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Suppose in the universe, there are inertial frames in the vicinity of galaxies. Suppose also that these frames rotate slightly with respect to each other - that the universe is not quite a 'mill pond'.

If this were true, our Galaxy would have its own inertial frame, rotating wrt distant galaxies.

The rotation of our galaxy's frame would affect astronomical observations.

Does anyone know the upper bound on the rotation rate of our galaxy's inertial frame which is consistent with observations?

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  • $\begingroup$ I think you're asking if there is a net rotation of the universe about us. Is that so? $\endgroup$
    – John Rennie
    Commented Oct 7, 2017 at 14:47
  • $\begingroup$ That is how it would appear, though I am explicitly not asking if the universe as a whole is rotating. $\endgroup$
    – RERT
    Commented Oct 7, 2017 at 15:25
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    $\begingroup$ Your second supposition has no physical meaning. Two inertial frames cannot rotate relative to each other. $\endgroup$
    – safesphere
    Commented Oct 7, 2017 at 15:32
  • $\begingroup$ This is in the context of general, not special relativity. I think it would be easy to write down a metric with a central zone an inertial frame which was rotating relative to another inertial frame at infinity. Harder I admit to be sure that the field equations were satisfied in the evolution of the system over time. But that is all moot if the experimental bound is too small to be interesting. @safesphere $\endgroup$
    – RERT
    Commented Oct 7, 2017 at 21:15
  • $\begingroup$ Sorry, my first question @John Rennie $\endgroup$
    – RERT
    Commented Oct 7, 2017 at 21:18

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I'd just like to cross-reference the top answer to the question What if the universe is rotating as a whole. The detection level there is given as 10^-9 to 10^-15 rads/year, so roughly 10^-16 to 10^-22 rads/sec.

Yes, it isn't answering the same question I asked, but it is a place to start until there is a better answer.

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  • $\begingroup$ I've linked the question for you. $\endgroup$
    – John Alexiou
    Commented Oct 12, 2017 at 11:24

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