Cryogenics is the scientific study of very low temperatures, and of how to make and use that cold. It is a branch of physics and engineering. People who work in cryogenics learn how gases turn into liquids when they get cold enough, how metals change, and how to keep food, blood, or machine parts at those temperatures. The word looks plural because of the s, but we treat it as a field, like physics or mathematics: Cryogenics is…, not Cryogenics are…. Though actually, everyday English often blurs cryogenics with cryogenic, the adjective, and with cryonics, the hope-and-ice idea about freezing dead bodies. The tidy dictionary keeps them apart: cryogenics is the study; cryogenic describes the tools and the cold; cryonics is the other, more doubtful idea.