Does Big Bang theory predict a cosmic background radiation different than the 2.7 K actually found?
No. One of the fundamental tests of Big Bang cosmology is that it predicts the right temperature for the universe relative to the age of the universe. Now, I do not mean the right temperature to millions of decimal places, but I do mean that Big Bang cosmology does predict a 2-3 K background radiation temperature given its age of 10 – 15 billion years ( current expansion rate), and the measured primordial element abundances which are sensitive to how hot the universe was when its density was high enough for nucleosynthesis to happen. The perfect black body character of the cosmic background radiation, shown in the data and curve above, was a spectacular triumph for Big Bang theory. What we still do not fully understand, and what Big Bang cosmology does not offer, is an explanation for the isotropy of this radiation. It is true that Big Bang cosmology is a cosmology based on a homogeneous and isotropic expansion of the universe, but we do not understand how regions of the sky farther ap
