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When Kepler Destroyed the Universe
Ideas change everything
Science advances in fits and starts, at key moments moving from equilibrium to revolution. One of those significant moments was in 1609.
It is impossible for us today to appreciate the profound effect of Johannes Kepler’s theory of planetary motion. Before Kepler’s 1609 book Astronomia Nova, the unquestioned assumption was that everything in the heavens was perfect. This was not a strictly religious idea, though religion certainly accepted it. Most Ancient Greek philosophers readily agreed that the starry heavens above was a perfect realm of celestial spheres.
Central to the notion of cosmic perfection was the assumption that the motion of heavenly bodies must be circular. Since ancient times, the circle had been revered as geometric perfection. Scientists and sages assumed that the heavens were a realm of perfection and all motions of bodies reflected that perfection. Planets, assumed to revolve around the Earth of course, must revolve in circles.
The paradigm of circular motion was so strong that to explain retrograde planetary motion, astronomers developed the complicated theory of multiple epicycles. Planets revolved around a circle that revolved around the Earth, It was better to have dozens more circles in heaven than no circles at all. Even the heliocentric…
