  We discuss here phase transitions in quantum field theory in the context of
vacuum realignment through an explicit construction. Vacuum destabilisation may
occur through a scalar attaining a nonzero expectation value, or through a
condensate mechanism as in superconductivity and for chiral symmetry breaking,
or by some other mechanism not taken here. Phase transition is defined as
vacuum realignment with a discontinuity in some observables which correspond to
the classical order parameters. The method is nonperturbative and variational,
using equal time algebra and an ansatz for the construction of the physical
vacuum.
