Watch these metronomes spontaneously synchronize

Five metronomes started at different times eventually synchronize in this nifty video from UCLA. It's been a known phenomenon since the 17th century:

In 1665, Dutch physicist Christiaan Huygens, inventor of the pendulum clock, was lying in bed with a minor illness and watching two of his clocks hanging on a wall, said Henrique Oliveira, a mathematician at the University of Lisbon and co-author of a new study detailing the findings.