Bacteria in a drop of water jostle and swim: each on its own, but together they create patterns. With weak motion, the fluid churns like soup on a high flame: vortices collide, and the flow direction changes every second. This is called bacterial turbulence.

But when particles start moving faster, the picture changes. A turbulent flock emerges: chaotic vortices don't disappear, but a global direction of motion appears on top of them. It's like a rush-hour crowd that simultaneously jostles with elbows and moves toward the exit.

The authors found a simple mathematical description that predicts this regime and explains why, as activity increases, the system transitions from complete chaos to order with vortices.