Pierre-Simon Laplace was a French physicist and mathematician who remembered as one of the greatest scientists of all time, sometimes referred to as a French Newton or Newton of France, with a phenomenal natural mathematical faculty possessed by none of his contemporaries. He placed the capstone on mathematical astronomy by summarizing and extending the work of his predecessors in his five volume Mécanique Céleste (Celestial Mechanics) (1799-1825). This work was important because it translated the geometrical study of mechanics used by Newton to one based on calculus, known as physical mechanics. Laplace proved the dynamical stability of the solar system (with tidal friction ignored) on short time scales. On long time scales, however, this assertion was proven false in the early 1990s. He restated and developed the nebular hypothesis of the origin of the solar system and was one of the first scientists to postulate the existence of black holes and the notion of gravitational collapse.

In mathematics, Laplace contributed the Laplace transform and Laplace's equation. In 1812, Laplace issued his Théorie analytique des probabilités in which he laid down many fundamental results in statistics. Another major theme of his life's endeavours was probability theory. In his Essai philosophique sur les probabilités (1814), Laplace set out a mathematical system of inductive reasoning based on probability, which we would today recognise as Bayesian.

He also made seminal contributions to our understanding of the energetics of the oceans with his tidal equations. Here he used the principles of momentum and conservation of energy to describe the energy associated with the motion and dissipation of tides.

Laplace in 1816 was the first to point out that the speed of sound in air depends on the heat capacity ratio. Newton's original theory gave too low a value, because it does not take account of the adiabatic compression of the air which results in a local rise in temperature and pressure. Laplace's investigations in practical physics were confined to those carried on by him jointly with Lavoisier in the years 1782 to 1784 on the specific heat of various bodies.

Jean D’Alembert was one of his academic advisors and Simeon Poisson his doctoral student.

Sources

• Cleveland, Cutler (Lead Author); Peter Saundry (Topic Editor). 2008. "Laplace, Pierre-Simon." In: Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). [First published in the Encyclopedia of Earth September 15, 2006; Last revised August 21, 2008; Retrieved February 27, 2009]. 
• Wikipedia Contributors, Pierre-Simon Laplace, Wikipedia The Free Encyclopedia, Accessed 27 February 2009.