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.
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.
== See also ==
Chronology of the universe
Big Bang
