This section is organized to track the chronological events in
the history of the early or relativistic Universe; we focus
mainly on four defining moments in our current understanding of
the classical picture: 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
.