Main Question or Discussion Point
Can anyone explain how the cosmic microwave background radiation (CMBR) "cooled"...I'm supposing that about 300,000 years or so after the bang, when the universe became transparent, things were hotter than 2.7 degrees above absolute zero we observe today....
So an expanding universe redshifts light, and in doing so CMBR loses energy?? Does this mean the "new space" created by expansion would otherwise be at absolute zero but is being warmed by a finite amount of CMBR?? So if the universe were not expanding, would the CMBR be at the same temp as it was when the universe was about 300,000 years old.The photons that existed at that time have been propagating ever since, though growing fainter and less energetic, since the exact same photons fill a larger and larger universe.