Sir Isaac Newton (25 December 1642 – 20 March 1727) was the greatest scientist of his time and, according to many, of all time: he perfected the theory of mechanics, created the first dynamical theory of gravity, and made fundamental experimental discoveries in optics. He also discovered the calculus and made a host of contributions to other branches of mathematics. His principal work was the Mathematical Principles of Natural Philosophy (1687), in which he set out the laws of motion that since bear his name, and deduced from astronomical observations (and particularly Kepler’s laws) both the universality of gravity as a force function and its form: the inverse square law.
Of Newton’s three laws of motion, only the third was original to Newton: the first was due to Descartes and the second to Huygens, who had also arrived at the law for centripetal acceleration. Throughout his life Newton distinguished himself by antagonism with his rivals, notably Descartes, Hooke, and Leibniz. His most extended published philosophical commentary on motion, the Scholium to the Definitions of Book 1 of the Principles, was in large part directed to refuting Descartes’ relationalist theory of motion. Newton held not only that ‘true’ or ‘absolute’ motion must be presupposed, in order that dynamical laws may defined, but that they were motions with respect to space itself, viewed as an immaterial, immovable substance, pervading the entire universe.
Whilst Newton showed, in the Principles, how his theory of motion and gravity could actually be applied, he claimed in addition to be able to determine absolute motion, contrary to the relativity principle (itself deduced from the Laws). The question of the nature or need of ‘absolute’ motions continued to preoccupy philosophers and physicists throughout the eighteenth and nineteenth centuries, and provided a significant impetus for Einstein’s discoveries.
Newton articulated a broadly empiricist philosophy of science, explicitly in his Rules of Reasoning in Philosophy at the beginning of Book 3 of the third edition of the Principles, and implicitly in his derivation of the inverse square law from astronomical data (but using the Laws). The action-at-a-distance implicit in the idea of a force function (that is a function of the positions of bodies alone) encountered considerable resistance, as contrary to the rationalistic principles of the corpuscularian philosophy: his Rules of Reasoning, in particular the 4th, were directed to such criticisms. Whilst Newton believed an underlying mechanism for the transmission of gravitational forces might be found, he considered speculation on the topic unproductive unless informed by experiment, and a fortiori that theories that had been confirmed by induction (such as his own theory) were not susceptible to criticism on this score. In the Opticks (1704), in contrast, Newton engaged in several speculations as to the nature of light and magnetism. In correspondence (particularly with Bishop Bentley) he also speculated on the question of the stability of the universe.
Newton was born in Woolshorpe Manor in Woolsthorpe-by-Colsterworth in Lincolnshire, and was educated at the King’s School, Grantham, and Trinity College, Cambridge. He was elected to the chair of Lucasian Professor of Mathematics in 1669. In his later years he lived in London, where he served as President of the Royal Society and Master of the Mint.