Talk:De Sitter universe

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This Doesn't Make Sense to Me[edit]

"Acceleration becomes faster than light" is apples and oranges to me. FelisSchrödingeris (talk) 06:50, 15 January 2008 (UTC)[reply]

I changed it to "Relative Expansion becomes faster than light" because light does not accelerate. It always travels at the speed of light by definition and speed and acceleration are different things. —Preceding unsigned comment added by 86.153.60.15 (talk) 19:15, 25 December 2008 (UTC)[reply]

This is still incorrect, galaxies at a redshift greater than 1.641 were "moving" faster than light when the light we see was emitted. The section needs a rewrite. I'll attempt that later if I have time. George Dishman (talk) 08:18, 12 January 2014 (UTC)[reply]

Question[edit]

Should this sentence

If our universe is approaching a de Sitter universe then eventually we will not be able to observe any galaxies other than our own Milky Way

instead read ...

If our universe is approaching a de Sitter universe then eventually we will not be able to observe any galaxies beyond the Local (Virgo) Supercluster

?. Isn't our supercluster being held together by the Great Attractor?
Also I think these should be kept separate articles. The De Sitter space article is all math
Regards,
70.27.103.81 03:29, 6 October 2005 (UTC)[reply]

I'm not sure the Virgo Supercluster is a bound system gravitationally, as the text of that article suggests that all galaxies in it are receding from each other due to Hubble expansion. The Local Group is bound, if I recall correctly. --Christopher Thomas 00:19, 9 January 2006 (UTC)[reply]

Merge proposal[edit]

Keep them separate. The De Sitter space article is the pure mathematical description of it, uncluttered by cosmological topics. Those cosmological aspects are better discussed it a separate article. It is sufficient for the two to mutually link each other.

panini —The preceding unsigned comment was added by 71.139.109.107 (talk • contribs) on 10:04, 11 November 2005.

I agree that the two articles should remain seperate, for the obvious reason that they are not covering the same topic. The math of the De Sitter space article is supplementary to the cosmological explanations of the De Sitter universe article. Can we somehow remove the banner suggesting the merger, it can confuse and distract people. - Mephistophyles 23:05, 24 December 2005 (UTC)[reply]

de Sitter horizon[edit]

Should this term perhaps be discussed in this article? (See) __meco (talk) 13:52, 30 March 2009 (UTC)[reply]

Planck Mass, CC and Hubble Parameter[edit]

To see how the Planck mass does not enter in the relation of cosmological constant to Hubble parameter take the trace of the vacuum Einsteins equation:

-R+4k\Lambda =0\Rightarrow R=12H^{2}=4k\Lambda

where R is the scalar curvature and k is a constant which is largely a matter of taste and is usually chosen either 1 or 1/2. The first equality in the right formula follows from a straight forward calculation of the scalar curvature of a DeSitter metric. However a reference to the planck mass enters, if you want to relate the cosmological constant to some kind of ("dark") energy, because this means interpreting the cosmological constant term as energy-momentum tensor, where a multiplication with the square of the planck mass ist needed to compensate for the $8\pi G$ prefactor of the energy-momentum tensor. Cheers -- 194.95.184.126 (talk) 14:17, 23 March 2010 (UTC)[reply]