New time crystal built using sound waves breaks Newton’s third law

Physicists at New York University have created a new type of time crystal using sound waves, where particles exhibit nonreciprocal motion that appears to violate Newton’s third law of motion, which states that every action has an equal and opposite reaction. In this time crystal, tiny styrofoam beads are acoustically levitated and interact through scattered sound waves, with larger beads exerting a stronger influence on smaller ones than vice versa. This imbalance in forces, enabled by the properties of sound waves, allows the system to break the traditional action-reaction symmetry fundamental to classical physics. Unlike previous time crystals, this new version is visible to the naked eye and operates within a compact device about one foot tall, making it simpler and more accessible for study. The researchers believe this system could provide insights into biological processes like circadian rhythms and nonreciprocal phenomena such as digestion. Their findings, published in Physical Review Letters, open new avenues for understanding complex systems and developing technologies that exploit nonreciprocal