2018-11-27

As far as kepler was concerned,elliptical orbits were merely an ad hoc hypothesis,and a rather repugnant one at that,because ellipses were clearly less perfect than circles. Having discovered almost by accident that elliptical orbits fit the observations well,he could not reconcile them with his idea that the planets were made to orbit the suum by magnetic forces. An explanation was provided only much later,in1687,when Sir Isaac Newton published his Philosophiae Naturalis Principia Mathematica,Probably the most important single work ever published in the physical sciences.In it Newton not only put forward a theory of how bodies move in space and time,but he also developed the complicated mathematics needed to analyze those motions.In addition,Newtion postulated a law of universal was attracted toward every other body by a force that was stronger the more massive the bodies and the closer they were to each other .It was this same force that caused objects to fallto the gground.(The story that Newton was inspired by an apple hitting his head is almost certainly apocryphal.All Newton himself ever said was that the idea of gravity came to him as he sat "in a contemplative mood" and "was occasioned by the fall of an apple.")Newton went on to show that,according to his law,gravity causes the moon to move in an elliptical orbit around the earth and causes the earth and the planets to follow elliptical paths around the sum.      OUR PICTURE OF THE UNIVERSE P4-5