Clock Mystery Solved: 300-Year-Old Pendulum Puzzle Pieced Together by Scientists

Scientists may have solved a 300-year-old mystery. They've found out what causes pendulum clocks to sync up over time.

In 1665, the inventor of the pendulum clock, Christiaan Huygens, noticed that two of his clocks actually synced up over time; no matter how the pendulums on the clocks began, within about half an hour, the pendulums ended up swinging in exactly the opposite direction from each other. This effect, called Huygens synchronization, has remained unexplained-until now.

In this case, researchers argue that tiny pulses created by ticking clocks travel through the wood connecting them and slowly pushed the pendulums into their synchronized swing.

The scientists actually recreated the old experiment with two clocks of their own attached to an aluminum beam. They started the clocks to ticking and measured each swing of their pendulums with high-precision sensors. Over several hours, the swings came into sync with one another.

"We assume that the coupling is obtained through the exchange of sound pulses between the clock propagated through the rail," write the researchers in their paper. "When one clock receives the kick, the impact propagates in the wall slightly perturbing the second clock. In this model each clock transmits once per cycle a sound pulse that is translated in a pendulum speed change."

The new findings don't just solve a 300-year-old mystery, though. The researchers also hope to expand their model to explain the behavior of other kinds of oscillators, such as the electronic oscillators used to synchronize activity on microchips.

"The exact mechanism of how the pulse energy propagates through the clock hardware down to the pendulum is hard to assess in detail and depends on the individual clock," said Luis Melo, one of the researchers, in an interview with Smithsonian Magazine.

The findings are published in the journal Scientific Reports.

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