I got this bizarre idea in my mind, after reading SCP-3321

There, as a person gets teleported through a wormhole, ends up at the edge of the Observable Universe, 46 billion light-years away from Earth. After that, he perceives a dense nebula, that gradually changes colour. From yellow to a reddish colour. It is supposedly dense, and looks sort of like this:enter image description here

According to the article, the dense nebula becomes red, as the expansion of space-time causes a massive redshift, which causes it to turn red. This effect is magnified by the fact that the nebula is extremely near the edge of the universe. The expansion of space-time too, causes the rocket to move away at really high speeds, and sooner or later, the rocket crashes into the edge of the universe, which supposedly isn't described in the article.

Wait a minute. I think I see something. It looks like this red foam just cuts off, and there's something on the other side. It looks kind of like… it looks like… oh my God-

However, this information is not going to be a actual part of the question, as the information above merely suggests where I got this idea from. The article simply poked my curiosity for space.

However, now let us move onto the "hard-sciencish" part...

On Earth, we simply cannot perceive the redshift of objects on a local scale, as space-time here expands ridiculously slowly. It simply cannot be observed on a local scale. It would be like trying to see a rock move. Space-time here is relatively stationary on a local scale.

Only at several million light years away from us, does the space-time expansion picks up pace and causes motion. And even then, we can see the redshift on a astronomical scale, not on a local scale. Galaxies and stuff are really far away and thus redshift faster. Ending up with something like this:

enter image description here

Looks cool, but this thing is happening at many million light-years away, so it is perceivable. This redshift works only on astronomical scales.

Now, let us move onto the actual question:

Let us say, an observer is stationed at 46 billion light-years away from Earth. Note that this observer is not outside the observable universe, it is still inside the observable universe, but just very, very close to the edge of it.

Now, not only are we just a few million light-years away from Earth, but several billion light-years away. This is simply where the expansion of space is theorized to be faster than the speed of light, strong enough to perhaps affect objects not only on astronomical scale, but at the local scale as well.

The question is:

Would this observer perceive the expansion of space-time on a local-scale

  • 2
    $\begingroup$ Are you also moving back in time 13.8 billion years? We see the edge of the observable universe as it was 13.8 billion years ago $\endgroup$
    – James K
    Nov 8, 2022 at 7:26
  • 4
    $\begingroup$ @Furious Arcturus "Let us say, an observer is stationed at 46 billion light-years away from Earth. Note that this observer is not outside the observable universe, it is still inside the observable universe, but just very, very close to the edge of it." You seem to be thinking there is a well-defined edge of "the" observable universe, but that's not how it works. However far away the observer goes, they are always at the center of their own observable universe. We are currently at the edge of some other possible observer's observable universe. $\endgroup$
    – D. Halsey
    Nov 8, 2022 at 11:35

1 Answer 1


If you move to a position 46 billion light years away, the universe probably looks almost exactly the same as it does here (at least on large scales).

The only reason I add "probably", is because the universe beyond 46 billion light years is unobservable and so we cannot be sure. However, we do know that the observable universe appears to be very isotropic and homogeneous on large scales and has a very small curvature (consistent with being flat), that suggests the actual universe is way bigger than what we can actually observe.

There is no theory that suggests the spacetime 46 billion light years away is any different to that here. On the contrary, in the predominant theoretical models it is presumed to be identical at the same cosmic epoch; everywhere in the universe would agree that the universal expansion is occurring in the same way. This is known as the "cosmological principle" - the universe looks the same wherever you are (though not whenever, see below).

If I were to interpret your question to move to the edge of the observable universe, as it was when the light was emitted (roughly 13.7 billion years ago) then the answer is a little different. You would be sitting in a hot (3000 K) plasma, surrounded by a fog of orange/red light coming from all directions equally. There would be no stars or galaxies in existence. This is the plasma responsible for emitting the cosmic microwave background; the redshifted remnants of which we see today. It is this "fog" that defines the edge of the observable universe (for electromagnetic radiation).


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