<p>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.</p>
<p>If the universe were infinite in space and in time and pretty much static and homogenous, then <a href="https://en.wikipedia.org/wiki/Olbers%27_paradox" rel="nofollow noreferrer">Olbers' paradox</a> 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.</p>

CC BY-SA 4.0
2023-08-11T13:48:21.203Z
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.
Toby Speight
CC BY-SA 4.0
2023-08-11T13:53:00.643Z
@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")
James K
CC BY-SA 4.0
2023-08-11T14:03:29.667Z
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.  :-)
Toby Speight
CC BY-SA 4.0
2023-08-11T14:37:52.387Z
I've modifed that line.  Our universe looks like a universe that is infinite in extent, even if it actually isn't.
James K
CC BY-SA 4.0
2023-08-11T22:17:55.237Z
@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.
Mark Morgan Lloyd
CC BY-SA 4.0
2023-08-10T21:29:23.777Z
2023-08-12T10:35:09.243Z
2023-08-12T10:35:09.243Z
James K
<p>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.</p>
<p>Is this assumption incorrect, and if so, what would an infinite universe look like through a large telescope such as James Webb?</p>
<p>edit: also assume the universe is infinite AND filled with matter similar to what we see locally (galaxys,filaments,etc)</p>

CC BY-SA 4.0
2023-08-10T17:02:08.857Z
See https://en.wikipedia.org/wiki/Observable_universe
Nuclear Hoagie
CC BY-SA 4.0
2023-08-10T20:59:29.943Z
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.
White Prime
CC BY-SA 4.0
2023-08-11T04:15:26.437Z
possibly no different than it does now
uhoh
CC BY-SA 4.0
2023-08-11T09:31:41.990Z
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
Kaddath
CC BY-SA 4.0
2023-08-11T14:28:42.890Z
Your question relates to **Olbers paradox**
Fattie
CC BY-SA 4.0
2023-08-12T00:08:43.747Z
You are correct about there being a limit in all directions, but it is not a distance limit. It is a limit in time. The farther we look, the further into the past we look.  The farthest we can see is basically back to the Big Bang. More precisely, we can't see beyond that because in all directions there's an obstruction – the leftover echo of the fiery plasma that once existed everywhere.
RC_23
CC BY-SA 4.0
2023-08-12T00:24:19.257Z
About the same as it does right now.
Hearth
CC BY-SA 4.0
2023-08-12T16:53:28.597Z
The Hubble looked at a dark patch of sky for a month and made the Deep Field. It looked like the intro to the original *Cosmos*. Then JWST looked at it so well that it saw basically red and blue TV static. Past that is the edge of the light cone, so that's about it.
Mazura
<telescope><universe>
If the universe were infinite, how would it look through a telescope?
hermancain
# If the universe were infinite, how would it look through a telescope?

(Asked by: username_0 on 2023-08-10)

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 username_9 Webb?

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

**Tags:** telescope, universe

> **Comments:**
> **username_1**: See https://en.wikipedia.org/wiki/Observable_universe  
> **username_2**: 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.  
> **username_3**: possibly no different than it does now  
> **username_4**: 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  
> **username_5**: Your question relates to **Olbers paradox**  
> **username_6**: You are correct about there being a limit in all directions, but it is not a distance limit. It is a limit in time. The farther we look, the further into the past we look.  The farthest we can see is basically back to the Big Bang. More precisely, we can't see beyond that because in all directions there's an obstruction – the leftover echo of the fiery plasma that once existed everywhere.  
> **username_7**: About the same as it does right now.  
> **username_8**: The Hubble looked at a dark patch of sky for a month and made the Deep Field. It looked like the intro to the original *Cosmos*. Then JWST looked at it so well that it saw basically red and blue TV static. Past that is the edge of the light cone, so that's about it.  

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## 1 answers

### Answer by username_9 on 2023-08-10. Score: 21 | Accepted answer

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](https://en.wikipedia.org/wiki/Olbers%27_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.

> **Comments:**
> **username_10**: 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.  
> **username_9**: @username_10 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")  
> **username_10**: 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.  :-)  
> **username_9**: I've modifed that line.  Our universe looks like a universe that is infinite in extent, even if it actually isn't.  
> **username_11**: @username_10 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.  

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