The Thing with Feathers by Noah Strycker Read Free Book Online Page A

fields, the way that Cavagna applied his understanding of physics to biology.
    “Collective movements are a common phenomenon also in human behaviour,” the project announced. “We think that [it] is worthwhile to explore the possibility of using the models built for the description of flocking, to describe economic herding behaviours. In this way we hope to get new tools to understand the reasons of social events, e.g. fashions, social dominance.” One researcher on the project decided to focus on how people’s friends influenced the music they downloaded and the way that they voted. Cavagna didn’t know much about the mechanics of fashion trends and market bubbles, but he could contribute his knowledge of physics to try to describe, mathematically, how starlings form cohesive groups. His team of physicists and statisticians got down to work analyzing the data they’d collected from the terrace of the Palazzo Massimo.
    They compared the behavior of individual starlings within a flock to the three basic rules used by models dating back to Boids in the 1980s: separation, cohesion, and alignment. Cavagna’s group found that starlings avoid collisions, stay at least a wing’s length away from one another, and seldom stray far enough from one another to break up the flock—just as the models assumed. Starlings also align with one another, but notquite in the way that flocking models traditionally predicted: Instead of basing directional decisions on birds within a certain distance, each starling uses its nearest seven neighbors to decide which direction to fly in, no matter how far away they are.
    This is an important difference. Topological distance—a comparative measurement, like the number of stops on a subway line—appears to be more important than absolute metric distance within a flock. Future models made this adjustment, with good results: When a certain number of nearest neighbors are used instead of those within a certain distance, flocks become less likely to break up, and can expand and contract more easily in response to predators and other fluctuations. And the number seven is particularly interesting. Cavagna mused that even though each starling could probably see more than a dozen individual members of its flock around it, the birds’ brainpower is limited to processing seven at a time.
    This is a trait that humans may share with starlings. In 1956, scientist George Miller published a fascinating paper, “The Magical Number Seven, Plus or Minus Two,” which has become something of a legend; the paper has been cited, at last count, more than 16,000 times in other publications. Miller discussed a variety of experiments that showed an odd psychological convergence on the number seven, not in a black-cat-and-mirrors way, but much more logically.
    He described one experiment where people were presented with a screen on which random patterns of dots were flashed for one-fifth of a second. When fewer than seven dots were shown, people were almost always able to correctly count the dots, but they often resorted to imprecise estimates when more than seven dots were flashed. In another test, a psychologist read aloud lists of random items at a rate of one per second, and then asked people to repeat what they’d just heard. Nomatter what items were being read—words, letters, numbers—people could store about seven unrelated items at a time in their immediate memory, like the seven digits of a phone number. Although these results have been generalized at times past their scientific usefulness—for instance, self-help resources that advise that PowerPoint presentations should have seven main points as a sort of subconscious trick—we do seem to reach certain cognitive limitations near seven items, and starlings may do the same.
    Cavagna’s team wanted to describe starling flocks with pure physics. They measured the velocities of birds at different positions within a flock and found, as you’d expect, that