this post was submitted on 29 Sep 2024
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The reason the speed of light doesn change is because rthe universe bends the rules of time to make it the same. So as the universe expands, the speed of light stays the same because the definition of time changes.
Like I said. The expansion of the universe isn't space expanding, it's the definition of distance that's expanding. Yes time is being fucked with as part of the expansion. But the universe doesn't hold distance or time as constant frames to compare to. As speed is only calculated with a frame of reference. Where distance is a little more fundamental to the universe.
Because the scale is so so much less. Like 73 km/s/Mpc.
So the rate of something to the scale of 10^-9m, would be somewhere in the order of 10^-25m/s. Which is much much smaller than anything with the attoms itself.
But the distance is always the same. A meter is still a meter in all points of time. But it's still bigger.
And yet you said that a metre bar would be larger yet measure the same. If all the aspects of the universe are expanding in lockstep such that any distance appears constant, then redshift caused by expansion is impossible.
If the increasing distance between atoms is unmeasurable, then so too must be the increasing distance between galaxies be undetectable.
LIGO can detect changes of distance on the order of 10⁻²¹, and it should be increasing in effective length by 2×10⁻¹²m/s, yet I don't see any mention of any large interferometer measuring anything but gravitational waves, and I don't see any large time-dependent components of LIGOs systemic error data.
We also can measure the increasing distance of galaxies via redshift, so unless you can explain how light from galaxies is different from the light in a large interferometer, I must conclude that the interferometers aren't expanding at the same rate as the observed expansion of the universe.
We aren't expanding like the universe is expanding.
We can still measure the red/blue shift to find the star, but if you don't correct for it, it will be wrong.
Also I don't know enough about gravitational waves wo know how it would be effected by the expansion of the universe.
But remember when LIGO measures, it's not measuring absolute values that we would see drift in. It's all relative measurements from a short time period prior. It would follow in lockstep with the expansion.
Also gravitational waves arent particles. They're disturbances in the fabric of the universe. So they don't behave like standard waves do. They have their own wave mechanics that I haven't studied.
And light is having its wavelength stretched. Speed of is not proportional to frequency in a vacuum only the permittivity and permeability of free space. So it's wavelength is getting expanded without
But again. Space isn't expanding. Distance is.
Also that's not how informeters work.
They compare distance across two lines. They can only detect the differences between those lines. Because expansion is universal in all directions, it's not detectable on informeters.
Actually that's a good point about interferometers, the only detectable change whould be in the difference between each arm's length.
Gravitational waves do behave like EM waves, we've seen a neutron star merger simultaneously in gravity and light. If there was a difference, one observation would lag behind.
How exactly would we measure an absolute value of distance? The whole thing about general relativity is than everything is relative. If everything was scaled up such that the fine structure constant stayed the same, we wouldn't be able to measure a difference.
Which brings us back to the question I have with your model: How can a changing distance be measured by light to be the same (metre bar) but also different (redshift)? If light is scaling with the rest of the universe, it shouldn't get shifted. This in the crux of my confusion.
The answer is there's no such thing as absolute distance. Because there's no such thing as absolute position. Quantum garuntees inaccuracies in position.
And your right. We can't actually measure the expansion of the universe directly. It's actually because of the red shift we do.
The reason we can see the red shift is because the universe holds the speed of light in a vacuum constant.
So if the universe is expanding, and the speed of light is expanding with it, in-order for the speed of light to stay the same, it has to travel more distance in a time. Meaning it's stretching it's wavelength as it moves. Just like something moving away from us does. IIRC it's because of observations that everything is constantly moving further from us, the further out you go, the faster it's moving away.
But everything is moving from everything, including itself.
I do apologize if I'm a little muddy, I did my physics degree about a decade ago.
Edit as for why gravitational waves travel at the same as E&M waves is because "information" is what travels at the speed of light. For an electro magnetic wave that's disturbances in E&M. For gravity that's ripples in the fabric of space-time. For quantum there's experiments showing that entangled particles will collapse together, if sperated by distance, the lag time is also the speed of light.
EDIT 2:
The only thing faster than the speed of light, is actually the expansion of the universe beyond a certain distance. Don't remember what it is. But because distance istself is expanding, that's proportional to distance. So the expansion rate is actually faster than the speed of light far enough out. But no SINGLE point is expanding faster than the speed of light.
If there's no such thing as absolute distance, then how can you say that a metre bar (and the metre) is larger than it used to be?
If distance is relative, and matter isn't expanding relative to anything else, then matter isn't expanding.
We ultimately define distance in terms of c, and the fundamental forces agree with this. We do not observe atoms expanding, but we do observe the space between galaxies expanding. Presumably the space we occupy is also expanding, but it's such a small effect as to be irrelevant.
Back to my original question, is the boundary between irrelevantly small and detectable above or below the galactic scale?
I think the trouble is also partly based around thinking of then universe as a volume, which implies a centre. And that's where this analogy falls apart.
Because everything is expanding from everything, there is no centre. YOU are always centre. So you are "expanding" but you don't change volume.
This is why I keep saying space isn't getting bigger, distance is.
It's not that a sheet of paper becoming bigger so the grid paper becomes larger,. It's changing it's distance of something, not it's size and shape.
We don't observe galaxies getting bigger. We observe them constantly moving away from us. Even. When they're moving to us, but it's done at a slower pace than expected. The further away you are, the faster you move away. And it's a universal constant of 73km/s/Mpsc.
Notice that is a speed per distance. It's not saying space is getting bigger, it's saying things are moving faster away from you the further you go away.
The universe isn't expanding like a loaf of bread because it has a volume. It's expanding from one volume to another. Where the universe doesn't.
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.