Rupture et continuité dans la physique française : Henri Poincaré et les fondements mécaniques de la thermodynamique

Abstract

After 1850, Laplacian or Amperean molecular physics found itself in competition with other approaches involving thermodynamics and kinetic theories. Henri Poincaré is one of the very few French scientists to have made a significant contribution to the development of classical statistical mechanics at the turn of the century. His openness to foreign physics, a pluralist perspective and the physics of principles marked a break with the alleged self- sufficiency of French physics. However, the evolution of Poincaré’s ideas on mechanical reductionism cannot be fully understood without referring to the Laplacian cosmovision which remained alive around 1880 despite the ambient positivism or descriptionism. Poincaré’s contribution has its roots in French physicists’ long-standing thematic commitment even though he was also open to the Maxwell’s ideas and also integrated celestial mechanics. In his lectures on thermodynamics (1888–1889), Poincaré was first interested in the non-probabilistic mechanical analogies proposed by Helmholtz for the principles of thermodynamics which were in harmony with this cosmovision. Around 1893, he adopted Boltzmann and Maxwell’s ideas, establishing a relationship between results from celestial mechanics (recurrence, non-uniform integrals) and the foundations of classical statistical mechanics. He developed a growing interest in the explanation of irreversibility in this framework.