To explain the flocking process, the researchers draw parallels between the motion of flocks and several phenomena in physics: namely, the lining up of magnets, the flow of fluids, and the transfer of heat. But the field of "flocking dynamics" didn't begin in the realm of physics. It didn't really begin in the outdoors. It began in the world of microscopic organisms.

Back in 1993, at his laboratory in Budapest, physicist Tamas Vicsek was watching movies of bacteria colonies made by a group of biologists in Germany and his collaborators in Israel. As the bacteria multiplied, he noticed, parts of the colonies of bacillus circulans and a strain of bacillus subtilis formed circles. Looking more closely at the circles, Vicsek saw that the groups of bacteria moved clockwise in half of the circles and counterclockwise in the others. Whether they chose to move clockwise or counterclockwise was completely random, he realized. Because of the lining up of the bacteria Vicsek immediately thought of permanent magnets--similar to those on your refrigerator.

Ferromagnets

A permanent magnet consists of many atoms, each of which acts as if it is a tiny bar magnet with a north and south pole. At room temperature, many of these atoms line up their magnets with those of their neighbors, adding together to create in effect a large bar magnet and giving the overall material a strong ability to attract or repel other magnetic materials.

Permanent magnets, also known as "ferromagnets," depend solely upon the interactions between neighboring atoms. It costs a minimum amount of energy for any two atoms to line up their magnets parallel to each other. These cooperative gestures between neighbors quickly lead to a situation in which many of the magnets in the material are lined up--bringing about magnetism on a large scale.

The Curie Point

But despite their name, "permanent" magnets can lose
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Contact: Ben Stein
bstein@aip.acp.org
(301) 209-3091
American Institute of Physics
25-Sep-1998