Bristlebots assemble The "arena" used to study how bristlebots encased in rings and foil interact with each other. An unmodified blue bristlebot is also shown. (Courtesy: Horst-Holger Boltz)"> Bristlebots assemble The "arena" used to study how bristlebots encased in rings and foil interact with each other. An unmodified blue bristlebot is also shown. (Courtesy: Horst-Holger Boltz)

Flocks of birds, schools of fish, colonies of swimming bacteria and even crowds of humans have something important in common. Although the details of how they move and interact are very different, they are all examples of what physicists call “active matter” – collections of particles that propel themselves through their environments, consuming energy as they go.

Because real-world active matter systems can be complex and hard to model mathematically, physicists working in this field sometimes study simpler “toy” systems instead.…