On Wednesday, January 29, 2020 at 2:57:25 AM UTC-6, Alan Grayson wrote:
>
> Considering the distant galaxies, they're receding at near light speed. So
> according to SR, their clocks should be ticking at a much slower rates
> than, say, a local clock in our galaxy. OTOH, there's a physical clock for
> the entire universe; namely, the temperature of the CMBR. If we tell time
> by this clock, all clock readings of all galaxies are identical. So which
> is it? Are clocks in distant galaxies running slower than a local clock in
> our galaxy, or are both clocks running at the same rate? TIA, AG
>
The physics with distant galaxies is general relativistic, not special
relativity. The redshift factor v = Hd, in the near linear form, has the
redshift factor v/c = z = Hd/c. In the FLRW metric this is a bit more
general with z = e^{Ht} - 1, where for small HT << 1 then t = d/c and z =~
Ht. The reshift factor for the CMB is z = 1100, which means that anIR
photon with wavelength 1000nm is expanded to 1100 microns, or a millimeter.
The peak of the CMB blackbody radiation is 160 GHz and this was produced by
radiation peaked at 17.6x10^{4}GHz. This is in the IR region with a
wavelength of 5,87x10^{-5}cm, in the IR, The z multiplicative factor is the
same as a time dilation, where we can think of these red shifted photons
are representing the slowdown of clocks (clocks being the quantum
oscillations of atoms etc) in this surface of last opaque scatter.
LC
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