chapter 1 Galileo The Way Things Really Move Galileo Galilei, by Ottavio Leoni It is very unpleasant and annoying to see men, who claim to be peers of anyone in a certain field of study, take for granted certain conclusions which later are quickly and easily shown by another to be false. --Salviati, in Galileo, Two New Sciences W hen you throw a rock, catch a ball, or jump just hard enough to clear a hurdle, the older, unconscious part of the brain, the cerebellum, reveals an effortless grasp of the fundamental laws of motion. Force equals mass times acceleration. Every action results in an equal and opposite reaction. But this ingrained physics is sealed off from the newer, upper brain-the cerebrum, seat of intelligence and self-awareness. One can leap as gracefully as a cat but be just as powerless to explain the inverse square law of gravity. Aristotle, in the fourth century BC, made the first ambitious attempt to articulate the rules of motion. An object falls in proportion to its weight-the heavier a rock, the sooner it will reach the ground. For other kinds of movement (pushing a book across a table or a plow across a field), a force must be constantly applied. The harder you push, the faster the object will go. Stop pushing and it will come to a halt. It all sounds eminently sensible and obvious and, of course, is exactly wrong. What if you place the book on a sheet of ice and give it a gentle shove? It will keep moving long after the impetus is removed. (Asked why an arrow keeps going after it leaves the bowstring, the Aristotelians said that it was pushed along by the incoming rush of air.) Now we know that something set in motion stays in motion until stopped by something else, or worn down by friction. And a one-pound weight and a five-pound weight, dropped at the same moment, will fall side by side to the ground. Galileo showed it was so. It's entirely predictable that the great debunker of Aristotle-celebrated in a play by Bertolt Brecht, an opera by Philip Glass, and a pop song by the Indigo Girls-would come in for his own debunking. It is doubtful, historians tell us, that Galileo dropped two weights from the Leaning Tower of Pisa. Nor do they believe that he hit on his insight about pendulums-that each swing is of equal duration-while watching a certain chandelier in the cathedral of Pisa and timing it with his heartbeat. His credentials as a cosmologist have also dimmed under scrutiny. Galileo was the most eloquent advocate of Copernicus's sun-centered solar system-his Dialogue Concerning the Two Chief World Systems is the first great piece of popular science writing-but he never accepted Kepler's crucial insight: that the planets move in ellipses. The orbits, Galileo assumed, had to be perfect circles. Here he was following Aristotle, who proclaimed that while motion on Earth (in the "sublunar" realm) must have a beginning and an end, celestial motion is necessarily circular. For that to be true and match what was happening in the sky, the planets would have to move not just in circles but in circles within circles-the same old epicycles that had weighed down Ptolemy's geocentric universe. Galileo brushed off the problem. Most disappointing of all, he probably did not, as legend has it, follow his forced apology to the Inquisitors of Rome by muttering under his breath, Eppur si muove, "And yet it moves." He was no martyr. Knowing he had been beaten, he retired to the solitude of Arcetri to lick his wounds. Galileo's strongest claim to greatness lies in work he did long before his troubles with the Vatican. He was studying nothing so grand as stars or planets but the movement of simple, mundane objects-a subject far more perplexing than anyone had imagined. Whether or not the research actually began at the Tower of Pisa hardly matters. He described a similar experiment in Excerpted from The Ten Most Beautiful Experiments by George Johnson, George Johnson All rights reserved by the original copyright owners. Excerpts are provided for display purposes only and may not be reproduced, reprinted or distributed without the written permission of the publisher.
