In the framework of the Summer School on Cosmology (smr3945), Professor Gruzinov is giving a special seminar on the origin of cosmic magnetic fields.

It is often claimed that the very existence of galactic and especially intergalactic magnetic fields proves that the cosmic magnetic field is primordial, and thus BSM physics is required to explain its origin. These claims are based on a simple misunderstanding of classical physics and astrophysics.
We show how the first cosmic magnetic fields  (likely) appeared in the first  baryonic halos. The observed galactic and intergalactic fields then pose no immediate problem. But, as nobody knows the ultimate, better constraints on primordial magnetic fields will always be of interest.