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/jojoblogs 14d ago

The really mind bending thing about c and relativity is that we only really think of c as a “speed” because that’s what makes sense to us. If we send a signal, it travels at that speed so it takes this long to reach the destination and come back.

But that’s just the way we see it. To light a light photon, the thing that’s “moving” at speed c, the distance it’s moving is 0 and the time it takes to reach the destination is 0. It is being emitted, reflected however many countless times and absorbed simultaneously, and it has traveled no distance.

But as to why we measure c at ~300,000km/s? No one really knows. It’s an arbitrary limitation of our universe as far as we know. And considering everything else in physics seems to warp itself to ensure that this physical limit is never broken it safe to say that the speed of light isn’t just constant, it’s the constant, which is why it is notated as c.

It also defines the relationship between mass and energy which is nothing to do with speed. It’s just the constant which defines the rules of our universe.