Pierre Simon Laplace, 1749-1827: A Determined Scientist ,
When Pierre Simon Laplace died on 5 March 1827, his eulogists had difficulty finding matters of human interest to lighten the life story of France’s most illustrious mathematician. Born in Normandy to a family of prosperous farmers, Laplace impressed many during his childhood with his skill in mathematics, yet he prepared for a life in the Catholic Church. His professors at the University of Caen recognized his mathematical ability, but it took nerve for the 20-year-old to forsake a secure religious career and travel to Paris with the hopes of making a livelihood as a scientist. Fortunately, Laplace was able to impress Jean d’Alembert, the reigning mathematician at the Paris Academy of Sciences, who took the young man under his wing and obtained a teaching position for him at the École Militaire.
Cut off from family and the church, Laplace was on his own. He knew that admission to the Paris Academy of Sciences was essential for future success. He produced 13 mathematical papers in 3 years and gained admission to the academy in 1773, beating out older, better-established mathematicians in the process. In the next 4 years he produced 20 more papers, and he didn’t slow down until he reached age 75. Evidently, the eulogists’ frustration came from the fact that Laplace never had time to do anything interesting except work.
In Pierre Simon Laplace, 1749–1827: A Determined Scientist, Roger Hahn does not attempt a technical account of Laplace’s work. For that he refers readers to the lengthy entry on Laplace in the Dictionary of Scientific Biography (Scribner, 1970–80), edited by Charles C. Gillispie. Hahn provides new insight into Laplace’s religious and philosophical reflections. Laplace was willing to tell Napoleon that there was no need for the “hypothesis” of a God in science, so one might expect him to have had little interest in religion and philosophy. However, Laplace’s popular writings, such as his 1796 Exposition du système du monde (Exposition of the World System) and his Essai philosophique sur les probabilités (Philosophical Essay on Probability), published in 1814, reveal a penchant for philosophical speculation.
Hahn, who has studied Laplace for many years, had access to new non-scientific manuscripts that demonstrate Laplace’s early religious concerns and allowed Hahn to flesh out this part of Laplace’s life. Hahn concludes that once Laplace abandoned the church for science, his philosophy remained remarkably consistent throughout his life. Laplace was convinced that all events were determined by the laws of nature and that even the science of probability was merely a sign of our ignorance of those certain laws. Hahn does a better job than Laplace’s previous biographers in showing the context of Laplace’s commitment to determinism.
Perhaps Laplace’s constant labor explains how he survived the French Revolution, the Napoleonic era, and the restoration of the monarchy while heads rolled around him. His close associates, the Marquis de Condorcet, Antoine Lavoisier, and Jean Sylvain Bailly, all died during the Reign of Terror—but not Laplace. After the coup of 18 brumaire (9 November 1799), Napoleon Bonaparte made Laplace minister of the interior and appointed him to the senate. Earlier in 1784, Laplace had become an examiner of the Royal Artillery Corps; in 1785 he inspected and passed the young Napoleon, thereby confirming his military career. After Napoleon was exiled to Elba, it was Laplace, the leading member of the senate, who welcomed Louis XVIII to Paris. His detractors called him a “weathercock,” always turning with the wind; his supporters described him as the ideal public servant, indispensable to anyone in power.
Laplace’s greatest works, Traité de mécanique céleste ( Celestial Mechanics ), published between 1798 and 1825, and the 1812 Théorie analytique des probabilités (Analytical Theory of Probability), reveal a powerful mind concentrating on mathematical applications. He had little interest in pure mathematics. His emphasis on the applied might explain his collaboration with Lavoisier on the study of heat and chemical combustion, which was an opportunity for Laplace in several ways. Laplace gained access to the best-equipped laboratory in the world, although it meant sacrificing time from his beloved mathematical work. Lavoisier’s great wealth also helped Laplace’s father through an embarrassing financial predicament. And Laplace’s later studies of sound, light, and capillary action stem from his commitment to applied mathematics and to his laboratory work with Lavoisier.
It is doubtful that Laplace ever returned to the piety of his youth, although some accounts of his death suggest that he might have been inclined in that direction. Pierre Simon Laplace, 1749–1827 first appeared in French as Le système du monde: Pierre Simon Laplace, un itinéraire dans la science (Gallimard, 2004). The author has translated and slightly amended the original, and has added appendices. The biography will be gratefully received by everyone interested in this major figure in the history of mathematics and physics.