From swarming bacteria to tissue cells, living matter defies classic physical models of motion

A new study published in Nature Physics challenges traditional physical models by demonstrating that living matter, such as bacteria and human respiratory cells, defies the classic principles of symmetry. Researchers from Ben-Gurion University of the Negev, Bar-Ilan University, and the University of Geneva found that these self-propelled cells spontaneously break mirror symmetry, moving in curved, irreversible spiral paths.

In nature, collections of rod-shaped objects like bacteria and cells form an "active nematic" state, where they spontaneously create topological defects that constantly form in pairs and cancel each other out. However, the researchers discovered that living systems break these established expectations, with defect pairs following co-rotating spiral trajectories instead of straight, mirrored lines.

This finding, published in Nature Physics, introduces a new physical framework for understanding how living communities self-organize.