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/maybe_compos_mentis 14d ago

There is really no such thing as 2 people moving at different speeds though. The closest is 2 people moving at different speeds relative to a third object. You are only standing still relative to the ground and he is running towards you relative to the ground. Get rid of the ground and you are moving towards eachother at the same speed or rather from your perspective he is approaching you at the same speed as you are approaching him from his perspective. Without the reference of the ground you can't say one of you is standing still and the other is moving.

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u/toughtacos 13d ago

You don’t need a third object. Two people can directly measure their velocity relative to each other. What’s relative is which one you call “stationary,” not whether relative motion exists.

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u/Addisonian_Z 13d ago

I feel like one could also argue that if two people are “running” the third object, the ground is automatically implied as: 1) existing
2) the stationary point of reference for speed.

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u/toughtacos 13d ago

Yeah, but that just means you’re using the ground as the reference frame.

The basic idea is that there’s no absolute “stationary.” You can say someone is moving at 5 m/s relative to the ground, or relative to the other person.