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.