THE PHYSICS OF FLOCKING. Studying one of the more remarkable examples of collective behavior, scientists at IBM and the University of Oregon have developed a physics- based theory of how a group of birds manages to move together as a single unit, even if the individual birds make frequent misjudgments and can only see an extremely small fraction of the other birds in the flock. In their model, the researchers capitalized on similarities between certain features of flock motion and several phenomena in physics. Like a group of tiny bar magnets, the birds in the flocking model line themselves up in the same direction by interacting with their closest neighbors. Like dust particles in a fluid, nearby birds may soon find themselves far apart. Like parcels of hot material spreading their heat through the process of convection, birds spread information about the direction which they are moving by circulating themselves through the flock. By incorporating the well-developed mathematical descriptions of these processes in the model, and plugging in typical values of such parameters as how fast real flocks move in the air, Tu and Toner came up with realistic predictions of such things as how densely the birds are packed together in certain situations and how this density fluctuates. (John Toner and Yuhai Tu, Physical Review E, October 1998; more at www.aip.org/physnews/preview)