Passion of the Western Mind

by Tarnas, Richard

  If the Moon’s surface was uneven, like the Earth’s, and if the Sun had spots that came and went, then these bodies were not the perfect, incorruptible, and immutable celestial objects of Aristotelian-Ptolemaic cosmology. Similarly, if Jupiter was a moving body and yet could also have four moons revolving around it while its entire system revolved in a greater orbit, then the Earth could also do the same with its own moon—thus refuting the traditional argument that the Earth could not move around the Sun, or else the Moon would have long ago spun off its orbit. And again, if phases of Venus were visible, then Venus must be revolving around the Sun. And if the Milky Way, which to the naked eye was just a nebulous glow, now proved to be composed of a multitude of new stars, then the Copernican suggestion of a much larger universe (to explain the lack of visible annual stellar parallax despite the Earth’s movement around the Sun) seemed considerably more plausible. And if the planets now appeared through the telescope to have substantial bodies with extended surfaces and were not just points of light, and yet many more stars were visible without any apparent extension, then this also argued in favor of an incomparably larger universe than that assumed by the traditional cosmology. After several months of such discoveries and conclusions, Galileo quickly wrote his Sidereus Nuncius (The Messenger of the Stars), making public his first observations. The book created a sensation in European intellectual circles.

  With Galileo’s telescope, the heliocentric theory could no longer be considered merely a computational convenience. It now had visible physical substantiation. Moreover, the telescope revealed the heavens in their gross materiality—not transcendent points of celestial light, but concrete substances appropriate for empirical investigation, just like natural phenomena on the Earth. The time-honored academic practice of arguing and observing exclusively from within the boundaries of Aristotelian thought began giving way to a fresh examination of empirical phenomena with a critical eye. Many individuals not previously involved in scientific studies now took up the telescope and saw for themselves the nature of the new Copernican universe. Astronomy, by virtue of the telescope and Galileo’s compelling writings, became of vital interest to more than specialists. Successive generations of late Renaissance and post-Renaissance Europeans, increasingly willing to doubt the absolute authority of traditional doctrines both ancient and ecclesiastical, were finding the Copernican theory not only plausible but liberating. A new celestial world was opening up to the Western mind, just as a new terrestrial world was being opened by the global explorers. Although the cultural consequences of Kepler’s and Galileo’s discoveries were gradual and cumulative, the medieval universe had effectively been dealt its death blow. The Copernican revolution’s epochal triumph in Western thought had begun.

  It is possible the Church could have reacted to this triumph otherwise than it did. Seldom in its history had the Christian religion attempted to suppress so rigidly a scientific theory strictly on the basis of apparent scriptural contradictions. As Galileo himself pointed out, the Church had long been accustomed to sanctioning allegorical interpretations of the Bible whenever the latter appeared to conflict with scientific evidence. He quoted the early Church fathers to that effect, and added that it would be “a terrible detriment for the souls if people found themselves convinced by proof of something that it was made then a sin to believe.” Moreover, many ecclesiastical authorities recognized Galileo’s genius, including several Jesuit astronomers in the Vatican. Indeed, the pope himself was a friend of Galileo and accepted with enthusiasm the dedication of his book, Assayer, which had outlined the new scientific method. Even Cardinal Bellarmine, the Church’s chief theologian, who finally made the decision to declare Copernicanism “false and erroneous,” had earlier written:

  If there were a real proof that the Sun is in the center of the universe, that the Earth is in the third heaven, and that the Sun does not go round the Earth but the Earth round the Sun, then we should have to proceed with great circumspection in explaining passages of Scripture which appear to teach the contrary, and rather admit that we did not understand them than declare an opinion to be false which is proved to be true.2

  But a unique and potent combination of circumstances conspired otherwise. The Church’s pervasive awareness of the Protestant threat compounded the challenge of any novel and potentially heretical position. With the memory of the Bruno heresy still fresh, Catholic authorities earnestly desired to avoid a new scandal that might further disrupt Reformation-torn Christianity. Making the issue all the more threatening were the new power of the printing press and the lucid persuasiveness of Galileo’s vernacular Italian, undermining the Church’s attempts to control the beliefs of the faithful. Also complicating the Church’s reaction were the intricate political conflicts in Italy involving the pope. A pivotal role was played by the Aristotelian professors in the universities, whose intense opposition to the vociferously anti-Aristotelian and all-too-popular Galileo served to arouse fundamentalist preachers, who in turn aroused the Inquisition. Galileo’s own polemical and even vitriolic personality, which alienated his opponents to the point of vengeance, was a contributing factor, as was his insufficient sensitivity to the profound significance of the greater cosmological revolution taking place. Bellarmine’s conviction that mathematical hypotheses were only intellectual constructs with no ultimate relation to physical reality; Galileo’s espousal of atomism, when the Catholic doctrine of the eucharistic transubstantiation seemed to require an Aristotelian physics; the pope’s sense of personal betrayal, exacerbated by his political insecurity; the power struggles between different religious orders within the Church; the Inquisition’s voracious appetite for punitive repression—all these factors coalesced with fateful accord to motivate the Church’s official decision to prohibit Copernicanism.

  That decision caused irreparable harm to the Church’s intellectual and spiritual integrity. Catholicism’s formal commitment to a stationary Earth drastically undercut its status and influence among the European intelligentsia. The Church would retain much power and loyalty in the succeeding centuries, but it could no longer justifiably claim to represent the human aspiration toward full knowledge of the universe. After the Inquisition’s ban, Galileo’s writings were smuggled to the north, where the vanguard of the Western intellectual quest would thereafter reside.3 Whatever the relative importance of individual factors such as the entrenched Aristotelian academic opposition or the pope’s personal motives, the ultimate cultural meaning of the Galilean conflict was that of Church versus science, and, by implication, religion versus science. And in Galileo’s forced recantation lay the Church’s own defeat and science’s victory.

  Institutional Christianity as a whole suffered from the Copernican victory, which contravened both religious foundations—Protestantism’s literal Bible and Catholicism’s sacramental authority. For the present, most European intellectuals, including the scientific revolutionaries, would remain devoutly Christian. But the schism between science and religion—maintained even within the individual mind—had fully announced itself. With Luther, the West’s intellectual independence had asserted itself within the realm of religion. With Galileo, it took a step outside of religion altogether, established new principles, and opened new territory.

  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 w
as 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. Kepler thereby made the first proposal that the planets in their orbits were moved by mechanical forces, rather than by the automatic geometrical motion of the Aristotelian-Ptolemaic spheres. Despite its relatively primitive form, Kepler’s concept of the solar system as a self-governing machine based on notions of terrestrial dynamics correctly anticipated the emerging cosmology.

  In the meantime, Galileo had pursued this mechanical-mathematical mode of analysis on the terrestrial plane with systematic rigor and extraordinary success. Like his fellow Renaissance scientists Kepler and Copernicus, Galileo had imbibed from the Neoplatonic Humanists the belief that the physical world could be understood in geometrical and arithmetic terms. With Pythagorean conviction he declared that “the Book of Nature is written in mathematical characters.” But with his more down-to-earth sensibility, Galileo developed mathematics less as a mystical key to the heavens than as a straightforward tool for the understanding of matter in motion and for the defeat of his Aristotelian academic opponents. Although Kepler’s understanding of celestial motion was more advanced than that of Galileo (who, like Copernicus, still believed in self-sustaining circular motion), it was Galileo’s insights into terrestrial dynamics that, when applied by his successors to the heavens, would begin to solve the physical problems created by Copernicus’s innovation.

  Aristotle’s physics, based on perceptible qualities and verbal logic, still ruled most contemporary scientific thinking and dominated the universities. But Galileo’s revered model was Archimedes the mathematical physicist (whose writings had been recently rediscovered by the Humanists), rather than Aristotle the descriptive biologist. To combat the Aristotelians, Galileo developed both a new procedure for analyzing phenomena and a new basis for testing theories. He argued that to make accurate judgments concerning nature, scientists should consider only precisely measurable “objective” qualities (size, shape, number, weight, motion), while merely perceptible qualities (color, sound, taste, touch, smell) should be ignored as subjective and ephemeral. Only by means of an exclusively quantitative analysis could science attain certain knowledge of the world. In addition, while Aristotle’s empiricism had been predominantly a descriptive and, especially as exaggerated by later Aristotelians, logico-verbal approach, Galileo now established the quantitative experiment as the final test of hypotheses. Finally, to further penetrate nature’s mathematical regularities and true character, Galileo employed, developed, or invented a host of technical instruments—lens, telescope, microscope, geometric compass, magnet, air thermometer, hydrostatic balance. The use of such instruments gave a new dimension to empiricism unknown to the Greeks, a dimension that undercut both the theories and the practice of the Aristotelian professors. In Galileo’s vision, free exploration of an impersonal mathematical universe was to replace the hidebound academic tradition’s interminable deductive justification of Aristotle’s organismic universe.

  Employing the new categories and new methodology, Galileo set out to demolish the spurious dogma of academic physics. Aristotle had believed that a heavier body would fall at a faster rate than a lighter one, because of its elemental propensity to seek the center of the Earth as its natural position—the heavier the body, the greater the propensity. Through his repeated application of mathematical analysis to physical experiments, Galileo first refuted this tenet and later formulated the law of uniform accelerated motion in falling bodies—a motion that was independent of the weight or composition of the bodies. Building on the impetus theory of Aristotle’s Scholastic critics Buridan and Oresme, Galileo analyzed projectile motion and developed the crucial idea of inertia. Contrary to Aristotle, who held that all bodies sought their natural place and that nothing continued to move otherwise without a constantly applied external push, Galileo stated that just as a body at rest would tend to remain so unless otherwise pushed, so too would a moving body tend to remain in constant motion unless otherwise stopped or deflected. Force was required to explain only change in motion, not constant motion. In this way, he met one of the Aristotelians’ chief physical arguments against a planetary Earth—that objects on a moving Earth would be forcibly knocked about, and that a projectile thrown directly upward from a moving Earth would necessarily land at some distance away from its point of departure. Since neither of these phenomena was observed, they concluded that the Earth must be stationary. Through his concept of inertia, however, Galileo demonstrated that a moving Earth would automatically endow all its objects and projectiles with the Earth’s own motion, and therefore the collective inertial motion would be imperceptible to anyone on the Earth.

  In the course of his life’s work, Galileo had effectively supported the Copernican theory, initiated the full mathematization of nature, grasped the idea of force as a mechanical agent, laid the foundations of modern mechanics and experimental physics, and developed the working principles of modern scientific method. But the question of how to explain physically the celestial movements, including the motion of the Earth itself, still remained unresolved. Because Galileo had missed the significance of the planetary laws discovered by his contemporary Kepler, he had continued to maintain the traditional understanding of celestial motion as circular orbits, only now centered around the Sun. His concept of inertia—which he understood as applicable on the Earth only to motion on horizontal surfaces (where gravity was not a factor) and which was thus circular motion around the Earths’s surface—was applied to the heavens accordingly: The planets continued to move in their orbits about the Sun because their natural inertial tendency was circular. Galileo’s circular inertia, however, could not explain Kepler’s ellipses. And it was all the more implausible if the Earth, which as the unique center of the universe in Aristotelian cosmology had defined the surroun
ding space and given an absolute motive and reference point for circling spheres, was now understood to be a planet. The Copernican universe had created and was still plagued by a fundamental enigma.

  But now occurred another influx of ancient Greek philosophy: the atomism of Leucippus and Democritus, which would both point toward a solution to the problem of celestial motion and help shape the future course of Western scientific development. The philosophy of atomism, as passed on by Democritus’s successors Epicurus and Lucretius, had resurfaced during the Renaissance as part of the Humanists’ recovery of ancient literature, particularly through the manuscript of Lucretius’s poem De Rerum Natura (On the Nature of Things), outlining the Epicurean system. Originally developed as an attempt to meet the logical objections against change and motion put forward by Parmenides, Greek atomism had posited a universe made up of invisibly small, indivisible particles moving freely in an infinite neutral void, and creating by their collisions and combinations all phenomena. In this void there was no absolute up or down or universal center, every position in space being neutral and equal to every other. Since the entire universe was composed of the same material particles on the same principles, the Earth itself was merely another chance aggregation of particles and was neither at rest nor at the universe’s center. There was therefore no fundamental celestial-terrestrial division. And since both the size of the void and the number of particles were infinite, the universe was potentially populated by many moving earths and suns, each created by the atoms’ random movements.

  The evolving Copernican universe bore a number of striking resemblances to this conception. Making the Earth a planet had removed the foundation from the Aristotelian idea of an absolute (nonneutral) space centered on the stationary Earth. A planetary Earth also required a much larger universe to satisfy the absence of observable stellar parallax. With the Earth no longer the universal center, the universe did not have to be finite (a universal center requires a finite universe, since an infinite space can have no center). The outermost sphere of stars was now unnecessary as an explanation for the movement of the heavens, and so the stars could be dispersed infinitely, as the Neoplatonists had also suggested. And Galileo’s telescopic discoveries had both revealed a multitude of new stars at apparently great distances, and further undermined the celestial-terrestrial dichotomy. The implications of a Copernican universe—a nonunique moving Earth; a neutral, centerless, multipopulated, and perhaps infinite space; and the elimination of the celestial-terrestrial distinction—all coincided with those of the atomistic cosmos. With the comprehensive structure of Aristotelian cosmology collapsing, and with no other viable alternative to replace it, the atomists’ universe represented an already well-developed and uniquely appropriate framework into which the new Copernican system could be placed. The esoteric philosopher-scientist Bruno was the first to perceive the congruence between the two systems. Through his work, the Neoplatonic image of an infinite universe enunciated by Nicholas of Cusa was reinforced by the atomistic conception to create an immensely expanded Copernican cosmos.