[olddustytrail]

Rotation isn't relative. You can tell how quickly you're rotating without reference to any other objects.

[carra]

But even then you can only tell that you are rotating relative to space itself. If I understand correctly here we are speaking about the space itself rotating, so that would not be possible unless something else contains our universe's space, right?

[olddustytrail]

Nope, rotation is not relative because it's an acceleration.

There is no "space itself" because then you're assuming it is relative, like the speed of light. Basically you're trying to rediscover the aether.

That was the question: light moves at speed C, but relative to what?