Kepler's laws of planetary motion explaining how the planets' speeds varied, and using elliptical orbits rather than circular orbits with epicycles. Isaac Newton showed in 1687 that relationships like Kepler's would apply in the Solar System to a good approximation, as a consequence of his own laws of motion and law of universal gravitation. Kepler's laws improved the model of Copernicus. If the eccentricities of the planetary orbits are taken as zero, then Kepler basically agreed with Copernicus: The eccentricities of the orbits of those planets known to Copernicus and Kepler are small, so the foregoing rules give fair approximations of planetary motion, but Kepler's
Three Laws of Robotics inevitable result of the "Three Laws of Humanics". This story does not fit within the overall sweep of the "Robot" and "Foundation" series; if the George robots "did" take over Earth some time after the story closes, the later stories would be either redundant or impossible. Contradictions of this sort among Asimov's fiction works have led scholars to regard the "Robot" stories as more like "the Scandinavian sagas or the Greek legends" than a unified whole. Indeed, Asimov describes "—That Thou Art Mindful of Him" and "Bicentennial Man" as two opposite, parallel futures for robots that obviate the Three Laws