300-Year-Old Mystery Finally Solved

300-Year-Old Mystery Finally Solved

Scientists have finally tackled the centuries-old mystery of why two pendulum clocks put side by side are automatically synchronized. Their explanation: sound pulses.

In 1665, the Dutch physicist Christiaan Huygens observed a strange fact: the motion of two pendulum clocks hanging on the same wall is synchronous. Whatever their starting position, the clocks get in phase opposition: a pendulum goes left while the other goes right.

Since then, the mystery has remained. But now, researchers at the University of Lisbon (Portugal) suggest an explanation, published Thursday in Scientific Reports of the journal Nature.

The sound pulses - a sound wave carrying energy - can move from one clock to another, causing them to synchronize.

The researchers confirmed their theoretical model with two pendulum clocks attached to an aluminum rail mounted on a wall. Result: The change of the motion speed of the pendulums is related to the production of sound pulses.

"Apart from the resolution of an old mystery, this discovery opens the way to understanding other types of oscillators (for example electronic)," said Lu?s V. Melo, co-author of the study.