Johannes Kepler lived in a time of great upheaval- politically, religiously, and scientifically. As such, he engaged with issues that encompassed the sign of the changing times in the early modern world. The most notable of these, made famous by his contemporary Galileo Galilei, was the debate of heliocentrism within and among members of the church. Kepler was an ardent defender of Copernicus, who had first proposed the idea of a heliocentric model, and his most notable works The Mysterium Cosmographicum, Astronomia Nova, Harmonies, and the Epitome of Copernican Astronomy all utilize and defend heliocentrism as the central argument for duration of the work. While it certainly was a revolutionary idea for the time, Kepler was not solely interested in the heliocentric model as an end in itself. As a self-proclaimed astronomer-priest, Kepler sought to understand the grand design of the cosmos through a combination of mathematics, geometry, theology, astronomy, astrology, and even music. In investigating Copernicus’s claims he sought not only to construct an appropriate model for the movement of planets and other celestial bodies he observed, but construct a model of his own that explained their movement in relation to the architecture of the universe itself. Being one of the few remaining “Renaissance Men” of the era, Kepler sought to combine many different areas of knowledge into a unifying theory that would provide a satisfying explanation for certain aspects of the world as laid out by God.
In his investigation of the cosmos and more prominently the defense of Copernicus, Kepler developed a model to understand the motion of the planets that would become known as the three planetary laws, the most substantial contribution of Kepler’s to astronomical science. These laws were built on Copernican theory, and even advanced some facets of his arguments. Ultimately they were elaborated on by Kepler in the Astronomia Nova and the Harmonice Mundi in order for Kepler to reach a harmonious view of the planets and evaluate them not as individual entities but a larger system that followed the same set of rules. The first of these laws described planetary motion in an elliptical orbit. Prior to this postulation, the widely accepted theory was that the planets moved in circular orbits; Copernicus himself proposed his model with planetary orbits depicted as circles. The Ptolemaic model also proposed that the planets moved with varying velocities and altered accelerations, which explained why some planets when observed appeared to move away from the Earth through their orbit paths. Kepler’s second law modified this however, hypothesizing that varying motion in relation to the orbit of the sun was characteristic of the movement of the planets. This was justified in tandem with his third law of planetary motion which described the period of revolution of a planetary body being proportional between the perihelion (closest to the sun) and the aphelion (farthest from the sun) – in other words – the speed of the planet was directly related to distance from the sun. This would lay the groundwork for more developed theories of acceleration and gravity through further study of the planets’ movements (Newton’s laws of motion and gravity did not arrive until nearly seven decades after this theory, so Kepler’s contribution to physics cannot be understated). Implicated in these discoveries was the fact that Earth similarly obeyed these laws of planetary motion, and indeed was not exceptional by any means as previously outlined by the geocentric perspective. If cosmic insignificance was a sign of the turn from geocentrism to heliocentrism, Kepler still sought to affirm humanity’s place in the cosmos. He observed that the revolutionary periods of the planets were not only proportional to themselves, but to surrounding planets as well. In Harmonice Mundi, Kepler develops this idea to describe the apparent harmonic motion between the planets, in order to propose a unifying theory of harmony among all bodies. His pursuit for a model of cosmic harmony was the sole ambition of his life and work.
From the outset, Kepler’s theories seemed to be at odds with his desire for a harmonious universe. Rather than being the centerpiece of a cosmic symphony, the earth was now just a small player in a much larger universe, diminishing our own significance while simultaneously ascribing more importance to surrounding planets. In his Mysterium Cosmographicum, Kepler tackles this very issue, and uses heliocentrism itself as a justification for his theory of God’s design for the solar system and the universe at large. He used Platonic solids inscribed within the orbits of the planets to describe their motions, advancing Copernicus’ theories and providing a framework for further development, both by him and astronomers who came later who would classify Kepler’s model as the most accurate of the time. While heliocentrism was meant to disrupt the harmony established by the Ptolemaic system, Kepler instead improved upon its shortcomings and went on to describe a much more accurate model of the solar system.
Other philosophers before and during Kepler’s time had argued for a notion of harmony in nature, and used analogies of musical theory in order to describe observations in both nature and society. Kepler however took the meaning of harmony very literally and sought to describe the movement of the heavenly bodies with music itself. Indeed Pythagoras and Plato argued for a model of the cosmos and society based upon harmonies of music, respectively, and similarly Kepler desired a theory to unify all beings. An adept musical theorist himself, he developed an alternative version of Pythagoras’ model of the cosmos based on the angular velocities of the planets in relation to the sun, rather than distance to the earth. The perihelion and aphelion of each planet described a different musical scale, each in their own key which when played together produced polyphony, a combination of different melodies and voices. Although this relation in itself seemed satisfying, the related musical scales themselves produced dissonant tones, and sounded far away from the harmony that Kepler so ardently desired. He justified it not by adjusting the scales, but by commenting on the discord that is present in life and nature every day. Much like the conflict-ridden society that Kepler had been born into, nature experienced points of dissonance that may be displeasing in the moment, but would eventually resolve harmoniously and in complete unity. He postulated that the planets laid in harmony at the moment of Creation, and would again be harmonious at the Apocalypse. The harmony of society would similarly be present when many elements of discord are brought together – the collapse of the Holy Roman Empire, the emergence of schisms in Christianity amid the reformation, and the ever-widening rift between the papacy and the philosophers of the modern period all were but facets of the dissonance between people and systems that Kepler observed. At an appropriate time, he believed, these would come together and produce a harmonious solution that unified people regardless of their differences.
Bibliography
Kepler, Johannes. Harmonices Mundi (Harmony of the Worlds). 1619
Rothman, Aviva. “Johannes Kepler’s pursuit of harmony.” Physics Today. Jan 2020, 73;1, pp. 36. Web.
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