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> the uniform ultimate backdrop we have when looking in any direction

Is the CMB exactly uniform in every direction? Or is this early light slightly more redshifted when we look up versus when we look down or left or right? Does the oldest light we see in any given direction vary slightly in color?

I'm imagining the universe expanding as a sphere from a central point, but we're located off-center. Wouldn't the early infrared photons emitted from the other side of the central point of expansion from us be observed by us now as a slightly different color than the early infrared photons emitted closer to the edge of the early expanding universe?

A rabbit hole of questions: - When did space start expanding? - Did it have to rapidly expand for 400k years as extreme forces propelled matter apart? - Was that expansion faster or slower than the current expansion of space between galaxy groups? - Is expansion uniform across the universe? - Or is expansion slower closest to the original center of the universe? - Maybe there's a central point in the universe that's not moving relative to a reference frame outside our universe? - Is space discrete or continuous? - As space expands do new "units" of space appear between units of space that have grown farther apart? - If not, wouldn't physics work differently for areas of space where the units of space have grown farther apart than areas of space where the units of space aren't as far apart?



The CMB is famously not exactly uniform https://www.esa.int/ESA_Multimedia/Images/2013/03/Planck_CMB

I have not read that any particular directions are evident in the sense you suggest though.


There is a very obvious dipole in the CMB due to our peculiar velocity. This has been removed in almost all images you saw because it's just an artifact of our particular movement and not physical. It's just the Doppler effect.

This page has three pictures: https://wmap.gsfc.nasa.gov/universe/bb_cosmo_fluct.html

The first is the actual observation. It's boring and looks completely homogeneous.

So you subtract the average value, which brings you to the second picture. Its temperature is 0 on average, but shows the obvious dipole.

When you remove the dipole, you get the last picture, which show only the physical temperature fluctuations.


that is a very clear explanation


Better to think of expansion as being a 2D dot on a balloon.

As balloon expands, in all directions there is same rate of expansion. You are not inside the balloon close to one side to observe the difference.




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