Pendulum clocks have an air of majesty to them, a mesmerizing lull, a kind of antique magic. Until the 1930s, they were the world's most accurate form of timekeeping technology. And even though they've become outmoded today, the gentle tick-tock of a pendulum clock still has the power to enchant.

Ever since pendulum clocks were first invented in 1656 by Christiaan Huygens, the technology has also been at the heart of a great physics mystery. Huygens himself observed that whenever two or more pendulum clocks were hung on the same wall together, they slowly but surely came to synchronize their swings.

How and why this happens has remained a scientific puzzle over the centuries. A number of theories have been tried and tested, but there has been no consensus.

That is, until now. A pair of Portuguese scientists now believe they have solved the mystery, reports the Guardian. In a study published in the journal Scientific Reports, the scientists claim that pendulums synchronize due to sound pulses in the air.

“We could verify that the energy transfer is through a sound pulse,” said co-author Luis Melo, from Lisbon University’s physics department.

The pair reached their conclusion after developing a complex mathematical model for their hypothesis. They then conducted experiments to see whether the mathematical model accurately described the synchronization of two real, swinging pendulum clocks. Their theoretical predictions matched the real-life phenomenon perfectly.

It's a fascinating solution, one which finally solves a nearly 350-year conundrum.

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Why do pendulum clocks swing together?
Pendulum clocks hanging on the same wall will synchronize their swings over time, and now scientists finally know why.