What happens to matter as it approaches the coldest possible temperature in the universe—absolute zero? At this extreme limit, where motion nearly comes to a standstill, the rules of physics transform in bizarre and unexpected ways. Absolute zero is the theoretical point, 0 Kelvin, at which all thermal energy is removed and atoms no longer jiggle with heat. But instead of simply freezing solid, strange things happen: particles lose their individuality and collapse into a single quantum state, matter can become a superfluid that flows without resistance, and entire collections of atoms behave like one giant “super-atom.” This is the bizarre frontier of physics, where the familiar laws of nature give way to the strange world of quantum mechanics, and where scientists are still uncovering mysteries that challenge our understanding of reality itself.