
What Is the Cosmic Microwave Background? - xref
https://www.universetoday.com/135288/what-is-the-cosmic-microwave-background/
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gmiller123456
I think this is a simpler and more complete explanation: "The cosmic microwave
background (CMB) is an almost-uniform background of radio waves that fill the
universe" [1]

[1]
[http://cosmology.berkeley.edu/Education/CosmologyEssays/The_...](http://cosmology.berkeley.edu/Education/CosmologyEssays/The_Cosmic_Microwave_Background.html)

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sunstone
It's the quantum radiation finger print left over from when the entire
universe was smaller than a billionth of a proton and about to get _very_ much
bigger almost instantaneously. (the poetic version)

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madeuptempacct
Ironically, I had the same question. I don't really get it after reading the
Wikipedia page after seeing it in the Three Body Problem.

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v_lisivka
Just light from distant galaxies? Light is moving at C, so it cannot age
because it experiences no time, but it's not always the case.

Light must age, otherwise our infinite Universe, which exists for infinity,
will produce infinite^2 amount of light, which is not possible.

Current explanation of light aging is stretching of space in all directions.
However, same effect can be explained by local random stretching of space
when, for example, virtual pair of quantum particles emerges and then
disappears. Casimir effect is pretty strong, which indicates that our space is
very bumpy, full of white noise.

(Beware: non-native speaker).

