In the 17th century, Christiaan Huygens, inventor of the pendulum clock, noticed a curious phenomenon. When two identical pendulum clocks are mounted next to each other on a wall, their swings ...

Timekeeping can be as simple as counting "one Mississippi, two Mississippi . . ." prior to blitzing in backyard football, or tracking the back-and-forth swings of a pendulum in a grandfather clock. In ...