  Helical intergalactic magnetic fields at the $\sim 10^{-14}~{\rm G}$ level on
$\sim 10~{\rm Mpc}$ length scales are indicated by current gamma ray
observations. The existence of magnetic fields in cosmic voids and their
non-trivial helicity suggest that they must have originated in the early
universe and thus have implications for the fundamental interactions. I combine
present knowledge of the observational constraints and the dynamics of
cosmological magnetic fields to derive characteristics that would need to be
explained by the magnetic field generation mechanism. The importance of CP
violation and a possible crucial role for chiral effects in the early universe
are pointed out.
