Making Magnetic Fields on Cosmic Scales

Magnetic fields are observed very early in the evolution of structure of the universe. It is not known how or when these fields were created. I will discuss the various theories of the field origin and the fluid mechanical issues that arise. Small scale fields of observable amplitudes are relatively easy to create on short time-scales by turbulent flows or compact objects. The central issue is the the creation of the observed long scale coherence in the field.