Tokyo University of Science researchers observe particles defying Newton's third law

Researchers at the Tokyo University of Science have documented a large-scale colloidal system of over 10,000 microscopic particles that defies Newton’s third law of motion. By breaking the traditional action-reaction symmetry, the particles exhibit non-reciprocal interactions that allow for spontaneous, autonomous movement.

Led by Professors Yutaka Sumino and Kiwamu Yoshii, the study utilized polystyrene colloidal particles of varying sizes suspended in water. When subjected to an alternating electric field, electrohydrodynamic flows were created. Because the strength of these flows depended on particle size, larger particles exerted a stronger attraction on smaller ones than they received in return. This imbalance caused particles to form asymmetric pairs and larger clusters that act as self-propelled units.

This discovery in non-reciprocal many-body physics presents new challenges for computational modeling. Simulating these non-equilibrium systems requires significant high-performance computing resources, as the asymmetric coupling terms demand complex matrix calculations that exceed the capabilities of standard CPU architectures.