Researchers at New York University engineered tiny spheres that self-assemble to form massive, ever-changing flocks. All it took was some chemistry, some physics, and the flip of a light switch.

Leave these special little spheres alone in their solution and they jiggle randomly. Flip on a UV light switch and they suddenly self-assemble into tiny little flocks, with occasional absconders that will immediately jet to other flocks. What's causing this?

The tiny particles are polymers covering hematite, an iron oxide. They don't entirely enclose the hematite, meaning little bits of it are exposed. Although magnetism plays a small part of the flocking, the researchers, whose goal was to make nonliving things imitate living behavior, say the key is the solution in which the particles are suspended. It's hydrogen peroxide, and when exposed to light, it breaks down into water and oxygen. This chemical change transfers energy to the balls and lets them briefly swarm to each other. Then the light goes off and they go back to aimless jiggling.

Top Image: Donald Macauley

Read more at Physics Central or at Science, AAAS.