In Kolb and Turner's Early Universe, (see here) it is mentioned that

Variation in the CMBR temperature in different directions is expected due to several effects: the motion of our local reference frame with respect to the cosmic rest frame (i.e., the FRW frame), rotation of the Universe, ...


1. As far as I know, the FRW frame is a coordinate "grid" attached to the expanding universe itself. In this coordinate system, the galaxies drifting along with the systematic expansion, sit at fixed coordinates at all times. What is meant by a local reference frame as opposed to the FRW frame? In this context, does it refer to the satellites that are up in the sky for measuring CMBR anisotropy?

2. Is there a conclusive evidence that the Universe rotates? Is there a preferred axis then?


Galaxies have proper motion relative to the CMB, the sun rotates around the galactic center, the earth rotates around the sun, see here.

  • $\begingroup$ Aren't the galaxies drifting with the systematic expansion of the Universe having a fixed comoving coordinate? @Thomas $\endgroup$ – SRS Mar 14 '18 at 4:58
  • $\begingroup$ Galaxies form clusters, undergo collisions, fall towards super-clusters etc. Of course. on average, they just participate in the expansion of the universe. $\endgroup$ – Thomas Mar 14 '18 at 14:58
  • $\begingroup$ My question was What is meant by a local reference frame? Can you illuminate? @Thomas $\endgroup$ – SRS Apr 4 '18 at 22:02
  • $\begingroup$ The FRW frame is attached to the CMB, and the local rest frame is attached to the earth (or the sun, or the galaxy, depending on what kind of motion you explicitly correct for). $\endgroup$ – Thomas Apr 5 '18 at 1:25

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