Men who let their beards grow, a collective social phenomenon to which British Prince William has fallen prey.

The Internet bubble, high interest rates for Italy, funny cat videos on YouTube, and the unexpected renewed popularity of beards: you can call them fads, hypes or memes, but Diego Garlaschelli, from the Lorentz Institute for Theoretical Physics, prefers the term ‘collective social phenomena’.

Garlaschelli’s econophysics research group focuses on complex systems outside the realm of traditional physics. ‘The models and theories of physics often also apply to complex systems in economics, biology and social sciences,’ says Garlaschelli. Take, for instance, the way in which opinions spread through networks of social contacts like a virus: it simply demands a scientific interpretation.

Dr Diego Garlaschelli

Funnily enough, this model leads to a paradox. ‘If people keep exchanging their views in new ways, as is happening now via Internet, you would expect that the diversity of opinions would decrease,’ Garlaschelli explains. In practice, the opposite seems to be happening: the point at which everyone wholeheartedly agrees with each other now appears more remote than ever.

The paradox emerges even more clearly in a computerised version of the model, which generates thousands of virtual people with randomised views who subsequently influence each other through a network of social contacts.

Another collective social phenomenon: silver-grey is the world's favourite colour for cars, including in the Netherlands.

Garlaschelli and his colleagues draw attention to this flaw in the academic journal PNAS by not using randomly generated initial values, as it is customary to do in computer models. The model does in fact prove to be effective when using realistic data taken from the Eurobarometer, a study of opinion among nearly thirteen thousand Europeans about all kinds of subjects, from nuclear energy to tourism.