The standard hot Big Bang model predicts a background of neutrinos
permeating all space. At an average of 330 neutrino per cubic
centimetre, the relic neutrinos are the most abundant known particles in
the universe. However, unlike its better-known cousin, the cosmic
microwave background, the direct detection of this relic neutrino
background has so far eluded us. Nonetheless, because of the sheer
enormity of their collective gravitational forces, these relic neutrinos
have a strong impact one the many phases of the universe's evolution.
In this talk I will discuss some of the ways in which neutrinos
influence the evolution of the universe on the largest scales, and how
we can use this understanding in combination with cosmological
observations to learn about neutrino physics in the early universe.