this post was submitted on 29 Sep 2024
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Not thinking of cosmic expansion as a volume expanding is an interesting thought.
It does imply that the changing distance only happens at large distances though. "Faster-than-light" expansion is already non-local (I think), but all expansion being non-local is consistent with it being driven by vacuum energy. That kinda makes the rasin bread analogy stronger, as the rasins don't expand at all.
I wonder if we could detect frame-dragging at large distances. If expansion causes frame-dragging, then it's actually a change in space, not just distance.
I wonder if linear motion can even cause frame-dragging, or if it's just rotation that causes it. I do not know enough about the math to say.
So it does happen on a small local scale though. It happens on ALL scales.
But everything is expanding from everything. Meaning the observer is always centred of the expansion. This is because volume is constant. The rasins themselves do expand, but locally it's such a small scale (10^-23 m/s for our solar system).
This also works for how we understand the change in density. Volume is constant, but we've gone from infinitely dense to almost nothing.
We went over this, we observe the distance between galaxies increasing, but the distance between atoms has not.
The expansion happens everywhere, but subatomic forces massively overpower the expansion, so atoms don't expand.
Likewise, raisins are strong enough to not get pulled apart by the expanding bread. There may be slight force on them, but the bread expanding by a factor of 2 leaves the raisins the same size.
I don't understand how you think a change in distance can be detectable by light between galaxies, but not detectable by like between ends of a metre bar, or between electrons.
You are correct that the raisins would have other constraints to keep it from infitatly expanding into nothing. Not because it's not expanding but because it has external constraints like gravity keeping it there.
They do have expansion applied to them, but gravity and other things effecting space time would be keeping it on place.
As for attoms, I think you picture something solid. But there's not. The electrons are getting further from the nucleas, but it's still bound quantum mechanically to the attoms regardless of its position.
But then the nucleas isn't soldi either. It's made of smaller things yet, and so on and so forth. So inside would also be expanding. But again other forces at play would bind things together.
The expansion is also not a force. It can't overcome other forces so it keeps things in line.
Yes, atoms are made of smaller parts; electron orbitals change chemistry based on their distance from the nucleus, nucleons change the chances of emitting radiation based on their distance from each other, and quarks greating increase their mutual attraction based on distance.
The relative distance between fundamental particles is governed primarily by forces which don't seem to have changed much since nucleosynthesis. If expansion doesn't affect any of this, then saying things governed by forces are expanding is nonsensical.
I can see a perspective where time is slowing down, reducing the effective range of the forces and letting all matter shrink to fit the changing effective distance, and leaving unbound matter to appear to expand. However, I can't see how this would be meaningfully different from an expansion of all space, not how such a difference might be detected.
Regardless, the distances within atoms continue to behave consistently, while the distances within galactic superclusters do not.