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The following quote has no reference: "Like the cosmic microwave background radiation (CMB), the CνB is a relic of the big bang; while the CMB dates from when the universe was 379,000 years old, the CνB decoupled from matter when the universe was two seconds old. It is estimated that today, the CνB has a temperature of roughly 1.95 K."
I would very much like to understand the assumptions made and the method used to calculate the numbers used in the quote, especially the "two seconds old" and "1.95 K" numbers. The article explains the derivation of the 1.95 number, but not the assumptions. My guess is that the assumptions include an assumption that the temperature varies inversely with the a(t) (the scale factor for the expansion) as is so for photons. However, that assuption assumes a state of equibrium, which is generally acknowledged to be false after the period of nuclear synthesis. If a neutrino has any rest mass, then the temperature would vary inversely with the square of a(t). (See http://arxiv.org/abs/0808.1552 Note on the thermal history of decoupled massive particles, Hongbao Zhang. Also see the discussion on the physics forum: https://www.physicsforums.com/threads/how-does-a-particles-kinetic-energy-vary-with-a-t.811627/ )
I would hope that the author of the article would be able to provide a reference that would include this information about assumptions and methods. BuzzBloom (talk) 14:23, 3 May 2015 (UTC)