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Why cannot the universe have net angular momentum?

  1. Sep 28, 2012 #1
  2. jcsd
  3. Sep 28, 2012 #2
    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.
     
  4. Sep 28, 2012 #3
    thank you. then what of the results that show a tiny net angular momentum in terms of galaxy spin axes?
     
  5. Sep 28, 2012 #4

    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.
     
  6. Sep 28, 2012 #5

    Chronos

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    The question is what would you measure the angular momentum of the universe against, assuming it had any?
     
  7. Sep 28, 2012 #6
    does angular momentum have to be relative to anything external though? it can be relative to itself. it can be measured by inertial forces such as the centrifugal force or Coriolis force and how they affect, say, the motion of gyroscopes within an object with angular momentum.
     
  8. Sep 28, 2012 #7

    Chronos

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  9. Sep 28, 2012 #8
    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.
     
  10. Sep 28, 2012 #9

    bcrowell

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    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.
     
    Last edited by a moderator: May 6, 2017
  11. Sep 28, 2012 #10

    Chronos

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