By the Book 6

Ok so if you look graph the density graph you will see that before the radiation era there comes the lepton era! You remember what leptons are, don’t you? They are the things that aren’t made of quarks, like electrons and tauons. This era begins when the universe is 100 microseconds old, that is .0001 seconds old. And the temperature was a trillion Kelvin or 100,000,000,000 Kelvin. Oh, and it was really really dense! Apparently this is when electron pairs where created. I might have talked about this before. So this is when two electrons (an electron and a positron) where spontaneously created from some energy (usually in the form of a photon) and then they get annihilated when they run back into each other. And it wasn’t just electrons it was tauons and muons and their neutrinos and all various forms of leptons. But this was happening all around so quickly and there was so much energy to create them with so the universe was a frothy mix of energy and leptons.