Talk:Observable universe

What is the topic here?

As far as I am concerned this article is about the cosmological term "observable universe". However a bunch of the later material here is "things that can be observed in the universe", which as far as I can tell should all be in Universe. Am I right? Johnjbarton (talk) 19:32, 27 September 2025 (UTC)

I propose to move or remove two sections of the article over in Talk:Universe#Proposal_to_move_content_from_Observable_universe Johnjbarton (talk) 23:20, 16 December 2025 (UTC)

As I noted in Talk:Universe, I think we should rather separate large-scale structure into its own article. Aseyhe (talk) 00:32, 17 December 2025 (UTC)

FAQ

After I added a G3 speedy deletion for Draft:93B LY's circumference not diameter. questioning the quoted diameter of 93 Gly, I think we need an FAQ about the correct size of the observable universe. –LaundryPizza03 (dc̄) 05:12, 23 December 2025 (UTC)

I put the radius in the second sentence. To be honest, nothing we write will prevent the occasional wacky draft. Johnjbarton (talk) 16:25, 23 December 2025 (UTC)

"Soapbubble superstructure of galactic walls" listed at Redirects for discussion

The redirect Soapbubble superstructure of galactic walls has been listed at redirects for discussion to determine whether its use and function meets the redirect guidelines. Readers of this page are welcome to comment on this redirect at Wikipedia:Redirects for discussion/Log/2025 December 20 § Soapbubble superstructure of galactic walls until a consensus is reached. Jay 💬 05:01, 28 December 2025 (UTC)

Exotic, disputed, highly technical claims for the size of the universe are off topic.

The section "The universe" versus "the observable universe" has grown cruft in the form of discussions of highly technical and not clearly encyclopedic estimates of non-observable size of the universe. In my opinion this material is off topic. The topic here is the "observable universe" and an explanation of difference is fine, but not on and on with exotic estimates. Note that these sources are not even primarily about the size of the universe, so they are being stretched to even be off topic. One way to tell that these sources are not related to this topic is to look at the papers that cite them. None of those papers are about the size of the universe, observable or otherwise. Johnjbarton (talk) 03:40, 10 August 2026 (UTC)

Agreed. Go ahead and trim it down a lot! - Parejkoj (talk) 15:09, 12 August 2026 (UTC)

I moved the content to Size of the universe, unedited. The resulting section still needs work. Johnjbarton (talk) 21:14, 14 August 2026 (UTC)

Boundary

The problem with the word "boundary" in the context of the recent edits is that it seems to be meant as saying that a spacelike slice of the universe doesn't look like, say, the closed 3-ball, which is fine but it's only part of the point. It doesn't exclude, for example, the open 3-ball (not embedded in anything); that also has no boundary.

The idea that really needs to be expressed here is that you can go unboundedly far in a "straight line" in any direction. In the open 3-ball you couldn't do that; there would be some point at which you couldn't keep going another mile in the same direction. Mathematically this is saying that the universe is a geodesic manifold. This might be a good point to put in an explanatory footnote.

(It's true that I don't immediately know where to find a source. I have O'Neill's textbook and actually took differential geometry from him personally, but I don't know whether he treated this particular point, and unfortunately physicists tend to be infuriatingly blasé about expressing their ideas in correct mathematical language.) --Trovatore (talk) 18:11, 14 August 2026 (UTC)

Yeah, it should definitely remain "finite but unbounded" which is standard usage in cosmology. Wrt sources, this should provide a starting point:

Find sources: Google (books · news · scholar · free images · WP refs) · FENS · JSTOR · TWL

We don't adjudicate what is "correct" (which amounts to WP:OR in this case), but rather what is sourced. Thanks, Mathglot (talk)

There really ought to be some sort of note that "unbounded" here does not mean the same thing as in mathematics. I'll see if I can find some sourced discussion. --Trovatore (talk) 18:11, 17 August 2026 (UTC)