Talk:Cosmological Principle

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[edit] Support for this

What observations and axioms support this. Hackwrench 18:08, 1 November 2005 (UTC)

My understanding, and perhaps someone can correct/expand as needed, is that the cosmological principle is itself taken as an axiom, but there is experimental evidence as well. The best evidence for isotropy is the [cmb] which is isotropic to one part in 10,000. I think for homogeneity, we can look at other galaxies/clusters and see that the physics there appears to be the same, and galaxies on average are the same. Threepounds 06:54, 26 November 2005 (UTC)

[edit] This vs. Anthropic

OK, I'll bite: Under what logic does the Cosmological principle disprove the Anthropic principle? Do sources exist for such claims? ----Jasonuhl 21:26, 13 October 2005 (UTC)

I agree that this needs to be expanded. I think more needs to be said or this part removed. It seems to be that the Cosmological principle is a statement about averages over cosmological distances (as the article indicates) while humanity exists on an entirely negligible length-scale. It is not obvious to me how the two should be compared or where a contradiction exists. Threepounds 06:42, 26 November 2005 (UTC)

I've removed this sentence. The link between this and the Anthropic principle seems tenuous at best, and a claim that one disproves the other without any attempt at explanation adds nothing but confusion. ----Jasonuhl 23:42, 21 February 2006 (UTC)

[edit] Milne's Formalization of the Cosmological Principle

I found a link in Timeline of cosmology that said Milne "formalized" this cosmological principle. While I agree that he did, I don't think that the gist of his argument is well presented here. For instance, Milne did not like the idea of a finite universe, nor did he like the idea of expanding space.

Milne says in Relativity, Gravitation, and World Structure "I am well aware that some mathematicians believe that such difficulties are at once swept awy if we use the concept of 'curved space.' I have examined such attempts at explanation with the greatest care, and I have found that in all cases the proposed explanations break down at some point. Two-dimensional analogies with hypothetical inhabitants on the surface of a sphere fail as soon as we recall that a survey of the astronomical universe is made by taking a photograph with a telescope and camera, and that, for a telescope of arbitrarily large light-gathering power, either the number of nebulae that can be counted is finite and therefore contains one faintest and so presumably most distant member, or it is infinite, in which case either the same nebula is photographed as an infinite number of separate spots or the total number of actual nebulae in existence is infinite. The latter will be our eventual conclusion. Here I am only concerned to argue that the phrase 'curvature of space' used in connexion with astronomical photographs merely involves a mist of mysticism. Such photographs can always be interpreted in flat space, and then the assumption of a finite number of density-maxima inevitably leads to some kind of accessible edge of the universe."

In this book, at least, Milne eventually concluded that the universe was not finite in terms of number of nebulae. He did not conclude that space was curved. JDoolin 16:27, 27 August 2006 (UTC)