# Mathematical Digest

### Short Summaries of Articles about Mathematics

in the Popular Press

"Animal Magnetism: Why, mathematically, birds of a feather flock together," byRobert J. Coontz, Jr. *The Sciences*, May/June 1996, pages 10-11.

A magnet is a system of interacting components, all of whose quantum mechanicalspins point in the same direction. Although each component only "knows" thespin of its nearest neighbors, the short-range interactions nevertheless giverise to a long-range phenomenon, that of magnetization of the entire system.Renormalization theory, developed in the 1970s by physics Nobelist KennethG. Wilson, attempts to explain mathematically how such things can occur. Thisarticle discusses attempts to use renormalization theory to model how birds flyin flocks. Each bird knows only the direction in which others nearest to itare traveling, and yet the entire flock travels in the same direction. As thearticle explains, the motion of the flock is important in insuring that thebirds stay in formation and all fly in the same direction.performances.

*-Allyn Jackson*