Is the Universe Really Expanding or Just Revolving Around a Central Gravity?

[Mike2]

Hi J T! Welcome to these Forums.

I'm not sure what you mean by the "initial "Big Bang" force". Forces are internal to the spatially expanding space-time manifold. This manifold is curved by the presence of the matter-energy within it and that curvature results in space-like foliations 'within it' expanding with time, also 'within it'.

However, you might want to relate cosmic acceleration with the postulated inflationary period when such acceleration was much greater. It could be caused by a false vacuum energy left over from that period.

Garth

What do they mean "false" vacuum? The vacuum is neither true nor false. Do they mean unstable vacuum?

 

[Garth]

What do they mean "false" vacuum?

Good question! It may be just an 'epicycle' to 'save the appearances, but see: False Vacuum.

Garth

 

[Mike2]

Good question! It may be just an 'epicycle' to 'save the appearances, but see: False Vacuum.

Garth

I read somewhere that QFT in curved spacetime does not allow particle creation, that only fields are considered. Could it be that during inflation space was too curved to allow particles to be pulled out of the vacuum. And so there was no matter to prevent spacetime from expanding very rapidly during inflation. But after space flattened out enough, it became possible for the particles of QFT to be pulled out of the vacuum and slow the rate of expansion. Does this sound like a possibility? Thanks.

 

[Harry Costas]

Hello All

If you work with the BBT than the universe originated from one nothing point and expanding into space. Saying that beyond the known universe there is nothing.

For one thing, the universe is endless and when we look into deep field images we see existing galaxing billions of years old. The expanding of the universe is another point. How can an infinite universe expand. The parts withing may contract and expand as we actually observe them.

If the universe is expanding can someone tell me which part.
Our local galaxy is not expanding.
Our local cluster of galaxies is not expanding
Our local cluster of cluster galaxy is not expanding.
Our super cluster of galaxies is not expanding .
see link http://astro.uwaterloo.ca/~mjhudson/research/threed/

So can someone tell me what is expanding?

 

[Jorrie]

Hello All
If you work with the BBT than the universe originated from one nothing point and expanding into space. Saying that beyond the known universe there is nothing.

No Harry, the BB theory does not say the universe originated from ‘one nothing point and expanding into space’! It says that the universe was initially infinitely (or very near infinitely) dense and space started to expand (the BB), making the density less extreme.

My take on your final question: on large scales, we observe that space is (or was) expanding. On smaller scales (even supercluster scale) it is thought that the mutual gravity overwhelms the expansion, which is small over shorter distances. But add enough teeny-weeny bits of expanding space up over the large scales and the expansion 'overwhelms' gravity.

You haven’t asked, but why does space expand?... that's a long story...

 

[marcus]

No Harry, the BB theory does not say the universe originated from ‘one nothing point and expanding into space’! It says that the universe was initially infinitely (or very near infinitely) dense and space started to expand (the BB), making the density less extreme.
.

I agree with Jorrie. Henry also asks "what is it that expands" and I think that DISTANCES expand.

In the best theory of geometry we have, it is naturally for large-scale distances to vary. they can be mostly all expanding, or in principle could be mostly all contracting (but we don't observe that happening) and it can also be a mix depending on how matter is distributed and suchlike conditions.

small scale distances can also vary but ordinarily it is so slight that it is not detectable. brief variations in distance is what gravity waves are all about!

Anyway, I think the secret is to get away from this expectation that distances should be fixed and rigid and unchanging. It simply is not true. We should not expect it.

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it can sound a bit mysterious to say "space expands" (although that is a fine way to think of it) because then people get the idea that space has to be something, like some material, and they say "what is space" and "how does it expand"----and they sometimes get confused.
So if you don't like that you can just observe that distances expand. It is just a fact of nature. No reason to expect them not to vary. Belief in Euclidean metric is prejudice.