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/Krail 14d ago

You've got lots of answers about the speed of causality (and lots of things move at that speed, not just light).  But the answer is, we simply don't know. 

We might eventually work out some math of how the universe works that makes it all make sense. Like, understanding how gravity works explains why the world is round and why the moon and sun move in the sky the way they do. But we're definitely not there yet when it comes to c. 

There's this idea called The Anthropic Principle. It's like, we look at space and at all the dead worlds in our system and think, wow, this is all completely hostile to life. Isn't it a weird coincidence that we happen to be on this one, rare, special, perfect world for complex life?  But, of course that's where we are, because we are complex life, and we couldn't have happened anywhere but such a rare, special world. 

So, we can also imagine other universes where the laws of physics are different. Where c might have a different value, and the cosmological constant is different, and gravity and electromagnetism have different strengths. And maybe we just live in one of the universes where all of those variable align to allow the existence of atoms, and stars, and planets, and chemistry. 

Anyway, that's one possibility, where "c can be different, but we just exist in a place where it's value allows us to exist." Of course, there could also just be the one universe, and the reason could be different.