Perpetual motion machines are impossible, at least in our everyday world. But down at the level of quantum mechanics, the laws of thermodynamics don’t always apply in quite the same way. In 2021, after years of effort, physicists successfully demonstrated the reality of a “time crystal,” a new state of matter that is both stable and ever-changing without any input of energy. In this episode, Steven Strogatz discusses time crystals and their significance with the theoretical physicist Vedika Khemani of Stanford University, who co-discovered that they were possible and then helped to create one on a quantum computing platform.