Over two decades elapsed from Isaac Newton’s notable period of intellectual development in the mid-1660s to his eventual composition of the “Principia.” This phase of Newton’s life is frequently idealized with legends, particularly concerning his initial formulation of universal gravitation. A widespread tale is the apple anecdote and the “Annus Mirabilis,” suggesting that within a single year, Newton unveiled calculus, optics, and gravity. These legends endure partly due to Newton’s retrospective assertions.
In the 1660s, Newton investigated ideas of motion and gravity, influenced by Descartes, although his research was not yet fully realized. His “Waste Book” features notes contrasting lunar and terrestrial gravity without entirely embracing the law of inertia. Rather, he leaned on Kepler’s laws and the dynamics of circular motion, foreshadowing the inverse-square law essential to gravitational theory.
Newton’s later-life statements frequently sought to establish his precedence in scientific breakthroughs, particularly in conflicts such as the one with Leibniz regarding calculus and to refute claims by Robert Hooke, who implied that Newton’s concepts of gravity originated from him. Hooke corresponded with Newton about planetary motion, alluding to universal gravitation, yet failed to deliver a rigorous mathematical proof, in contrast to Newton’s subsequent work.
A pivotal moment transpired in 1684 during a discussion at a coffee house in London with Hooke, Christopher Wren, and Edmond Halley. The conversation focused on validating that an inverse-square law of gravity would result in Kepler’s elliptical orbits. Halley’s visit to Newton led to Newton demonstrating this connection, along with additional insights in his treatise “De Motu Corporum in Gyrum,” astonishing Halley with its potential to transform celestial mechanics.
Halley acknowledged the treatise’s significance and urged Newton to elaborate on it. Newton’s later revisions and publication endeavors culminated in the three-volume “Philosophiæ Naturalis Principia Mathematica” in 1687. This groundbreaking work established Newton’s laws of motion and universal gravitation as fundamental scientific tenets, profoundly shaping the scientific comprehension of the natural world.