Talk:Particle horizon

From Wikipedia, the free encyclopedia

	This article is within the scope of WikiProject Physics, which collaborates on articles related to physics.	Physics Portal
Stub	This article has been rated as Stub-Class on the assessment scale.
???	This article has not yet received an importance rating within physics.
Help with this template This article has been rated but has no comments. If appropriate, please review the article and leave comments here to identify the strengths and weaknesses of the article and what work it will need.

This article has been automatically assessed as Stub-Class by WikiProject Physics because it uses a stub template. If you agree with the assessment, please remove {{Physics}}'s auto=yes parameter from this talk page. If you disagree with the assessment, please change it by editing the class parameter of the {{Physics}} template, removing {{Physics}}'s auto=yes parameter from this talk page, and removing the stub template from the article.

[edit] Merge With Observable Universe

It should be merged with the above article because it adds nothing that cannot otherwise be explained in a one or two sentence statement in that article as it is done here. And in fact, it is more contextually appropriate in that article as well. Anyone have any objections to merging it? Astrobayes 20:41, 23 June 2006 (UTC)

Hi, IMHO this should stay a separate article. For one, you can define a particle horizon even for universes that are not ours (eg, for general spacetime metrics), so it's not necessarily related only to our universe, but really to any spacetime you like. Also, I imagine that "observable universe" should really refer to properties of the universe as observed.

That being said, however, taking a peek at the "observable universe" article it seems to be in a rather confused state at the moment. As you say it's mostly talking about the particle horizon in the context of the standard cosmological model. Perhaps what this article needs is a more general discussion of what particle horizon means in spacetimes more general than the FRW metric. Wesino 18:42, 23 November 2006 (UTC)

[edit] Major edits

I did a bit of heavy editing. There were a few factual inaccuracies (or fuzzy statements), for example

• what was defined previously was not the conformal time but the change in conformal time,
• the particle horizon is only equal to the conformal time when we're measuring it in comoving distance (otherwise there is a factor of a(t))
• conformal time doesn't describe a universe that is expanding (this is the job of the metric, which can use the c.t. as one coordinate)
• the article seemed to suggest that just because the overall scale of the universe is expanding, then there are no horizons, which is false.

Also it wasn't really clear why things had to be a list. Anyway, I hope that the edits kept the sense and intention of the original information. If you don't think so let's talk and come up with a better solution. Wesino 18:59, 23 November 2006 (UTC)