  Magnetic fields may have been generated in the electroweak phase transition
through spontaneous symmetry breaking or through the subsequent dynamical
evolution of semiclassical field configurations. Here I demonstrate explicitly
how magnetic fields emerge spontaneously in the phase transition also when no
gradients of the Higgs field are present. Using a simple model, I show that no
magnetic fields are generated, at least initially, from classical two-bubble
collisions in a first-order phase transition. An improved gauge-invariant
definition of the electromagnetic field is advocated which is more appropriate
in the sense that it never allows electrically neutral fields to serve as
sources for the electromagnetic field. In particular, semiclassical
configurations of the Z field alone do not generate magnetic fields. The
possible generation of magnetic fields in the decay of unstable Z-strings is
discussed.
