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-   -   Rotation of the universe? (http://www.physicsforums.com/showthread.php?t=503729)

novop Jun2-11 06:17 PM

Rotation of the universe?
 
Hi all,

I understand that there are several solutions to Einsteins equations that consist of a rotating universe. I have a few questions. If the universe is composed of everything that exists, how can the universe rotate in the absence of space, since all space is contained within the universe? And, as a Machian, how can the universe rotate if there is nothing for it to rotate relative to (no "fixed stars", as in the case of Newton's bucket). Also, would rotation of the universe imply an axis of rotation, and if so, couldn't this be construed as a preferred frame of reference?

Drakkith Jun2-11 10:08 PM

Re: Rotation of the universe?
 
See here for another thread on this: http://www.physicsforums.com/showthread.php?t=217956

novop Jun3-11 12:21 AM

Re: Rotation of the universe?
 
I looked at it, and couldn't find any decisive answers.

Drakkith Jun3-11 12:37 AM

Re: Rotation of the universe?
 
Hopefully someone can help you. Until then just keep searching around the internet.

novop Jun4-11 03:31 PM

Re: Rotation of the universe?
 
bump ^.^

Blibbler Jun5-11 02:29 PM

Re: Rotation of the universe?
 
Maybe a better way of framing the question could be to ask if the universe has overall angular momentum or if the sum of all angular momenta in the universe is zero.

Then we're back to Mach, back to Einstein and back to the idea of relativity versus absolutism.

We instinctively think in absolute terms and this is what GR shows we cannot afford to do as it leads to questions such as the one you posed!

You have presented a false dichotomy on the premise that there is an intrinsic difference between there being angular momentum in the universe and the universe itself spinning. There isn't: as you correctly state, the universe contains everything, including all angular momentum. The logical conclusion is that while parts of the universe can spin relative to one another the concept of the universe having overall angular momentum, and therefore spinning, is meaningless as it beggars the question "relative to what?". Assume the universe to be a zero sum game and meditate from there.


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