The Clockwork Universe by Edward Dolnick Page B

different laws. Heaven and Earth completely differ from one another. The stars are gleaming dots of light moving across the sky, the Earth a colossal rock solid and immobile at the center of the universe. The heavens are predictable, the Earth anything but. On June 1, to pick a date at random, we know what the stars in the night sky will look like, and we know that they will look virtually the same again on June 1 next year, and next century, and next millennium. 21 What June 1 will bring on Earth this year, or any year, no one knows.
    Aristotle had explained how it all works, both in the heavens and on Earth, about three hundred years before the birth of Christ. For nearly two thousand years everyone found his scheme satisfactory. All earthly objects were formed from earth, air, fire, and water. The heavens were composed of a fifth element or essence, the quintessence , a pure, eternal substance, and it was only in that perfect, heavenly domain that mathematical law prevailed. Why do everyday, earthly objects move? Because everything has a home where it belongs and where it returns at the first opportunity. Rocks and other heavy objects belong down on the ground, flames up in the air, and so on. A “violent” motion—flinging a javelin into the air—might temporarily overcome a “natural” one—the javelin’s impulse to fall to the ground—but matters quickly sort them selves out.
    The picture made sense of countless everyday observations: Hold a candle upright or turn it downward, and the flame rises regardless. Hoist a rock overhead in one hand and a pebble in the other, and the rock is harder to hold aloft. Why? Because it is bigger and therefore more earth-y, more eager to return to its natural home.
    All such explanations smacked of biology, and to modern ears the classical world sounds strangely permeated with will and desire. Why do falling objects accelerate? “The falling body moved more jubilantly every moment because it found itself nearer home,” writes one historian of science, as if a rock were a horse returning to the barn at the end of the day.
    The new scientists would strip away all talk of “purpose.” In the new way of thinking, rocks don’t want to go anywhere; they just fall. The universe has no goals. But even today, though we have had centuries to adapt to the new ideas, the old views still exert a hold. We cannot help attributing goals and purposes to lifeless nature, and we endlessly anthropomorphize. “Nature abhors a vacuum,” we say, and “water seeks its own level.” On a cold morning we talk about the car starting “reluctantly” and then “dying,” and if it just won’t start we pound the dashboard in frustration and mutter, “Don’t do this to me.”
    It was Galileo more than any other single figure who finally did away with Aristotle. Galileo’s great coup was to show that for once the Greeks had been too cautious. Not only were the heavens built according to a mathematical plan, but so was the ordinary, earthly realm. The path of an arrow shot from a bow could be predicted as accurately as the timing of an eclipse of the sun.
    This was a twofold revolution. First, the kingdom of mathematics suddenly claimed a vast new territory for itself. Second, all those parts of the world that could not be described mathematically were pushed aside as not quite worthy of study. Galileo made sure that no one missed the news. Nature is “a book written in mathematical characters,” he insisted, and anything that could not be framed in the language of equations was “nothing but a name. ” 22
    Aristotle had discussed motion, too, but not in a mathematical way. Motion referred not only to change in position, which can easily be reduced to number, but to every sort of change—a ship sailing, a piece of iron rusting, a man growing old, a fallen tree decaying. Motion, Aristotle decreed