<p>The furthest we can "see" is the cosmic microwave background at a redshift of about 1100.</p>

<p>The proper distance of the CMB-emitting gas that we see today is about 46 billion light years.</p>

<p>If you are talking about galaxies, then the first are thought to have formed at redshifts of about 20 (current distance 36 billion light years) and beyond that are the universe's "dark ages" where no stars or galaxies should exist; the most distant galaxies observed at the moment are at redshifts of about 10 (current distance 31 billion light years).</p>

<ul>
<li>All current distances depend on the adopted cosmological model. The numbers are for a flat <span class="math-container">$\Lambda$</span>CDM universe with the Planck cosmological parameters.</li>
</ul>

<p>There is no chance of seeing our own Galaxy, since it only formed about 12 billion years ago and the universe is a lot bigger than 12 billion light years.</p>

CC BY-SA 4.0
2019-06-12T20:21:03.043Z
I was thinking more in terms of galaxies rather than gases,but in particular I wanted to know how far would it be until the best instruments & telescopes available in the foreseeable future could detect nothing at all. Already the farthest galaxies are becoming small & faint.
Michael Walsby
CC BY-SA 4.0
2019-06-13T01:25:36.453Z
This is a thought provoking answer! However I'm not sure if said provoked thoughts I'm having are correct. So I've just asked [Is the CMB's "surface of last scattering" 46 billion light-years away?](https://astronomy.stackexchange.com/q/32270/7982)
uhoh
CC BY-SA 4.0
2019-06-12T18:54:11.047Z
2019-06-13T06:23:40.677Z
2019-06-13T06:23:40.677Z
ProfRob
<p>Radius of the observable universe is 47.5 billion light years,which means we are seeing things which are about 48 billion light years away. At a rough estimate,at what distance would our finest instruments and telescopes be unable to see or detect anything at all,&amp; is there anything in the idea that if we were able to see far enough,we might see our own galaxy as it appears from an immense distance,its light having circled the universe? And as space is not a perfect vacuum,wouldn't the light be significantly retarded by the end of such a long journey?</p>

CC BY-SA 4.0
2019-06-12T11:45:31.303Z
https://chat.stackexchange.com/transcript/message/50517334#50517334
PM 2Ring
CC BY-SA 4.0
2019-06-12T11:49:06.997Z
PM,I remember we tried to use the chatline about a week ago,& I found it unsatisfactory. You agreed at the time it needed rationalisation.
Michael Walsby
CC BY-SA 4.0
2019-06-12T11:59:20.940Z
I said that chat is somewhat limited. But it is still quite usable. I put that link here because in that chat I mentioned that yes, in theory a photon could "circumnavigate" the universe, *if* the universe has positive curvature, and *if* the rate of expansion were small enough, but that current measurements indicate that neither of those things are likely to be true.
PM 2Ring
CC BY-SA 4.0
2019-06-12T18:03:38.427Z
You seem to be mixing two questions.  First - can we reliably detect single photons. Second, what's the most distant object that was within our observable sphere at the time it emitted a photon?
Carl Witthoft
CC BY-SA 4.0
2019-06-12T20:25:38.437Z
No,I asked how far could we see before the most advanced instruments of the foreseeable future could detect nothing at all. Already the most distant galaxies we can see are only barely detectable.
Michael Walsby
CC BY-SA 4.0
2019-06-12T22:56:32.433Z
@MichaelWalsby suspect that you are not only asking about detection limits but also angular resolution limits (i.e. resolving small and faraway objects into sensible pictures). Maybe you want to add that part in explicitly?
Ingolifs
CC BY-SA 4.0
2019-06-13T01:59:48.707Z
We can already see the most distant light: it’s impossible to detect any EMR older (ie more distant) than the CMB. Your question would be much more interesting if you moved beyond “seeing” (ie light) and explicitly included detecting things like gravitational waves and cold neutrinos, which exist from the first minutes after the BB.
Chappo Hasn't Forgotten
CC BY-SA 4.0
2019-06-13T06:21:41.350Z
@chappo Then the answer becomes 47.5 billion light years.
ProfRob
CC BY-SA 4.0
2019-06-13T08:16:11.373Z
@RobJeffries yes, *if* we could develop the technologies to detect them. Do you think either is a realistic possibility? For example, do we need to solve quantum gravity before we can model a BB GW signature? I’d have thought low-energy neutrinos would be just about impossible to detect, but then Einstein himself thought we’d never be able to detect GWs.
Chappo Hasn't Forgotten
CC BY-SA 4.0
2019-06-13T17:06:54.163Z
There seems to be an assumption that gravitons exist & gravity can be quantised,but maybe there are no gravitons (or anti-gravitons),& gravity can't be quantised. If a graviton set out from Earth & hit a proton 2.5m light years away in the Andromeda galaxy,I'd say that was bloody good shooting,wouldn't you? Almost unbelievably good.
Michael Walsby
CC BY-SA 4.0
2022-07-24T13:43:47.683Z
related and with potentially helpful answers [Is there anything currently 46 billion light years away from Earth that we can see?](https://astronomy.stackexchange.com/q/50011/7982)
uhoh
<radio-astronomy><observable-universe><cosmic-microwave-background>
What Is The Maximum Distance Our Finest Instruments Could See When They're Perfected?
Michael Walsby
# What Is The Maximum Distance Our Finest Instruments Could See When They're Perfected?

(Asked by: username_0 on 2019-06-12)

Radius of the observable universe is 47.5 billion light years,which means we are seeing things which are about 48 billion light years away. At a rough estimate,at what distance would our finest instruments and telescopes be unable to see or detect anything at all,& is there anything in the idea that if we were able to see far enough,we might see our own galaxy as it appears from an immense distance,its light having circled the universe? And as space is not a perfect vacuum,wouldn't the light be significantly retarded by the end of such a long journey?

**Tags:** radio-astronomy, observable-universe, cosmic-microwave-background

> **Comments:**
> **username_1**: https://chat.stackexchange.com/transcript/message/50517334#50517334  
> **username_0**: PM,I remember we tried to use the chatline about a week ago,& I found it unsatisfactory. You agreed at the time it needed rationalisation.  
> **username_1**: I said that chat is somewhat limited. But it is still quite usable. I put that link here because in that chat I mentioned that yes, in theory a photon could "circumnavigate" the universe, *if* the universe has positive curvature, and *if* the rate of expansion were small enough, but that current measurements indicate that neither of those things are likely to be true.  
> **username_2**: You seem to be mixing two questions.  First - can we reliably detect single photons. Second, what's the most distant object that was within our observable sphere at the time it emitted a photon?  
> **username_0**: No,I asked how far could we see before the most advanced instruments of the foreseeable future could detect nothing at all. Already the most distant galaxies we can see are only barely detectable.  
> **username_3**: @MichaelWalsby suspect that you are not only asking about detection limits but also angular resolution limits (i.e. resolving small and faraway objects into sensible pictures). Maybe you want to add that part in explicitly?  
> **username_4**: We can already see the most distant light: it’s impossible to detect any EMR older (ie more distant) than the CMB. Your question would be much more interesting if you moved beyond “seeing” (ie light) and explicitly included detecting things like gravitational waves and cold neutrinos, which exist from the first minutes after the BB.  
> **username_5**: @chappo Then the answer becomes 47.5 billion light years.  
> **username_4**: @RobJeffries yes, *if* we could develop the technologies to detect them. Do you think either is a realistic possibility? For example, do we need to solve quantum gravity before we can model a BB GW signature? I’d have thought low-energy neutrinos would be just about impossible to detect, but then Einstein himself thought we’d never be able to detect GWs.  
> **username_0**: There seems to be an assumption that gravitons exist & gravity can be quantised,but maybe there are no gravitons (or anti-gravitons),& gravity can't be quantised. If a graviton set out from Earth & hit a proton 2.5m light years away in the Andromeda galaxy,I'd say that was bloody good shooting,wouldn't you? Almost unbelievably good.  
> **username_6**: related and with potentially helpful answers [Is there anything currently 46 billion light years away from Earth that we can see?](https://astronomy.stackexchange.com/q/50011/7982)  

---

## 1 answers

### Answer by username_5 on 2019-06-12. Score: 5

The furthest we can "see" is the cosmic microwave background at a redshift of about 1100.

The proper distance of the CMB-emitting gas that we see today is about 46 billion light years.

If you are talking about galaxies, then the first are thought to have formed at redshifts of about 20 (current distance 36 billion light years) and beyond that are the universe's "dark ages" where no stars or galaxies should exist; the most distant galaxies observed at the moment are at redshifts of about 10 (current distance 31 billion light years).

* All current distances depend on the adopted cosmological model. The numbers are for a flat $\Lambda$CDM universe with the Planck cosmological parameters.

There is no chance of seeing our own Galaxy, since it only formed about 12 billion years ago and the universe is a lot bigger than 12 billion light years.

> **Comments:**
> **username_0**: I was thinking more in terms of galaxies rather than gases,but in particular I wanted to know how far would it be until the best instruments & telescopes available in the foreseeable future could detect nothing at all. Already the farthest galaxies are becoming small & faint.  
> **username_6**: This is a thought provoking answer! However I'm not sure if said provoked thoughts I'm having are correct. So I've just asked [Is the CMB's "surface of last scattering" 46 billion light-years away?](https://astronomy.stackexchange.com/q/32270/7982)  

---

