Physicists at New York University have revealed a new kind of time crystal — an unusual form of matter whose particles perform stable rhythmic motion. In this new system, particles are visible without special instruments and are held in mid‑air by sound waves, reported in Physical Review Letters.
Unlike earlier interpretations, this setup works in the macroscopic world, can be seen with the naked eye, and particles interact by exchanging sound waves, seemingly breaking familiar motion rules. Time crystals are systems whose particles move in repetitive cycles without external influence; their existence was first theorized and later confirmed experimentally about a decade ago.
In the study, researchers used acoustic levitation: small styrofoam beads were held in place by a standing sound wave and interacted with each other by sound vibrations.
“Sound waves act on particles like waves on water affect a floating leaf,” explains graduate student Mia Morrell.
According to her, placing particles in a field of standing waves allows them to be held against gravity, and their interaction is unusual — larger beads influence smaller ones more strongly, creating non‑symmetric interactions.
This behavior appears to defy Newton’s Third Law (equal and opposite forces), because the forces between particles are unbalanced, enabling self‑sustained oscillations — the essence of a time crystal.
Lead researcher, physics professor David Grier, highlighted the simplicity of the system:
“Although time crystals seem exotic and complex, our system is remarkable for its incredible simplicity,” he says.
