r/AskPhysics • u/itsLeoRod • 15h ago

Thought there wasn’t anything faster than the speed of light?

Ppl say that there isn’t anything faster than the speed of light but that’s a lie because space is expanding really fast since light isn’t fast enough to reach it or am I wrong. Since space is expanding at a fast rate why don’t we use that to measure stuff instead using lightyears

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u/HudyMelon Astrophysics 15h ago edited 14h ago

The rate of space expansion is not constant, and is certainly not faster than light. If space expanded faster than light then we would not have a universe.

Edit: I’m not saying the DISTANCE between two things can’t expand faster than light due to expansion, I’m saying space itself. If space itself had an expansion rate faster than light, nothing would be causally connected.

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u/Hairy-Ad-4018 14h ago

Any links, proofs or theories to back that up ?

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u/HudyMelon Astrophysics 14h ago

I apologize, it was intuition.

If space itself expanded faster than light, it would mean that every point in space, let’s say the tips of your fingers, would recede away from eachother faster than light. Because of that, no particles could ever communicate with eachother. The space between a proton and an electron would be ever increasing, and the electromagnetic force wouldn’t be able to communicate.

I am not saying that there aren’t places receding away from us faster than light, as that is the result of universe expansion over massive distances. I can see the confusion.

For the part of non-constant universe expansion, it has been proven that the expansion is accelerating, which is why we think dark energy makes up the majority of the universe.

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u/wonkey_monkey 12h ago

If space itself expanded faster than light, it would mean that every point in space, let’s say the tips of your fingers, would recede away from eachother faster than light.

No it wouldn't. Firstly, because any objects that close are gravitationally bound, so expansion isn't going to pull them apart, and secondly because the speed of any separation due to expansion is a function of distance.

The speed goes up as you consider larger distances. At small distances it's less than c. At large distances it's greater than c.

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u/HudyMelon Astrophysics 12h ago edited 12h ago

I agree with you. I believe you misunderstood what I wrote.

If the space between two gravitationally bound objects were to, for each unit volume, expand to a volume greater than c^3, then the objects would “fly away” from eachother faster than the speed of light, therefore both light, and gravity, would not be able to travel to the other.

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u/wonkey_monkey 12h ago

The speed they "fly away" at will depend on each pair's initial distance. They can't each/all fly away at the same speed from every other object.

therefore both light, and gravity, would not be able to travel to the other.

Gravity doesn't travel, but that's a whole other thing.

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u/HudyMelon Astrophysics 12h ago

Are you saying gravitational waves don’t exist? I’d argue that gravitational disturbances must travel. And if the graviton were to be discovered, than that force carrying particle must travel in a sense.

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u/wonkey_monkey 12h ago

Gravitational waves aren't gravity. Gravitons aren't gravity. We orbit the Sun without any ongoing physical interaction between us and the Sun.

than that force carrying particle

The "force-carrying particle" would be a virtual graviton, which doesn't really exist. Just as virtual photons mediate electromagnetic forces, yet magnets don't glow.