thelastestgunslinger t1_j9ryud9 wrote

There’s a really interesting article about this on

The really interesting thing is that special relativity (which is what says nothing can move faster than light) is about local spacetime, because it requires a local frame of reference. General relativity governs non-local references, and it’s indifferent to the speed of light.

> The notion of the absolute speed limit comes from special relativity, but who ever said that special relativity should apply to things on the other side of the universe? That's the domain of a more general theory. A theory like…general relativity.

It's true that in special relativity, nothing can move faster than light. But special relativity is a local law of physics. Or in other words, it's a law of local physics. That means that you will never, ever watch a rocket ship blast by your face faster than the speed of light. Local motion, local laws.

But a galaxy on the far side of the universe? That's the domain of general relativity, and general relativity says: who cares! That galaxy can have any speed it wants, as long as it stays way far away, and not up next to your face.

It goes deeper than this. Concepts like a well-defined "velocity" make sense only in local regions of space. You can only measure something's velocity and actually call it a "velocity" when it's nearby and when the rules of special relativity apply. Stuff super-duper far away, like the galaxies we're talking about it? If it's not close, it doesn't count as a “velocity” in the way that special relativity cares about.

Special relativity doesn't care about the speed — superluminal or otherwise — of a distant galaxy. And neither should you.

If I think about it too much i start to dislike it. But there it is (probably significantly oversimplified for laypeople).