Abstract:
It is noted that the processes of phase transition in equilibrium statistical mechanics and onset in thermoacoustic engines have the same mathematical features, and arise in the same way from the trace over a statistical density matrix. Onset differs physically in being a process of spontaneous breaking of time-translation symmetry, while equilibrium critical systems are by definition time independent. Heat engines thus represent a class of systems through which the concept of phase transition may be extended to include a limited range of classical dynamics.