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TransparentMastering t1_jb0ya8q wrote

Reply to comment by Aseyhe in Does the age of the universe depends on where you are? by _bidooflr_

How is the rest frame of the CMBR determined if light travels at the same speed in all reference frames? Is it to do with the red and blue shift?

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Aseyhe t1_jb0yzuq wrote

It's the center-of-momentum frame for all of the CMB photons (within some volume of space), not the frame of individual photons. It's also the frame in which the CMB temperature is the same in all directions. If you're moving with respect to that frame, you'll find that the CMB is hotter (blueshifted) in the direction of your motion and colder (redshifted) in the opposite direction. That's what we find, and the magnitude of this effect tells us that we are moving at 370 km/s with respect to the CMB.

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Void_vix t1_jb2ssty wrote

So accelerating with respect to any other object causes the CMB to Doppler shift for the observer?

Wouldn’t that mean that a truly non inertial frame would have to be at the center of a mass?

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