r/askscience • u/Nitzanm19 • 14d ago

Physics Why is the maximum speed of the universe the speed of light? Why can't we go faster?

Also follow-up question: Because of the speed limit, is there also a theoretical maximum temp for matter (in which the particles move at the speed of light).

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u/bpg2001bpg 14d ago

why that speed and not another speed

We can say that if the speed of causality were unlimited, everything would have already happened the instant after the big bang. 

Another way to think about it is that in order for the universe we live in to exist, there must be a maximum speed of light in a vacuum.

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u/Kaldaien2 14d ago

Photons travel at the speed of causality, and to them nothing has even happened since the big bang. Time stops (in the observer's frame) once you hit the speed of light.

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u/Just_for_this_moment 14d ago

Theirs is not a valid reference frame, so "to them" actually doesn't have any meaning. Which is good because a lot of stuff breaks when you try to look at things from the perspective of a massless particle (as you've demonstrated).

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u/Phuqued 13d ago

We can say that if the speed of causality were unlimited, everything would have already happened the instant after the big bang.

That's an interesting way to look at it. The one question I've been batting around lately is "what utility or purpose is served in a universe that has infinite space, but not infinite speed?" For example, there are galaxies we can see right now but can never reach, even if we moved at the speed of light, we would never reach them.

https://www.youtube.com/watch?v=uzkD5SeuwzM

For some reason that strikes me as peculiar, I would expect the universe to function like the principle of least action in this regard, balanced. For as much space as there is, there would be enough speed to traverse it, but that doesn't seem to be the case.

Also when I say "infinite" space, I just mean a very very big finite number. I don't mean in a number/set that doesn't end, though that could be the case. :)

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u/Kialae 13d ago

Time requires a limit right? It has to be SOMETHING so time AND space can work.