In the early 1660s Newton left Cambridge during a plague closure and returned to his mother's farm in Lincolnshire. In those years — which he later called his anni mirabiles — he laid the foundations of the differential calculus, understood the decomposition of white light into colours, and devised a force law that could explain the motion of the planets: gravitation.

But he did not fully publish these results for twenty years. Eventually, urged on by the astronomer Edmond Halley (who largely paid for the printing himself), Philosophiae Naturalis Principia Mathematica appeared in 1687. The three-volume work formulates the three laws of motion, sets out the law of universal gravitation, and derives Kepler's planetary orbits from these laws mathematically.

The Principia's true revolution lies in the reach of its consequences: the same equations describe the Moon's orbit and the fall of an apple; sky and earth are no longer two separate realms governed by different laws, but parts of a single coherent system. The idea shaped the entire subsequent structure of science — 19th-century electrodynamics, 20th-century thermodynamics, even relativity began from the Newtonian frame and pressed it to its limits. Newtonian physics also became the engineering foundation of the Industrial Revolution: bridges, machines, ballistics, ship design.