Cosmic microwave background

The cosmic microwave background (CMB) is electromagnetic radiation left over from an early stage of the universe. The accidental discovery of the CMB in 1965 by American radio astronomers Arno Penzias and Robert Wilson earned them the 1978 Nobel Prize in Physics, because it is evidence of the Big Bang origin of the universe.

This is the farthest we can now observe with electromagnetic sensors back to a time when the universe was about 300,000 years old, when matter and radiation finally “decoupled”.

We find that there is roughly one proton in the universe today for every 10 billion photons in the CMB. This means that the original excess of protons over antiprotons was only about 1 part in 10 billion! This would have been sufficient to have produced all the observed matter in the universe and how it got to be made of matter and not antimatter.