Why cannot the universe have net angular momentum?

Kurt Godel found a solution of Einstein's GR equations in which the universe was rotating. Each point has an equal claim for being the center. In such a universe time travel is theoretically possible. Observations show that our Universe does not rotate in such a way.

 

That is a sum of local rotations, not a global rotation. You could say is is a net angular momentum. It is not a terribly firm result though, and I'd forgotten about it.

 

The question is what would you measure the angular momentum of the universe against, assuming it had any?

 

If the universe is rotating, it does so at a very leisurely pace - re: Is the Universe Rotating http://arxiv.org/abs/0902.4575

 

I did laugh when I read that. That is funny.

I suppose what they would mean is that if you are stationary at the edge you would have an error between the total gravity you feel toward the center compared to measuring all the mass in the universe and doing the calculation on paper.

 

We have a FAQ about this: https://www.physicsforums.com/showthread.php?t=506988 [Broken]

It doesn't make sense to describe it as having a (zero or nonzero) angular momentum, because angular momentum isn't defined or conserved globally in GR. You can describe it as having a zero or nonzero angular velocity.

 

There is also a thread on this - https://www.physicsforums.com/showthread.php?t=217956