background observatories promises to give us precision measurements of key
parameters which are set in the very early universe. For example, we may
soon know to fair precision the amount of relic relativistic energy and
the deuterium and helium abundances set during the time when the neutrinos
fall out of thermal and chemical equilibrium. Given the excitement and
ferment right now surrounding new ideas in dark matter and other beyond
standard model (BSM) physics, we would very much like to leverage these
coming measurements into deeper insights into this epoch, in effect
turning the early universe into a precision BSM physics laboratory. Doing
so, however, requires theorists to "raise their game" in modeling the
neutrino decoupling epoch. We will discuss these issues and reveal some
surprising features of the universe when it was roughly one second in age.