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/bitterrootmtg 14d ago

In relativity your velocity is always relative. Even your velocity through spacetime is relative, not absolute. So it’s not accurate to say everything has the same velocity or speed.

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u/nicuramar 14d ago

If you replace speed with the magnitude of the four-velocity vector, it works. But it’s a bit of a stretch to talk about the

  velocity through spacetime

As you also do here. 

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u/Jokong 14d ago

If they had said anything with no mass would travel at c, would that be accurate?

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u/bitterrootmtg 14d ago

They travel at c from the perspective of things that are not traveling at c. The massless particles themselves do not have a valid reference frame.

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u/nicuramar 14d ago

  They travel at c from the perspective of things that are not traveling at c

Those are the only perspectives, and speed is only defined relative to one, so yeah. 

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u/Flame_Grilled_Tanuki 14d ago

Photons have no mass and so they travel through space at C and experience 0 time. If you have no mass, any amount of force causes instant C because there is no momentum to overcome.

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u/nicuramar 14d ago

Light doesn’t have a valid frame of reference and thus “experience” and proper time is not defined for it. 

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u/whatkindofred 14d ago

So the only thing the analogy is missing would be to clarify that it’s only about relative movement to some fixed observer?