about the history of the problem among the community of physicists and the status of the solutions among the same. Third, the article has a spotty expectation of reader familiarity of the subject. Let's take these one by one:
I'm going to place this article on hold. The problems this article has to overcome are significant but not insurmountable. If they aren't one in ~7 days, no one should be ashamed if this article is not listed. The problems can be fixed and this article will be a GA soon. If not in the next seven days than soon thereafter. Thanks for giving me the chance to review an article like this. Protonk ( talk) 03:47, 9 September 2008 (UTC)
I know there is no rush, but holding this article for 15 days is a little much. I would probably feel differently if the issues were being actively addressed, but it has been 9 days since the last change to the article. This article has a lot of potential but it isn't a good article yet. If you disagree with this decision feel free to post here or on my talk page. If you feel it was flagrantly unacceptable, you may bring this article to Good Article Review. Thank you and better luck in the future. Protonk ( talk) 04:34, 25 September 2008 (UTC)
Originally, the article stated that:
Data from the Wilkinson Microwave Anisotropy Probe (measuring CMB anisotropies) combined with that from the Sloan Digital Sky Survey (observing Ia supernovae) constrain Ω0 to be 1 within 1%.
This is misleading because the main contribution of SDSS to measuring the spatial flatness is through the galaxy power spectrum and it is this data that was used in the study cited. Although, as Olaf Davis pointed out in his edit summary, the SDSS telescope has been used more recently to find type-1a supernovae [3], this data was not used in the study cited. Even if it had been, it would be misleading to single it out for mention, since the Sloan Supernova Survey data form only a part of the overall sample of supernovae with measured redshifts.
I changed the above sentence to read:
Data from the Wilkinson Microwave Anisotropy Probe (measuring CMB anisotropies) combined with that from the Sloan Digital Sky Survey and observations of type-Ia supernovae constrain Ω0 to be 1 within 1%.
I think this is a more accurate description - at least of the study cited. I'll admit to being out of the loop for the past year though, so if anyone knows of a more recent study in which spatial flatness has been measured to a higher degree of accuracy using only WMAP data and type-1a supernovae, then please update the citation.
Cosmo0 ( talk) 22:52, 15 September 2009 (UTC)
The first diagram that shows three different geometries based on curvature: positive, negative and flat. For each of these geometries, a triangle is shown. The triangle for the negative curvature is wrong. The sum of the degrees for the three angles in a triangle on these three geometric surfaces should be respectively: >180, <180, =180. The triangle shown for the negative curvature erroneously has a angles adding to >180, like the positive curvature triangle. BuzzBloom ( talk) 13:34, 17 March 2015 (UTC) BuzzBloom
Universal flatness is the law. Other artefacts are secondary. All the data suggest that the universal flatness is fundamental.Dark Matter, Dark Energy and Big Bangs are secondary effects that urge to maintain that permanent flatness. Some people like mistakes because are weird. A mistake is always stupid and against the data though. — Preceding unsigned comment added by 2A02:587:4103:AE00:D47:B687:8172:7D1E ( talk) 23:13, 1 July 2016 (UTC)
How about a section exploring the possible solutions if we relax the Copernican Principle? — Preceding unsigned comment added by 157.14.234.194 ( talk) 11:11, 6 April 2019 (UTC)
Just read some old comments about the status of the article and so on. No offense, but if one isn't sure whether Omega is constant in time (in general, it is not), should one even attempt writing such an article?
This is an important problem (or lack of a problem, since current research suggests that it is based on a misunderstanding), but even most people who work broadly within the field of cosmology don't understand it, much less astrophysicists in general, much less scientists in general, much less the general public. — Preceding unsigned comment added by 193.29.81.233 ( talk) 11:40, 17 March 2020 (UTC)
What I don't understand at this flatness problem is that on one hand the universe seems to be flat today. Most cosmologist would indeed prefer this case. But if it is really flat it must have been so since the big bang because in this case omega needs to be the exact integer 1 and thereby would never deviate from that number (zero deviation from 1 cannot be inflated). If, for instance, the universe was spherically closed since the beginning, the observable universe also tends to increasingly getting flat like the limited surface on an inflating balloon. In that case omega only gets close to 1 but always deviates from 1 by some error. So what's the problem? Is it considered that it is highly improbable that nature started with an exact integer for omega? Is that the problem? Please explain! EternalAsker ( talk) 18:31, 20 July 2023 (UTC)