But atomism was to provide other and no less consequential contributions to the developing cosmology. For not only was the structure of the atomistic cosmos congruent with the Copernican theory, but, in addition, the atomistic conception of matter itself was singularly appropriate to the working principles of the new natural scientists. Democritus’s atoms were characterized exclusively by quantitative factors—size, shape, motion, and number—and not by any perceptible qualities, such as taste, smell, touch, or sound. All apparent qualitative changes in phenomena were created by differing quantities of atoms combined in different arrangements, and therefore the atomistic universe was in principle open to mathematical analysis. The material particles possessed neither purpose nor intelligence, but moved solely according to mechanical principles. Thus the cosmological and physical structures of ancient atomism invited the very modes of analysis—mechanistic and mathematical—already being chosen and rapidly developed by seventeenth-century natural scientists. Atomism influenced Galileo in his approach to nature as matter in motion, was admired by Francis Bacon and employed by Thomas Hobbes in his philosophy of mechanistic materialism, and was popularized in European scientific circles by their younger contemporary Pierre Gassendi. But it was finally René Descartes who undertook the task of systematically adapting atomism to provide a physical explanation for the Copernican universe.
The basic principles of ancient atomism offered many parallels to Descartes’s image of nature as an intricate impersonal machine strictly ordered by mathematical law. Like Democritus, Descartes assumed that the physical world was composed of an infinite number of particles, or “corpuscles,” which mechanically collided and aggregated. As a Christian, however, he assumed that these corpuscles did not move in utterly random fashion, but obeyed certain laws imposed on them by a providential God at their creation. To discover those laws was Descartes’s challenge, and his first step was to ask how a single corpuscle would freely move in an infinite universe possessing neither absolute directions nor Aristotelian elemental tendencies to motion. By employing the Scholastics’ impetus theory in the new context of an atomistic space, he concluded that a corpuscle at rest would tend to remain at rest unless otherwise pushed, while a corpuscle in motion would tend to continue moving in a straight line at the same speed unless otherwise deflected. Thus Descartes enunciated the first unequivocal statement of the law of inertia—one that included the critical element of inertial linearity (compared with Galileo’s more rudimentary and empirically conceived Earth-oriented inertia with its implication of circularity). Descartes additionally reasoned that since all motion in a corpuscular universe must in principle be mechanistic, any deviations from these inertial tendencies must occur as a result of corpuscular collisions with other corpuscles. The basic principles governing these collisions he set out to establish by intuitive deduction.
With its freely moving particles in an infinite neutral space, atomism had suggested a new way of looking at motion. Descartes’s notion of corpuscular collision allowed his successors to develop further Galileo’s insights into the nature of force and momentum. But of immediate significance for the Copernican theory, Descartes applied his theories of linear inertia and corpuscular collision to the problem of planetary motion, and thereby began to clear away the last residue of Aristotelian physics from the heavens. For the automatic circular motions of the celestial bodies still espoused by Copernicus and Galileo were not possible in an atomistic world in which particles could only move in a straight line or remain at rest. By applying his inertial and corpuscular theories to the heavens, Descartes isolated the crucial missing factor in the explanation of planetary motion: Unless there was some other inhibiting force, the inertial motion of the planets, including that of the Earth, would necessarily tend to propel them in a tangential straight line away from the curving orbit around the Sun. Since, however, their orbits were maintained in continuous closed curves without such centrifugal breaks, it was evident that some factor was forcing the planets toward the Sun—or as Descartes and his successors more revealingly formulated it, something was continually forcing the planets to “fall” toward the Sun. To discover what force caused that fall was the fundamental celestial dilemma facing the new cosmology. The fact that the planets moved at all was now explicable by inertia. But the form that motion took—the planets’ constant maintenance of elliptical orbits about the Sun—still demanded explanation.
Many of Descartes’s intuitively deduced hypotheses concerning his corpuscular universe—including most of his laws of corpuscular collision and his filling the universe with vortices of moving corpuscles (by which he tried to explain the planets’ being pushed back into their orbits)—were not retained by his successors. But his basic conception of the physical universe as an atomistic system ruled by a few mechanistic laws became the guiding model for seventeenth-century scientists grappling with the Copernican innovation. And because the riddle of planetary motion still remained the outstanding problem for post-Copernican science in its efforts to establish a self-consistent cosmology, Descartes’s isolation of the “fall” factor was indispensable. With Descartes’s concept of inertia applied to Kepler’s ellipses, and with the general principle of mechanistic explanation implicit in both their rudimentary theories of planetary motion (Kepler’s anima motrix and magnetism, Descartes’s corpuscular vortices), the problem had gained a definition within which subsequent scientists—Borelli, Hooke, Huygens—could fruitfully work. Galileo’s terrestrial dynamics had further defined the problem by effectively contravening Aristotelian physics, and by giving precise mathematical measurements of heavy bodies falling to the Earth. Thus two fundamental questions remained, one celestial and one terrestrial: Given inertia, why did the Earth and other planets continually fall toward the Sun? And given a moving noncentral Earth, why did terrestrial objects fall to the Earth at all?
The possibility that both questions could have the same answer had been constantly growing with the work of Kepler, Galileo, and Descartes. The notion of an attractive force acting between all material bodies had also been developing. Among the Greeks, Empedocles had posited such a force. Among the Scholastics, Oresme had reasoned that if Aristotle were mistaken about the Earth’s unique central position, an alternative explanation for bodies’ falling to the Earth could be that matter naturally tended to attract other matter. Both Copernicus and Kepler had invoked such a possibility to defend their moving Earth. By the third quarter of the seventeenth century, Robert Hooke had clearly glimpsed the synthesis: that a single attractive force governed both planetary motions and falling bodies. Moreover, he mechanically demonstrated his idea with a pendulum swung in an elongated circular path, its linear motion being continuously deflected by a central attraction. Such a demonstration tellingly illustrated the relevance of terrestrial mechanics for the explanation of celestial phenomena. Hooke’s pendulum signaled the extent to which the scientific imagination had radically transformed the heavens from being a transcendent realm with its own special laws to being in principle no different from the mundane realm of the Earth.
It finally fell to Isaac Newton, born on Christmas Day the year of Galileo’s death, to complete the Copernican revolution by quantitatively establishing gravity as a universal force—a force that could simultaneously cause both the fall of stones to the Earth and the closed orbits of the planets around the Sun. Indeed, it was Newton’s astounding achievement to synthesize Descartes’s mechanistic philosophy, Kepler’s laws of planetary motion, and Galileo’s laws of terrestial motion in one comprehensive theory. In an unprecedented series of mathematical discoveries and intuitions, Newton established that to maintain their stable orbits at the relative speeds and distances specified by Kepler’s third law, the planets must be pulled toward the Sun with an attractive force that decreased inversely as the square of the distance from the Sun, and that bodies falling toward the Earth—not only a nearby stone but also the distant Moon—conformed to the same law. Moreover, he mathematically
derived from this inverse-square law both the elliptical shapes of the planetary orbits and their speed variation (equal areas in equal times) as defined by Kepler’s first and second laws. Thus all the major cosmological problems confronting the Copernicans were at last solved—what moved the planets, how they remained in their orbits, why heavy objects fall toward the Earth, the basic structure of the universe, the issue of the celestial-terrestrial dichotomy. The Copernican hypothesis had provoked the need for, and now found, a new, comprehensive, and self-consistent cosmology.
With an exemplary combination of empirical and deductive rigor, Newton had formulated a very few overarching laws that appeared to govern the entire cosmos. Through his three laws of motion (of inertia, force, and equal reaction) and the theory of universal gravitation, he not only established a physical basis for all of Kepler’s laws, but was also able to derive the movements of the tides, the precession of the equinoxes, the orbits of comets, the trajectory motion of cannonballs and other projectiles—indeed, all the known phenomena of celestial and terrestrial mechanics were now unified under one set of physical laws. Every particle of matter in the universe attracted every other particle with a force proportional to the product of their masses and inversely proportional to the square of the distance between them. Newton had struggled to discover the grand design of the universe, and had patently succeeded. Descartes’s vision of nature as a perfectly ordered machine governed by mathematical laws and comprehensible by human science was fulfilled.
Although Newton’s working concept of gravity as a force acting at a distance—a concept transposed from his studies of the sympathies and antipathies of Hermetic philosophy and alchemy—seemed esoteric and insufficiently mechanical to continental mechanistic philosophers, and puzzled even Newton, the mathematical derivations were too spectacularly comprehensive not to be compelling. Through the concept of a quantitatively defined attractive force, he had integrated the two major themes of seventeenth-century science—the mechanistic philosophy and the Pythagorean tradition. It was not long before both his method and his conclusions were recognized as the paradigm of scientific practice. In 1686–87, the Royal Society of London published Newton’s Principia Mathematica Philosophiae Naturalis. During the following decades, his achievement was celebrated as the triumph of the modern mind over ancient and medieval ignorance. Newton had revealed the true nature of reality: Voltaire called him the greatest man who ever lived.
The Newtonian-Cartesian cosmology was now established as the foundation for a new world view. By the beginning of the eighteenth century, the educated person in the West knew that God had created the universe as a complex mechanical system, composed of material particles moving in an infinite neutral space according to a few basic principles, such as inertia and gravity, that could be analyzed mathematically. In this universe, the Earth moved about the Sun, which was one star among a multitude, just as the Earth was one planet among many, and neither Sun nor Earth was at the center of the universe. A single set of physical laws governed both the celestial and the terrestrial realms, which were thus no longer fundamentally distinct. For just as the heavens were composed of material substances, so were their motions impelled by natural mechanical forces.
It also seemed reasonable to assume that after the creation of this intricate and orderly universe, God removed himself from further active involvement or intervention in nature, and allowed it to run on its own according to these perfect, immutable laws. The new image of the Creator was thus that of a divine architect, a master mathematician and clock maker, while the universe was viewed as a uniformly regulated and fundamentally impersonal phenomenon. Man’s role in that universe could best be judged on the evidence that, by virtue of his own intelligence, he had penetrated the universe’s essential order and could now use that knowledge for his own benefit and empowerment. One could scarcely doubt that man was the crown of creation. The Scientific Revolution—and the birth of the modern era—was now complete.
The Philosophical Revolution
The career of philosophy during these pivotal centuries was intimately tied to the Scientific Revolution, which it accompanied and stimulated, for which it provided a foundation, and by which it was critically molded. Indeed, philosophy now acquired an entirely new identity and structure as it entered into its third great epoch in the history of the Western mind. During much of the classical era, philosophy, though influenced by both religion and science, had held a largely autonomous position as definer and judge of the literate culture’s world view. With the advent of the medieval period, the Christian religion assumed that preeminent status, while philosophy took on a subordinate role in the joining of faith to reason. But with the coming of the modern era, philosophy began to establish itself as a more fully independent force in the intellectual life of the culture. More precisely, philosophy now commenced its momentous transfer of allegiance from religion to science.
Bacon
In the same decades of the early seventeenth century during which Galileo in Italy was forging the new scientific practice, Francis Bacon in England proclaimed the birth of a new era in which natural science would bring man a material redemption to accompany his spiritual progress toward the Christian millennium. For Bacon, the discovery of the New World by the global explorers demanded a corresponding discovery of a new mental world in which old patterns of thinking, traditional prejudices, subjective distortions, verbal confusions, and general intellectual blindness would be overcome by a new method of acquiring knowledge. This method was to be fundamentally empirical: through the careful observation of nature and the skillful devising of many and varied experiments, pursued in the context of organized cooperative research, the human mind could gradually elicit those laws and generalizations that would give man the understanding of nature necessary for its control. Such a science would bring man immeasurable benefits and reestablish that mastery over nature he had lost with the fall of Adam.
While Socrates had equated knowledge with virtue, Bacon equated knowledge with power. Its practical usefulness was the very measure of its validity. With Bacon, science took on a new role—utilitarian, Utopian, the material and human counterpart to God’s plan of spiritual salvation. Man was created by God to interpret and hold dominion over nature. The pursuit of natural science was therefore his religious obligation. Man’s primal fall required that such a pursuit be painstaking and fallible, but if he would discipline his mind and purify his vision of nature from age-old prejudices, man would achieve his divine right. Through science, the man of the modern era could assert his true superiority over the ancients. History was not cyclical, as was supposed by the ancients, but progressive, for man now stood at the dawn of a new, scientific civilization.
Skeptical of received doctrines and impatient with the syllogisms of the Aristotelian Scholastics, which he saw as nothing more than long-respected obstacles to useful knowledge, Bacon insisted that progress in science required a radical reformulation of its foundations. The true basis of knowledge was the natural world and the information it provided through the human senses. To fill the world with assumed final causes, as did Aristotle, or with intelligible divine essences, as did Plato, was to obscure from man a genuine understanding of nature on its own terms, solidly based on direct experimental contact and inductive reasoning from particulars. No longer should the pursuer of knowledge start from abstract definitions and verbal distinctions and then reason deductively, forcing the phenomena into prearranged order. Instead, he must begin with the unbiased analysis of concrete data and only then reason inductively, and cautiously, to reach general, empirically supported conclusions.
Bacon criticized Aristotle and the Scholastics for depending so heavily on deduction for their knowledge, since the premises from which deduction proceeded might simply be a spurious concoction of the philosopher’s mind with no foundation in nature. From Bacon’s point of view, all pure reason could accomplish in such circumstances would be to spin out of itself a web of abstractions
possessing no objective validity. By contrast, the true philosopher directly approached the real world and studied it, without falsely anticipating and prejudicing the outcome. He cleansed the mind of its subjective distortions. The Aristotelian search for formal and final causes, the a priori belief that nature possessed teleological purposes and archetypal essences, were just such distortions, deceptively attractive to the emotionally tainted intellect. They should be discarded as useless, barren of empirical fruit. The traditional philosophers’ Forms were merely fictions, and their words were prone to obscure rather than reveal. Preconceptions and verbiage must be renounced in favor of direct attention to things and their observed orderings. No “necessary” or “ultimate” truths should be so blithely assumed. To discover nature’s true order, the mind must be purified of all its internal obstacles, purged of its habitual tendencies to produce rational or imaginary wish fulfillments in advance of empirical investigation. The mind must humble itself, rein itself in. Otherwise science would be impossible.
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