  Phase transitions in the early universe are prime settings for the production
of primordial black holes, since they can break the relatively quiescent
homogeneity and isotropy of Friedmann-Robertson-Walker (FRW) cosmologies. These
epochs of "symmetry breaking," moreover, can affect the subsequent development
of spacetime by changing the evolution of some FRW parameters, including the
present age and density of the universe. We discuss the relative importance of
such effects on constraining mechanisms of black hole formation.
