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this post was submitted on 09 Jun 2025
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Yes that's my understanding as well. Although expansion is accelerating, so maybe some time very far in the future, expansion will in fact happen faster than the forces can compensate, and the universe will just be a very, very thin cloud of subatomic particles that can't find another to form an atom with.
I may be off the deep end here, but I seem to remember reading that the acceleration can be explained by the fact that more space is created due to the expansion.
As an example: If space is expanding at 0.1 s^-1^, and we have 1 m^3^ of space, then the initial expansion rate is 0.1 m^3^s^-1^, after 1 s we have 1.1 m^3^ of space, which is expanding at 0.11 m^3^s^-1^, etc.
To reiterate: This is something I seem to remember reading some time, I'm not sure. However, if it's correct, it would mean that the acceleration is happening between bits of matter that are moving apart, not within bits of matter that are already held together. In that case, the acceleration will never be able to pull apart matter. Please correct if I've gotten this wrong, as mentioned I'm not an astrophysicist.
Huh, that makes sense. (Though per H. L. Mencken, "For every complex problem there is an answer that is clear, simple, and wrong.")
But space is between the nucleus and electrons too. There's no difference between the space between atoms and the space between subatomic particles.
Absolutely, there is space between the electrons and nucleus (insomuch as the position of both is well defined). However, what I'm suggesting is that as long as there is an electromagnetic force holding the two together, such that there is a constant (time-averaged) distance between them, that space is not expanding at an accelerating rate. At least that's my understanding of it.
Why would space there not be expanding like space everywhere else?
It is, but if the rate of expansion is constant (e.g. 0.1 m m^-1^s^-1^), then the acceleration in the speed of expansion that we observe is a result of the distance increasing.
So the space between two things that are 1 m apart will be expanding at 0.1 m s^-1^, while the space between two things that are 5 m apart will be expanding at 0.5 m s^-1^. As long as the force acting between two things is large enough to overcome the expansion rate right now, the distance between them will remain constant, because the acceleration is not a local effect but a result of the distance increasing.
As far as I understand, this is why we see other galaxies accelerating away from us, but don't see any individual galaxy "ballooning". Because locally (on the scale of a galaxy), gravitational forces overcome the rate of expansion. On large scales (to distant galaxies), there is effectively no gravitational pull, so the distance increases due to the expansion. When the distance increases, so does the observed speed of expansion, etc.
To reiterate: I'm in no way sure about this, it's just my coarse understanding of our current explanation for what we observe.