Pierre-Simon Laplace

Pierre-Simon Laplace was born in 1749 in Beaumont-en-Auge in Normandy, the son of a cider merchant who expected him to enter the Church. He went instead to the University of Caen to study mathematics, dropped out at nineteen with a letter of introduction to d'Alembert in Paris, and by twenty-four was professor of mathematics at the École Militaire — where he examined, with indifferent marks, a young Corsican named Napoleon Bonaparte. The political neutrality he maintained through the Revolution, Napoleon's empire, and the Bourbon restoration was so pronounced that his contemporaries coined a word for it: he was called serviceable.

His scientific project was the completion of Newton's Principia. Newton had shown that gravity governed the planets but had left open the question of whether the solar system was stable. Laplace proved, in a sequence of papers between 1773 and 1787, that the major perturbations are periodic rather than secular: the solar system is self-correcting. He collected this work into the five-volume Traité de mécanique céleste (1799–1825). When Napoleon asked him why the book never mentioned God, Laplace replied — or is said to have replied — "Sire, I had no need of that hypothesis."

For rotational dynamics, his contribution is the precession calculation. In the 1780s Laplace computed, from Newtonian gravity acting on the equatorial bulge, the 26,000-year precession of the equinoxes that Hipparchus had observed in 127 BCE, and the 18.6-year nutation caused by the tilted orbit of the Moon. It was the first planetary-scale gyroscopic calculation ever carried out, and it remains essentially correct. He also gave probability its modern analytical foundations in Théorie analytique des probabilités (1812), proving the central limit theorem and formalising Bayes' rule.