Regularizations of time-crystal dynamics.

We demonstrate that nonconvex Lagrangians, as contemplated in the theory of time crystals, can arise in the effective description of conventional, physically realizable systems. Such embeddings resolve dynamical singularities which arise in the reduced description. Microstructure featuring intervals of fixed velocity interrupted by quick resets-"Sisyphus dynamics"-is a generic consequence. In quantum mechanics, this microstructure can be blurred, leaving entirely regular behavior.