Apr 06, 2016 I Paul Seaburn

350-Year-Old Pendulum Synchronization Puzzle Finally Solved

The inventor of the pendulum clock gave the world a fine timepiece and a seemingly unsolvable mystery … why do two pendulum clocks positioned closely together on a wall or table end up synchronized in a very short period of time without human intervention. The puzzle has persisted to perplex scientists, clock makers and pendulum clock owners until it was solved recently, and the solution is the same one proposed by the inventor. Why didn’t anyone listen to Christiaan Huygens?

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Christiaan Huygens

In 1665, Huygens, a Dutch physicist, was sick in bed doing what all guys do when they’re sick in bed – complaining and watching the clock. In Huygens’ case, it was two pendulum clocks he had invented. Not sick enough to play, he began messing with the pendulums and found that no matter what position they started in, the two ended up swinging in exactly the opposite direction from each other within 30 minutes.

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An illustration of the pendulum clock invented by Christiaan Huygens

When he felt better, Huygens postulated that the clocks communicated via imperceptible vibrations traveling through the beam they were hanging from. But was unable to prove it – mostly because differential calculus hadn’t been invented yet. Neither was anyone else for 350 years. According to a new study published in Scientific Reports, the puzzle which eventually became known as Huygens’ synchronization has finally been solved and the solution involved going back to Huygen’s sickbed.

Jonatan Peña Ramirez, a dynamicist at the Center for Scientific Research and Higher Education in Ensenada, Mexico, used two identical custom-built monumental (large) pendulum clocks similar to Huygens’ invention. The clocks were placed on a wooden table (Huygens’ were hanging from a wooden beam). The clocks synchronized in a short time but, unlike Hugyens’, they swung in the SAME direction and the clocks slowly and inexplicably lost time.

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The pendulum experiment in action

Having access to differential calculus, Pena developed a mathematical model of the clocks and the flexibility of the wooden table. The model showed that the clocks made the wooden table vibrate enough to synchronize their pendulum swings. Moreover, the rigidity, thickness and mass of the table was responsible for the pendulums swinging in the same direction and the synchronized degradation of the clocks’ accuracy.

Is there a lesson to be learned here? Yes - swinging pendulums or moving rotors in opposite directions is more efficient because their vibrations will cancel each other out and allow them to move or operate without vibration interference, which is why Pena’s same-direction pendulum clocks were less accurate than Huygens’ opposite direction ones.

Also, be a clock watcher when you’re sick.



Paul Seaburn
Paul Seaburn is the editor at Mysterious Universe and its most prolific writer. He’s written for TV shows such as "The Tonight Show", "Politically Incorrect" and an award-winning children’s program. He's been published in “The New York Times" and "Huffington Post” and has co-authored numerous collections of trivia, puzzles and humor. His “What in the World!” podcast is a fun look at the latest weird and paranormal news, strange sports stories and odd trivia. Paul likes to add a bit of humor to each MU post he crafts. After all, the mysterious doesn't always have to be serious.

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