The Law Inside the Mysticism

Kepler's Third Law is now taught as a purely empirical relationship, one of three laws of planetary motion presented in physics and astronomy courses with the religious framework that originally produced it left aside entirely. That separation would have puzzled Kepler, who wrote Harmonices Mundi explicitly as an act of natural theology, an attempt to show that God had designed the cosmos according to the same harmonic proportions Pythagoras and Plato had identified in music and geometry centuries earlier, and who described his own astronomical calculations as a form of thinking God's thoughts after Him. The Third Law was, in his own presentation, evidence for that design, arrived at because he was looking for harmonic proportion in planetary motion and found one, not a result he stumbled on while pursuing a religiously neutral empirical program.

Isaac Newton later used Kepler's three laws of planetary motion, including the Third Law from this book, as essential empirical foundations for his own theory of universal gravitation, a use entirely disconnected from Kepler's Pythagorean motivations. That afterlife, a devout piece of natural theology becoming load-bearing infrastructure for a mechanistic physics its author would not have recognized as sharing his own purpose, is one of the more striking examples historians of science point to when arguing that religious and mystical motivation can produce genuinely durable scientific results, whatever became of the framework that generated them.