Birds flock, bees swarm and fish school. These are just some of the
remarkable examples of collective behavior found in nature. Physicists
have been able to capture some of this behavior by modeling organisms as
tiny arrows that align with their neighbors according to simple rules.
Successes like these have spawned a field devoted to the physics of
.active matter,. which studies both living and non-living systems where
a large number of individually driven units exhibit coherent
organization at larger scales. Such systems include suspensions of
swimming bacteria, layers of migrating cells, and collections of
synthetic microswimmers. Physicists, biologists, engineers and
mathematicians are now engaged in modeling the complex behavior of these
systems, and in trying to identify universal principles.