Pendulum

Park Kyung-ryul

The author is a professor at the KAIST Graduate School of Science and Technology Policy.

Watching the pendulum of a wall clock brings a curious sense of reassurance. Perhaps it comes from the belief that however far it swings, it will eventually return to the center.

A pendulum’s motion is an honest exchange of potential and kinetic energy. It descends carrying all the energy stored as it rises, then climbs just as high on the opposite side. In 1583, at Pisa Cathedral, 19-year-old Galileo is said to have measured the period of a swinging ceiling lamp against his pulse. Whether the swing was wide or narrow, each round trip seemed to take the same time. This is the isochronism of the pendulum, which later became the basis of the pendulum clock.

But there is a condition. It holds only when the angle of motion is small. As the amplitude increases, the period grows longer.

In a pendulum swinging violently, I see our society. The farther it travels toward one side, the farther it swings toward the opposite extreme. Extremism on one side invariably becomes the justification for extremism on the other, making the next swing wider. Recovery takes longer, and all of us hanging from the pendulum pay the price.

There is also a critical point that must not be crossed. Once the pendulum goes over the top, it loses its balance and spins in one direction. Just as a clock cannot measure time with a pendulum that never returns, a society thrown off its orbit cannot move toward the future.

What, then, can reduce a dangerously widening amplitude? Friction. It is the kind of thing we usually find bothersome, like air resistance or stiffness at the pivot. In society, it means tedious dialogue and compromise, principles that withstand discomfort and tolerance of others. Only by enduring that arduous process, and refusing to lose sight of the center even while swinging, can our social clock recover its proper rhythm.

I look again at the wall clock. Perhaps what Galileo noticed in the lamp was not the swing but the return. The clock’s hands move forward not because the pendulum surges violently to one side, but because it unfailingly descends and passes through its lowest point.

The most powerful force moving the world, too, is not the pull toward opposing extremes, but the steady restoring force that insists on finding the center again. A healthy society does not stop swinging altogether. It keeps moving, but within shared bounds that allow disagreement without destroying the common center.