Beliefs of Johannes Kepler - Essay Example

JOHANNES KEPLER Being one of the most influencial theorists in astronomy and mathematics of the sixteenth and seventeenth centuries, Johannes Kepler (1571-1630) established and developed unique scientific method to astronomy, which later led Mittelstrass to explain that Copernican Revolution would be better named the Keplerian Revolution (Mittelstrass, 205). From the critical perspective, the Keplerian theory of knowledge constitutes historically unprecedented challenge to the scepticism that was prevalent in astronomy when it was proposed. Practically, Kepler was able to refute the challenge of the sceptic on many argumentative fronts, a fact that is itself a consequence of the tenets that are found in his position. Kepler's epistemology was profoundly concerned with astronomical practice, with methodological issues, and with the results of their application to the serious problems of late-renaissance astronomy. Kepler not only was able to ask questions in a way that no one had before asked, but he was able to provide answers to those questions that even now are worthy of continued study. From this perspective, Kepler was less the last great cosmologist of the classical tradition that includes Ptolemy and Copernicus; more was he the first cosmologist of the modern tradition. In the middle of the sixteenth century, fourteen centuries after the death of Ptolemy (c. A.D. 100-170), his Almagest still dominated all of astronomy. With the renaissance of interest in the works of the ancients, the relevance of the Ptolemy's great work had not only not diminished, but was on the increase (van Helden, 42). But by the end of the sixteenth century and the beginning of the seventeenth the Ptolemaic system was facing serious challenges. The subsequent revolutionary transformation from the geocentric to the heliocentric worldview has been almost universally attributed to the works of Nicholas Copernicus (1473-1543). Copernican astronomy is best known for the radical proposition that the Earth is in motion about the Sun rather than vice versa. Copernican heliocentrism emerged from a profound dissatisfaction with the fundamental principles upon which Ptolemy had based his system of the heavens. In particular, the Ptolemaic assumption of the punctum equans Copernicus viewed as contrary to the admissible explanations for the true motions of the planets. The punctum equans, or equant point, is an eccentric point about which the planet is supposed to subtend a uniform angular speed. Historically, published in 1956, Johannes Kepler's first and evidently most influencial astronomical work Mysterium Cosmographicum was the first major treatise after Copernicus' De revolutionibus to argue for heliocentrism (Gingerich, 347). Although Kepler has been defending the theory of Copernicus from the very beginning, with Mysterium Cosmographicum scientist provided a new kind of theory of the planets. His theory of the planets has been classified as new because it was the product of the first explicit and thorough attempt to consistently unify the epistemological structures of the hitherto divergent sciences of astronomy and physics (Koyre, 119). Kepler's objective in Mysterium Cosmographicum was nothing less than the development of a theory of the absolute structure of the world system. Kepler was certainly not the first to attempt to provide a general cosmographic account of the planets, that is, an account that seeks to explain the proportions of the universe as a whole. Both Ptolemy's and Copernicus' respective theories each maintain not only an ordering of the planetary orbs, but contain estimates of the ratios of their dimensions. But in the theory of Ptolemy these estimates are empirically underdetermined because of the independence of each planetary hypothesis, and in the theory of Copernicus, the estimates are strictly a posteriori consequences of the heliocentric hypothesis and, because of their reliance on Ptolemaic observations and mathematical constructions, no better corroborated empirically (Stephenson, 66). In Kepler's Mysterium Cosmographicum, however, his unification of the geometrical hypotheses of astronomy with the dynamical hypotheses of physics produces a theory that is not only predicated on the truth of physical heliocentrism, but attempts to generate the entire structure of the cosmos from this new principle. As Kepler was well aware, any salient argument to the true nature of the world system must exceed the limits of both astronomy and physics as prescribed by the contemporary interpretations of these disciplines. Such argument must address directly the related problems of evidential underdetermination and empirical equivalence that had led to the prevailing demarcation of astronomy as a purely mathematical discipline, and to the complex and varied interpretations of Copernicus' theory (Gingerich, 519). It was not the empirical success of Copernicus' theory that convinced Kepler of heliocentrism; the tables developed in accordance with the Copernican hypotheses were not much more precise than those based on the Ptolemaic hypotheses, and in some cases they were worse (Kozhamthadam, 132). Though the empirical adequacy of astronomical hypotheses was a necessary condition for Kepler, it was not sufficient. It was the cosmological component of Copernicus' writings that interested Kepler (Gingerich, 521). Indeed, one of the most consistent and outstanding features of Kepler's astronomical works is his enthusiastic support of the cosmological aspects of Copernicus' heliocentric hypothesis. While Kepler would challenge many of the fundamental assumptions of Copemicanism, even in the Mysterium, he was from a very early stage in his astronomical researches, and in a manner unlike any of his contemporaries, convinced that the centrality of the Sun is a physical truth. Indeed, his unprecedented synthesis of physics and heliocentric astronomy attests to the fact that he believed Copernicus' theory was not only the most mathematically elegant description of the motions of the planets but that it corresponds to the true nature of the world system. In the first chapter of the Mysterium, Kepler presents a cogent defense of heliocentrism. It is evident that Kepler considered that Copernicus, while inspired in his transformation of the center of the world-system from the Earth to the Sun, had failed to realize the full explanatory benefits that a heliocentric theory might provide. The physical Sun has far less causal relevance in Copernicus' theory than in Kepler's. To argue that the Sun is the center of the firmament and of the planets' motions, and, moreover, to argue that the Sun is the cause of the motions, are the paramount tasks of the Mysterium (Koyr, 128). Kepler called himself a follower of Copernicus, and this is accurate insofar as he adopted the Copernican tenets of the immobility of the Sun and the multiple motions of the Earth. However, the central epistemological claims of the Mysterium Cosmographicum are far more historically divergent than the term "Copernican" would indicate (Koyr, 134). Kepler vastly expanded the scope of the arguments in support of heliocentrism. For he realized that a consistent unification of the principles of physics and astronomy, and the subsequent constraining of hypotheses to these combined principles, were the means of distinguishing the true form of the world from those that are true in respect to appearances only. The epistemological criteria involved in the "linking of syllogisms" and the demand for "physical correlates to geometrical hypotheses" ensure that this unification is manifest in the heliocentric theory that Kepler proposes (Jardin, 141). These criteria of linked syllogistic logic and of physically determinate hypotheses not only allowed Kepler to demonstrate the logical advantages of heliocentrism over geocentrism in comparative geometric simplicity, but also allowed him to show that the assumption of physical heliocentrism could support a causal theory of the world system in a manner unlike any alternative theory. Furthermore, these epistemological criteria underwrote the remarkable methodological achievement of the Astronomia Nova, where the criteria were applied to the determination of the true motion of the planet Mars. Johannes Kepler's Astronomia Nova may justifiably be considered one of the most important works in the history of science. Its seventy brief chapters contain a truly new kind of natural philosophy. Four centuries after Kepler's speculations and investigations, contemporary scientists are fortunate to know which components of his philosophy were sound, both in terms of the conception he had of planetary motion and its causes, and in terms of the way he regarded the various sciences, their respective subjects, and their relations to one another. Kepler is often said to have shown that the planets orbit the way they do, and Newton why. The most common versions of this distinction maintain that Kepler was able to discover some of the regularities of planetary motion, and that these regularities would only later be explained in terms of Newtonian universal gravity. The soundness of this dichotomy, however, is premised upon our privileged position in history, as it might equally well be applied to Newtonian physics itself in comparison to Einsteinian physics. The theory of the Astronomia Nova did to the theories of Ptolemy, Copernicus and Brahe what Einstein's did to Newton's in a much later time: it invoked a new conceptualization of the regularities accounted for by the older theory and delivered an account, on the same conceptual basis, of regularities previously unperceived. From the critical perspective, contemporary assumption that the sciences of physics and astronomy are to be directly relevant to one another at all is itself an important and revolutionary claim defended within Kepler's philosophy. Kepler was arguably the first to recognize that the problem of the observational equivalence of astronomical hypotheses, if it were to be surmounted, would require the unification of astronomy with physics. In the Astronomia Nova Kepler placed both of the ancient scientific traditions of astronomy and physics together to found a new kind of theory of the motions of the planets - a theory that provided causal reasons for the facts of positional astronomy. In doing this he was attempting to provide sound causal explanations for astronomical regularities that, previous to the Astronomia Nova, were not even recognized as explicable in causal terms. BIBLIOGRAPHY Jardin, N. The birth of history and philosophy of science: Kepler's A Defence of Tycho against Ursus. Cambridge: Cambridge University Press, 1984. Gingerich, O., "Kepler and the New Astronomy", in Quarterly Journal of the Royal Astronomical Society 13, 1972, pp. 346-373 Gingerich, O., "From Copernicus to Kepler: Heliocentrism as a Model and as Reality", in Proceedings of the American Philosophical Society 117, 1973, pp. 513-522. Koyr, A., The Astronomical Revolution trans. Dr. R. E. W. Maddison. New York: Cornell UP, 1973 Kozhamthadam, J., The Discovery of Kepler's Laws, Notre Dame, University of Notre Dame Press, 1994. Mittelstrass, J., "Methodological Elements of Keplerian Astronomy", Studies in History and Philosophy of Science, Nov. 1972, 3(3), pp. 203-232 Stephenson, B., Kepler's Physical Astronomy, New York: Spinger-Verlag, 1987 van Helden, A., Measuring the Universe, Chicago: Chicago University Press, 1985 Read More