BIRDS of a feather flock together and now so can brainless, inanimate blobs. These artificial swarms could shed light on the mechanisms behind the natural variety.
The extent to which individual intelligence or underlying physical laws drive birds, fish and other organisms to swarm is still mysterious. To investigate, Jérémie Palacci of New York University and his colleagues created plastic micro-spheres, each with a cubic patch of haematite, an iron oxide, on its surface, then dropped them into the liquid hydrogen peroxide.
Shining blue light on the particles caused the haematite cubes to catalyse the breakdown of nearby hydrogen peroxide into water and oxygen. Osmotic forces then drove more hydrogen peroxide into these regions, buffeting the spheres. But when two spheres came close enough to each other, the balance of chemical forces shifted so that the two were attracted. With enough spheres in the same place, they clustered to form symmetrical arrangements, which the team dubbed “living crystals” (see video, bit.ly/WXNkqm).
These crystals continue to be buffeted by the breakdown of hydrogen peroxide – but they move together as one object, replicating a life-like swarm (Science, doi.org/kc5). “Even though the particles have no social interaction or intelligence, they can exhibit collective behaviour,” Palacci notes.
This article appeared in print under the headline “Brainless blobs can become swarm-mongers too”