neutrino decoupling

During this event, which lasted for about ten seconds, neutrinos 'decoupled' in that they no longer interacted with any other matter, they moved freely to fill the universe. As such, there should have been a neutrino as well as microwave background to the universe.

An effect of this was that protons and neutrons could no longer transform into each other, freezing their ratio at 6 protons to each neutron.

Neutrinos: Very light (possibly massless) particles that are emitted in the process of radioactive decay. There are three species, associated with electrons, muons, and tau-leptons. They interact with ordinary matter through the weak force.

- ASh, Fx (ed)