Physicists have successfully challenged a cornerstone of classical mechanics. A team based at the Tokyo University of Science recently observed 10,000 colloidal particles defying Newton’s third law of motion for an hour. This law, which dictates that every action must have an equal and opposite reaction, serves as a foundation for understanding how objects interact in our daily environment. By breaking this symmetry, the researchers opened a new way to observe collective movement.
The experiment involved suspending particles of varying sizes in water. The team applied an alternating electric field to the mixture. This field forced the particles into a state where they formed pairs and began chasing one another through the liquid. Unlike a standard system where particles might simply clump together into a crystal, these units remained separate and mobile. They moved as self-propelled entities rather than settling into a static state.
Yutaka Sumino, a co-author of the study, notes that this break in symmetry is a driver for new types of collective motion and self-organization. When particles of only one size were tested, they acted as expected and formed a crystal. The unique behavior appeared only when the team introduced the size imbalance and the electric field. This suggests that the environment and the physical composition of the particles are both necessary for this reaction.
The implications for this study extend into biological research. The team believes this mechanism may mirror how cell colonies or groups of animals function in nature. Understanding how these particles move without relying on traditional action-reaction symmetry could lead to the development of new programmable materials or specialized microrobotic systems. By observing these 10,000 particles, researchers now have a clearer window into the mechanics of self-organizing matter.