Passion of the Western Mind by Richard Tarnas

Author:Richard Tarnas [Tarnas, Richard]
Language: eng
Format: epub, mobi, pdf
ISBN: 9780307804525
Publisher: Random House, Inc.
Published: 2011-10-19T04:00:00+00:00

The Forging of Newtonian Cosmology

Although Kepler’s mathematical and Galileo’s observational support assured the success of the heliocentric theory in astronomy, the theory still lacked a more encompassing conceptual scheme, a coherent cosmology within which it could fit. Ptolemy had been satisfactorily replaced, but not Aristotle. That the Earth and the other planets moved in elliptical orbits around the Sun seemed clear, but if there were no circling aetheric spheres, then how did the planets, including the Earth, move at all? And what now kept them from flying out of their orbits? If the Earth was moving, thereby destroying the basis of Aristotelian physics, then why did terrestrial objects always fall toward its surface? If the stars were so numerous and distant, then how large was the universe? What was its structure, and where was its center, if any? What happened to the long-recognized celestial-terrestrial division if the Earth was planetary like other heavenly bodies, and if the heavenly bodies now appeared to have Earth-like qualities? And where was God in this cosmos? Until these weighty questions were answered, the Copernican revolution had shattered the old cosmology, but it had not yet forged a new one.

Both Kepler and Galileo had provided vital insights and tools with which to approach these problems. Both had believed and then demonstrated that the universe was organized mathematically, and that scientific progress was achieved by rigorously comparing mathematical hypotheses with empirical observations. And Copernicus’s work had already made the most fertile suggestion for the new cosmology; by making the Earth a planet to explain the Sun’s apparent motion, he implied that the heavens and the Earth should not and could not be considered absolutely distinct. But Kepler went further, and directly applied notions of terrestrial force to celestial phenomena.

The Ptolemaic (and Copernican) circular orbits had always been considered “natural motions” in the Aristotelian sense: by their elemental nature, the aetheric spheres moved in perfect circles, just as the heavy elements of earth and water moved downward and the light elements of air and fire moved upward. Kepler’s ellipses, however, were not circular and constant, but involved the planets in changes of speed and direction at each point in their orbits. Elliptical motion in a heliocentric universe required a new explanation beyond that of natural motion.

Kepler suggested as an alternative the concept of a constantly imposed force. Influenced as always by the Neoplatonic exaltation of the Sun, he believed the Sun to be an active source of movement in the universe. He therefore postulated an anima motrix, a moving force akin to astrological “influences,” which emanated from the Sun and moved the planets—most powerfully close to the Sun, less so when distant. But Kepler still had to explain why the orbits curved in ellipses. Having absorbed William Gilbert’s recently published work on magnetism, with its thesis that the Earth itself was a giant magnet, Kepler extended this principle to all celestial bodies and hypothesized that the Sun’s anima motrix combined with its own magnetism and that of the planets to create the elliptical orbits.

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