Physicists at New York University have developed a new type of time crystal using sound waves to suspend tiny styrofoam beads, resulting in nonreciprocal interactions that defy Newton's third law of motion. The compact, visible system oscillates in a steady rhythm and was detailed in Physical Review Letters. Researchers suggest potential applications in quantum computing and insights into biological rhythms.
Time crystals, first theorized and confirmed about a decade ago, consist of particles that exhibit periodic motion without external energy input. The latest version, created by a team at New York University's Center for Soft Matter Research, employs an acoustic levitator to keep small styrofoam beads afloat mid-air using standing sound waves. These beads interact via scattered sound waves, producing uneven forces: larger beads influence smaller ones more strongly than vice versa, violating the equal-and-opposite reaction principle of Newton's third law. This leads to spontaneous oscillations, forming the time crystal's rhythmic pattern. The setup is simple—a handheld device about one foot tall—making it observable without specialized equipment. Lead author Mia C. Morrell, a graduate student, explained: 'Sound waves exert forces on particles—just like waves on the surface of a pond can exert forces on a floating leaf. We can levitate objects against gravity by immersing them in a sound field called a standing wave.' She likened the interactions to 'two ferries of different sizes approaching a dock,' where size differences cause asymmetric wave effects. Senior author David G. Grier, a physics professor, noted: 'Time crystals are fascinating not only because of the possibilities, but also because they seem so exotic and complicated. Our system is remarkable because it's incredibly simple.' Collaborator Leela Elliott, an undergraduate, contributed to the work published in Physical Review Letters (2026; 136(5), DOI: 10.1103/zjzk-t81n). The National Science Foundation supported the research via grants DMR-21043837 and DMR-2428983. Beyond technology like quantum computing, the nonreciprocal dynamics mirror processes in circadian rhythms and food metabolism.
