Metronomes, people and starlings

The essence of a complex system is the interaction between its component parts. The fascination of a complex system is that apparently simple interactions can produce unexpected behaviours. Here are three examples featuring, in turn, metronomes, people and starlings.

When several metronomes are set up on a single moveable surface, such as a board on two rollers, and when they are set in out-of-phase motion, they will gradually synchronise with each other. This process is called entrainment. The scientific explanation is that the metronomes interact with each other through small vibrations in the moveable surface.

The Nobel prize-winning economist Thomas Schelling asked himself why racial segregation occurs in human populations. He could equally have asked about segregation based on nationality, caste, religion, ideology or any of the many other ways in which people identify themselves. He carried out an experiment using counters on a chess board and saw that, even with a very mild preference for the colour of a neighbouring counter, the ‘society’ of counters segregated fully into black and white. Even though individuals are rational and fairly tolerant, the societies we produce together may be neither rational nor tolerant.

Flocks of birds and shoals of fish often move in unison to create complex and beautiful patterns without any leadership and without any obvious rationale. For example, scientists have studied the behaviour of murmurations of starlings. Explanations (pdf) (and here) of their collective behaviour suggest that it may help protect the birds from predators.

Watch demonstrations of each of these three phenomena after the jump.


Metronomes



People



Starlings