Superfluidity and space-time translation symmetry breaking.
I present a simple model that exhibits a temporal analogue of superconducting crystalline (Larkin-Ovchinnikov-Ferrell-Fulde) ordering, with a time-dependent order parameter. I sketch designs for minimally dissipative ac circuits, all based on time translation symmetry (τ) invariant dynamics, exploiting weak links (Josephson effects). These systems violate τ spontaneously. I also discuss effective theories of that phenomenon, and space-time generalizations.