NEUTRINOS IN THE UNIVERSE

This neutrinos cosmic background radiation comes from the decoupling of the neutrinos, which, until universe became sufficiently cold, were appearing and disappearing, absorbed by protons or emitted by neutrons. At a given temperature of the universe, about 1 second after the Big-Bang, protons have only a weak probability to absorb a neutrino, which thus decouple.
Some hundreds of thousand of years later, photons will decouple the same way from charged particles like the electrons and will become the light cosmic background radiation at 2.73 degree Kelvin.

The theory estimated also the neutrino density in the universe: about 110 per cm³, for each neutrino family, that means 330 neutrinos per cm³ as a whole. 330 millions per m³. This is quite lot!... By comparison, you find a mean of 0.5 proton and one billion photons per cubic meter of universe. Thus, you find about one billion more neutrinos than protons. And those Big-Bang neutrinos are approximately as numerous as the Big-Bang photons. The matter, which composes us (protons, neutrons, electrons) is not very important... quantitatively.