Isaac Newton by James Gleick

Author:James Gleick [Gleick, James]
Format: epub, azw3, mobi
ISBN: 978-0-307-42643-7
Publisher: Knopf Doubleday Publishing Group
Published: 2012-06-12T16:00:00+00:00

One flash of inspiration had not brought Newton here. The path to universal gravitation had led through a sequence of claims, each stranger than the last. A force draws bodies toward the center of the earth. This force extends all the way to the moon, pulling the moon exactly as it pulls an apple. An identical force—but toward the center of the sun—keeps the earth in orbit. Planets each have their own gravity; Jupiter is to its satellites as the sun is to the planets. And they all attract one another, in proportion to their mass. As the earth pulls the moon, the moon pulls back, adding its gravity to the sun’s, sweeping the oceans around the globe in a daily flood. The force points toward the centers of bodies, not because of anything special in the centers, but as a mathematical consequence of this final claim: that every particle of matter in the universe attracts every other particle. From this generalization all the rest followed. Gravity is universal.

Newton worked out measurements for weights on the different planets. He calculated the densities of the planets, suggesting that the earth was four times denser than either Jupiter or the sun. He proposed that the planets had been set at different distances so that they might enjoy more or less of the sun’s heat; if the earth were as distant as Saturn, he said, our water would freeze.25

He calculated the shape of the earth—not an exact sphere, but oblate, bulging at the equator because of its rotation. He calculated that a given mass would weigh differently at different altitudes; indeed, “our fellow countryman Halley, sailing in about the year 1677 to the island of St. Helena, found that his pendulum clock went more slowly there than in London, but he did not record the difference.”26

He explained the slow precession of the earth’s rotation axis, the third and most mysterious of its known motions. Like a top slightly off balance, the earth changes the orientation of its axis against the background of the stars, by about one degree every seventy-two years. No one had even guessed at a reason before. Newton computed the precession as the complex result of the gravitational pull of the sun and moon on the earth’s equatorial bulge.

Into this tapestry he wove a theory of comets. If gravity was truly universal, it must apply to these seemingly random visitors as well. They behaved as distant, eccentric satellites of the sun, orbiting in elongated ellipses, crossing the plane of the planets, or even ellipses extended to infinity—parabolas and hyperbolas, in which case the comet never would return.

These elements meshed and turned together like the parts of a machine, the work of a perfect mechanic, like an intricate clock, a metaphor that occurred to many as news of the Principia spread. Yet Newton himself never succumbed to this fantasy of pure order and perfect determinism. Continuing to calculate where calculation was impossible, he saw ahead to the chaos that could emerge in the interactions of many bodies, rather than just two or three.

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