Last modified: Thursday, April 29, 2004
From Galileo's pendulum to the Global Positioning System
BLOOMINGTON, Ind. -- Galileo was bored.
As he listened to a Mass in the drafty cathedral of Pisa in 1581, the 17-year-old student noticed something interesting. A chandelier high overhead was swaying in the breeze, sometimes barely moving and other times swinging in a wide arc. His curiosity aroused, he timed the swings with his pulse. To his surprise, it took the same number of pulse beats for the chandelier to complete one swing no matter how far it moved. The wider the swing, the faster the motion, but always in the same amount of time. So time could be measured by the swing of a pendulum -- the basis for the pendulum clock.
The story of what Galileo's observation meant, and its profound consequences for modern science and technology, are described in a new book, Galileo's Pendulum (Harvard University Press), by Indiana University Bloomington physicist Roger Newton.
"The legend of how Galileo discovered this property of the simple pendulum is apocryphal, but neither the fact that he found it nor the profound effects that it had on our civilization can be denied," Newton said.
"The physics of the harmonic oscillator -- that is, Galileo's pendulum -- leads far beyond a mere device for making accurate clocks," he said. "These oscillators have been found to be the basis not only of what we hear as the sound of music and see as the colors of light but, via the quantum theory, of what we understand as the fabric of the universe. Without oscillators, there would be no particles -- no air to breathe, no fluids to sustain life and no solid matter to form the Earth. This book is the story of the simplest but most fundamental physical system in nature and how it ties the rhythm of time together with our very existence."
Galileo's realization about the pendulum came at a favorable time. After the Renaissance, there were urgent commercial pressures to find a way to measure time more accurately so that navigation at sea could be improved.
"After many shipwrecks caused by errors in estimating a ship's location, the British government offered a substantial prize for a clock that would be reliable at sea," Newton explained. With such a clock, sailors could measure their longitude by using the clock to keep track of the time in London, for example, and then determining their local time by the sun. The difference between the two times would tell them how far they were east or west of London. They could measure their latitude from the sun as well, and the combination would let them plot their location anywhere on the globe.
Many refinements of the pendulum clock were needed to allow for the pitching and rolling of a ship at sea, especially during a storm, but eventually the problem was solved and the prize was awarded. All of the clocks involved relied on Galileo's discovery.
The descendant of those efforts is the modern Global Positioning System, which uses precise clocks in orbiting satellites to determine a particular location on the ground below. Using GPS, a person can tell within a few feet where he or she is on the planet.
From Galileo's pendulum to the Global Positioning System is a long journey indeed, but the steady motion of the swaying chandelier can still be detected at every stage. From the reliable clocks that brought order to the rhythms of everyday life, to the behavior of electrons and other particles, the underlying principle is the same.
"Little could Galileo have realized," Newton concluded, "that the harmonic oscillator, whose isochronism he discovered in his youth, would turn out to be the most basic, all-pervading physical system in the world and a crucial building block for our understanding of nature."