The Origin of Cosmic Magnetic Fields

In this talk, I review a number of particle-physics models that lead to the creation of magnetic fields in the early universe and address the complex problem of evolving such primordial magnetic fields into the fields observed today. Implications for future observations of the Cosmic Microwave Background (CMB) are discussed. Focussing on first-order phase transitions in the early universe, I describe how magnetic fields arise in the collision of expanding true-vacuum bubbles both in Abelian and non-Abelian gauge theories.