Image: Gary Meek; Georgia Tech Research Corporation

Physicists at the Georgia Institute of Technology recently re-created--and at last explained--a 335-year-old experiment in the hopes that it will shed light on a modern-day puzzle, synchronized oscillators. Today researchers investigating this phenomena most often examine electrical systems, but Kurt Wiesenfeld and Michael Schatz (reflected in pendulum at right), along with undergraduate student Matthew Bennett, instead turned to a mechanical analogue: they built an exact replica of two pendulum clocks studied by the Dutch astronomer and physicist Christian Huygens in 1665.

Huygens, who described his findings in a letter to his father, found that the two clocks would repeatedly return to a synchronized pattern regardless of how they were started, stopped or otherwise disturbed. In addition, he noted that they only seemed to synchronize such that the two pendulums swung in opposite directions (anti-phase), never in the same direction (in-phase). Huygens, working 20 years before Sir Isaac Newton formulated the laws of mechanics, guessed that the swinging somehow "imperceptibly" moved the platforms to which the clocks were attached.

The new experiment, monitored by lasers, showed that he was for the most part right. "A key feature of our understanding of Huygens's clocks is that the in-phase motion doesn't couple to the platform in the same way as the anti-phase motion," Schatz says. "In-phase motion can drive the very small platform movement." Anti-phase motion, on the other hand, balances the swinging of the pendulums. Adds Wiesenfeld, "Classical physics still has things to teach us." (For more on Wiesenfeld's work, see his article, THE BENEFITS OF BACKGROUND NOISE, co-authored with Frank Moss in the August 1995 issue of Scientific American.)