  In first-order phase transitions in the early universe, the bubble wall is
expected to be significantly slowed-down by its interaction with the
surrounding plasma. We examine the behaviour of the phase of the Higgs field
after two-bubble collisions, and find that phase differences equilibrate much
more quickly in slow-moving bubbles than in those which expand at the speed of
light. This could lead to a significant reduction in the initial density of
topological defects formed at a first-order phase transition.
