Tiny particles defy action-reaction symmetry to stay in motion
From schools of fish and flocks of birds to microscopic synthetic particles, many systems in nature and the laboratory consist of individual units or agents that move by consuming energy. These systems are known as active matter because their components continuously use energy to generate motion, either individually or through interactions with their environment.
Tiny synthetic particles have been observed to defy the traditional action-reaction symmetry in motion, defying Newton's third law. Researchers at the Tokyo University of Science have discovered that nonreciprocal interactions between particles, in which one particle exerts a stronger influence than it receives, can lead to collective motion and self-organization.
By creating a colloidal system with particles of different sizes in an alternating electric field, the team was able to generate asymmetric electrohydrodynamic (EHD) flows that caused larger particles to attract smaller ones more strongly than vice versa. This created asymmetric, self-propelled structures that moved through the suspension despite individual particles being incapable of propulsion.
The resulting clusters repeatedly fragmented, rearranged, and reformed, demonstrating that nonreciprocal interactions can fundamentally alter conventional collective dynamics. The study's findings suggest that similar mechanisms could be at play in biological systems, inspiring future research into programmable materials and microrobotic systems.
Written by urgent.news from Phys.org's reporting — not their text. Machine-written — it may contain errors, so check the original before relying on it.
