I assume there is some limit to how far our telescopes could actually see, and that this distance would be about the same in all directions. So, as a layman, I would assume that an infinite universe would appear spherical, with the telescope appearing to be at the center.

Is this assumption incorrect, and if so, what would an infinite universe look like through a large telescope such as James Webb?

edit: also assume the universe is infinite AND filled with matter similar to what we see locally (galaxys,filaments,etc)

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    $\begingroup$ See en.wikipedia.org/wiki/Observable_universe $\endgroup$ Aug 10, 2023 at 17:02
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    $\begingroup$ At first, I was going to ask how on earth you came to the conclusion that the infinite universe would be spherical. And then I realised the clever complexity of your question. $\endgroup$ Aug 10, 2023 at 20:59
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    $\begingroup$ possibly no different than it does now $\endgroup$
    – uhoh
    Aug 11, 2023 at 4:15
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    $\begingroup$ Your question sounds like a telescope is something that "throws a look at a direction and has a limit", it's the other way round, you should think about it as all the universe around throwing rays and we only see those that reach the telescope. So that the limit is not a sphere, it depends on the speed of the rays, what they went through etc. As the guy said "All is relative". You can even have the same image from different times repeated at different locations because of distortions made by black holes $\endgroup$
    – Kaddath
    Aug 11, 2023 at 9:31
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    $\begingroup$ Your question relates to Olbers paradox $\endgroup$
    – Fattie
    Aug 11, 2023 at 14:28

1 Answer 1


If the universe were infinite in space, but finite in time, we could see back no further than a light-travel time of the age of the universe. — This is very possibly reality. We can see back to times shortly after the big bang. In principle, we could see right back to the big bang, but in practice, this isn't possible since the early universe was opaque. So the real answer is we can and do see what an infinite-in-space universe looks like, because that is what our universe looks like.

If the universe were infinite in space and in time and pretty much static and homogenous, then Olbers' paradox applies: every line of sight ends in a star and the sky burns at thousands of degrees. This isn't the universe as we observe it.

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    $\begingroup$ Strictly speaking, we don't (and can't) know whether our universe is infinite. All we can say is that it's at least as big as the observable universe that you describe here. We don't really know whether the universe is finite in time, either - only that our little corner can be traced back as far as the Big Bang and no further. $\endgroup$ Aug 11, 2023 at 13:48
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    $\begingroup$ @toby Right, but, if the universe was infinte in space, but finite in time, it would look exactly like the universe does look to us. There is another question "What would the universe look like if it was finite" And "What would the universe look like if it were finite, but much smaller than the observable universe (would we see multiple images of the galaxies, from light that has gone "all the way round") $\endgroup$
    – James K
    Aug 11, 2023 at 13:53
  • $\begingroup$ I was just taking exception to the claim, "because that is our universe." I'd say "citation needed". I agree on everything else, and you have my upvote. :-) $\endgroup$ Aug 11, 2023 at 14:03
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    $\begingroup$ I've modifed that line. Our universe looks like a universe that is infinite in extent, even if it actually isn't. $\endgroup$
    – James K
    Aug 11, 2023 at 14:37
  • $\begingroup$ @TobySpeight In practical terms, if it were possible to decide conclusively whether the Universe were finite or infinite simply by looking at it with a telescope we'd have done so long ago. $\endgroup$ Aug 11, 2023 at 22:17

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