The Physics of human behaviour

What does this mean for the adoption of a new economics and complementary currencies?

FADS, fashions and dramatic shifts in public opinion all appear to follow a physical law: one of the laws of magnetism.

Quentin Michard of the School of Industrial Physics and Chemistry in Paris and Jean-Philippe? Bouchaud of the Atomic Energy Commission in Saclay, France, were trying to explain three social trends: plummeting European birth rates in the late 20th century, the rapid adoption of cellphones in Europe in the 1990s and the way people clapping at a concert suddenly stop doing so. In each case, they theorised, individuals not only have their own preferences, but also tend to imitate others.

"Imitation is deeply rooted in biology as a survival strategy," says Bouchaud. In particular, people frequently copy others who they think know something they don't.

To model the consequences of imitation, the researchers turned to the physics of magnets. An applied magnetic field will coerce the spins of atoms in a magnetic material to point in a certain direction. And often an atom's spin direction pushes the spins of neighbouring atoms to point in a similar direction. And even if an applied field changes direction slowly, the spins sometimes flip all together and quite abruptly.

The physicists modified the model such that the atoms represented people and the direction of the spin indicated a person's behaviour, and used it to predict shifts in public opinion.

In the case of cellphones, for example, it is clear that as more people realised how useful they were, and as their price dropped, more people would buy them. But how quickly the trend took off depended on how strongly people influenced each other. The magnetic model predicts that when people have a strong tendency to imitate others, shifts in behaviour will be faster, and there may even be discontinuous jumps, with many people adopting cellphones virtually overnight.

More specifically, the model suggests that the rate of opinion change accelerates in a mathematically predictable way, with ever greater numbers of people changing their minds as the population nears the point of maximum change. Michard and Bouchaud checked this prediction against their model and found that the trends in birth rates and cellphone usage in European nations conformed quite accurately to this pattern. The same was true of the rate at which clapping died away in concerts.

(From issue 2498 of New Scientist magazine, 06 May 2005, page 15)