CfA Colloquium Schedule Fall 2008
 25 September 2008

25 September 2008

Speaker: James Evans (Program in Science, Technology and Society, University of Puget Sound)

Title: Gravity in the Century of Light: The Gravitation Theory of Georges-Louis Le Sage

Abstract: Each generation of physicists, or natural philosophers, has sought to place universal gravitation in the context of its own worldview. Often this has entailed an effort to reduce gravity to something more fundamental. But what is deemed fundamental has, of course, changed with time. Each generation attacked the problem of universal gravitation with the tools of its day and brought to bear the concepts of its own standard model. The most successful eighteenth-century attempt to provide a mechanical explanation of gravity was that of Georges-Louis Le Sage (1724-1803) of Geneva. Le Sage imagined a sea of ultramundane corpuscles, streaming in all directions and characterized by minute mass, great velocity, and complete inelasticity. Mostly these corpuscles just pass through large bodies such as apples or planets, but a few are absorbed, leading to all the phenomena of attraction. Le Sage's theory is an especially interesting one, for several reasons. First, it serves as the prototype of a dynamical explanation of Newtonian gravity. Second, the theory came quite close to accomplishing its aim. Third, the theory had a long life and attracted comment by the leading physical thinkers of several successive generations, including Laplace, Kelvin, Maxwell and Feynman. Le Sage's theory therefore provides an excellent opportunity for the study of the evolution of attitudes toward physical explanation. The effects of national style in science and generational change take on a new clarity.

Video of the Presentation (Talks can be viewed with RealPlayer. Free download is available from )


Section Photo