<blockquote>
<blockquote>
<p>The CMB is visible at a distance of 13.8 billion light years in all directions from Earth, leading scientists to determine that this is the true age of the Universe.</p>
</blockquote>
</blockquote>
<p>This is wrong in a few ways. First, we do have good reason to think that the CMB was produced around 13.8 billion years ago, but that doesn't mean it's 13.8 billion light years away. The light is right here (that's how we detect it), and the matter that emitted the light is roughly 47 billion light years away in the present era, if our cosmological model is correct.</p>
<p>Second, we don't work out the age of the universe from the distance to the CMB (or the matter that emitted it). We can't see how far away it is. We work out the age of the universe by fitting a cosmological model to a variety of evidence (including the detailed spectrum of the CMB), and then we say that the CMB was emitted 13.8 billion years ago because that's what the model implies.</p>
<p>Third, the CMB doesn't date back to the beginning of the universe – although the time from the big bang/end of inflation to the emission of the CMB (around 380,000 years) is so much smaller than the time from the big bang to now (around 13.8 billion years) that this makes little difference.</p>
<p>We aren't at the center of the universe. The universe is just homogeneous (the same everywhere), and it's large enough that light hasn't had enough time to cross it since the CMB was emitted. The CMB we see is from the same distance in every direction because it's all been traveling for the same amount of time. So your first scenario is the correct one.</p>

CC BY-SA 4.0
2020-08-14T07:49:49.050Z
Perhaps you could clarify that OP's 1st scenario is *almost* clear and the technological aspect don't count much.
Alchimista
CC BY-SA 4.0
2023-05-05T04:20:52.827Z
What do you mean by "we"?
Bekim Bacaj
CC BY-SA 4.0
2023-05-06T04:54:46.837Z
@BekimBacaj I mean "we human beings", or something of that sort.
benrg
CC BY-SA 4.0
2020-08-12T19:34:39.157Z
2020-08-12T19:34:39.157Z
benrg
<p>I've read from different sources that:</p>
<blockquote>
<p>The CMB is visible at a distance of 13.8 billion light years in all
directions from Earth, leading scientists to determine that this is
the true age of the Universe.</p>
</blockquote>
<p>And that got me thinking, if this is true, there are 2 possible scenarios:</p>
<ul>
<li>These are not really the true limits of the universe, but it's the farthest we can watch with our actual technology.</li>
<li>Or we happen to be the center of the universe, because we see the &quot;beginning&quot; of it at the same distance no matter the direction we see at (which I think this a dumb supposition)</li>
</ul>
<p>So, why do we actually see the CMB at the same distance no matter what direction we look at?</p>

CC BY-SA 4.0
2020-08-12T19:19:44.027Z
https://astronomy.stackexchange.com/questions/27453/ Why can we still see the CMB? might help you.
James K
CC BY-SA 4.0
2023-05-05T04:33:55.107Z
13.8 was the farthest we could see until JWST.
Universe is limitless.
Bekim Bacaj
<big-bang-theory><observable-universe><cosmic-microwave-background><early-universe>
Why is the Cosmic Microwave Background at the same distance no matter the direction we look?
c4b4d4
# Why is the Cosmic Microwave Background at the same distance no matter the direction we look?

(Asked by: username_0 on 2020-08-12)

I've read from different sources that:

> The CMB is visible at a distance of 13.8 billion light years in all
> directions from Earth, leading scientists to determine that this is
> the true age of the Universe.

And that got me thinking, if this is true, there are 2 possible scenarios:

* These are not really the true limits of the universe, but it's the farthest we can watch with our actual technology.
* Or we happen to be the center of the universe, because we see the "beginning" of it at the same distance no matter the direction we see at (which I think this a dumb supposition)

So, why do we actually see the CMB at the same distance no matter what direction we look at?

**Tags:** big-bang-theory, observable-universe, cosmic-microwave-background, early-universe

> **Comments:**
> **username_1**: https://astronomy.stackexchange.com/questions/27453/ Why can we still see the CMB? might help you.  
> **username_2**: 13.8 was the farthest we could see until JWST. Universe is limitless.  

---

## 1 answers

### Answer by username_3 on 2020-08-12. Score: 5 | Accepted answer

> > The CMB is visible at a distance of 13.8 billion light years in all directions from Earth, leading scientists to determine that this is the true age of the Universe.

This is wrong in a few ways. First, we do have good reason to think that the CMB was produced around 13.8 billion years ago, but that doesn't mean it's 13.8 billion light years away. The light is right here (that's how we detect it), and the matter that emitted the light is roughly 47 billion light years away in the present era, if our cosmological model is correct.

Second, we don't work out the age of the universe from the distance to the CMB (or the matter that emitted it). We can't see how far away it is. We work out the age of the universe by fitting a cosmological model to a variety of evidence (including the detailed spectrum of the CMB), and then we say that the CMB was emitted 13.8 billion years ago because that's what the model implies.

Third, the CMB doesn't date back to the beginning of the universe – although the time from the big bang/end of inflation to the emission of the CMB (around 380,000 years) is so much smaller than the time from the big bang to now (around 13.8 billion years) that this makes little difference.

We aren't at the center of the universe. The universe is just homogeneous (the same everywhere), and it's large enough that light hasn't had enough time to cross it since the CMB was emitted. The CMB we see is from the same distance in every direction because it's all been traveling for the same amount of time. So your first scenario is the correct one.

> **Comments:**
> **username_4**: Perhaps you could clarify that OP's 1st scenario is *almost* clear and the technological aspect don't count much.  
> **username_2**: What do you mean by "we"?  
> **username_3**: @username_2 I mean "we human beings", or something of that sort.  

---

