Discrete time crystals in the absence of manifest symmetries or disorder in open quantum systems.

We establish a link between metastability and a discrete time-crystalline phase in a periodically driven open quantum system. The mechanism we highlight requires neither the system to display any microscopic symmetry nor the presence of disorder, but relies instead on the emergence of a metastable regime. We investigate this in detail in an open quantum spin system, which is a canonical model for the exploration of collective phenomena in strongly interacting dissipative Rydberg gases. Here, a semi-classical approach reveals the emergence of a robust discrete time-crystalline phase in the thermodynamic limit in which metastability, dissipation, and inter-particle interactions play a crucial role. We perform large-scale numerical simulations in order to investigate the dependence on the range of interactions, from all-to-all to short ranged, and the scaling with system size of the lifetime of the time crystal.