It is almost impossible for us today to imagine the profound effect of Kepler’s theory of planetary motion (published in 1609). It was always an unquestioned assumption that everything in the heavens was pristine and perfect and that meant that the motion of heavenly bodies was circular. The paradigm of circular motion was so strong that it even tolerated the complicated theory of multiple epicycles – better to have dozens of more circles in heaven than no circles at all.
Ironically, it was Kepler who made the heavens more elegant and simpler by making the profound paradigm shift of imagining the planetary orbits as elliptical rather than circular. His system was so much more elegant than Copernicus’s. Suddenly no epicycles were needed and each planet moved in a single motion. However, it meant that God did not use perfect geometry in the Creation.
That shift in thinking, coupled with scientific work from many others, effected how intellectuals viewed their universe. If perfection was not the model for creation then the universe is a very different place. If we can’t argue from rational first principles to reality, but instead reality tells us something that violated our assumptions, then we have to change how we approach the universe. Knowledge had to be won by searching, not by reasoning to it.
Not that this changed everyone’s views. Spinoza, Leibniz, and others still believed that truth was known through analytical logic and Hobbes still demanded that science proceed from first principles rather than observations. Even Kepler later tried to save a pristine geometrical model of the heavens by attempting to craft a solar system where the planetary orbits expressed perfect geometrical shapes, despite their imperfect ellipses.
Regardless, after Kepler, the perfect Ptolemaic universe was destroyed forever.
