This section is organized to track the chronological
events in the history of the early or relativistic Universe,
focusing mainly on four defining moments:
1) the Big Bang singularity and the dynamics of the
very early Universe; 2) inflation and its generic nature;
3) QCD phase transitions; and
4) primordial nucleosynthesis
and the freeze-out of the light elements.
The late or post-recombination epoch
is reserved to a separate section § 4.