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In physical cosmology, the lepton epoch was the period in the evolution of the early universe in which the leptons dominated the mass of the universe. It started roughly 1 second after the Big Bang, after the majority of hadrons and anti-hadrons annihilated each other at the end of the hadron epoch. During the lepton epoch the temperature of the universe was still high enough to create lepton/anti-lepton pairs, so leptons and anti-leptons were in thermal equilibrium. Approximately 10 seconds after the Big Bang the temperature of the universe had fallen to the point where lepton/anti-lepton pairs were no longer created.[1] Most leptons and anti-leptons were then eliminated in annihilation reactions, leaving a small residue of leptons. The mass of the universe was then dominated by photons as it entered the following photon epoch.

Astronomy: The Big Bang. The Lepton Era

References

^ The Timescale of Creation

Allday, Jonathan (2002). Quarks, Leptons and the Big Bang. Second Edition. ISBN 978-0750308069.

Timeline of the Big Bang
Augustinian era · Big Bang · Planck epoch · Grand unification epoch · Electroweak epoch (Inflationary epoch, Reheating, Baryogenesis) · Quark epoch · Hadron epoch · Lepton epoch · Photon epoch (Big Bang nucleosynthesis, Matter domination, Recombination) · Dark ages · Reionization

Astronomy Encyclopedia

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