What do the relic photons show?

Coming to us from causally disconnected regions in all directions

The size of the horizon, or the causally connected region of the universe at the moment of the last interaction of relic photons, though stretched 1,100 times now, is only one-thirtieth of today’s horizon and has an angular size of about two degrees. Thus, we see about 30 thousand causally disconnected regions of space, each of which might have quite different temperature, while the temperature of the relic photons in all directions differ only in a few hundredths of a percent. The photons had separated from substance and imprinted the temperature of the era when concentration of atoms in the universe has fallen to 300 per cubic centimeter due to expansion of the universe, and the time of flight of photons to interact with one of those free electrons and protons remaining in space exceeded the pace of expansion.

Relic photons show early universe

While it might be otherwise — the universe would not be isotropic.


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