Today is the birthday of Henri Poincaré. Physicist know the Poincaré group of translations and Lorentz transformations, and the Poincaré conjecture about the topology of 3-spheres became widely known last year as the one millennium problem that has been its proofed by a reclusive Russian named Perelman.
But the man behind these concepts is probably not as well know as he deserves to be, considering that he contributed enormously to diverse areas of mathematics and physics. He is better known in France, where he was born on April 29, 1854, in Nancy in Lorraine, but beware: If you see a place, or street in France called Poincaré, it is most probably named after his cousin Raymond Poincaré, who was premier minister and president of the French Republic in 1913-1920.
In physics, Henri Poincaré is most famous for his contributions to the three-body problem, and, of course, to the theory of the electron and the special theory of relativity.
Poincaré discussing with Marie Curie at the 1911 Solvay Congress, while Einstein stands behind. (Source: Solvay Congress 1911)
It is not so easy today to form an unbiased opinion of what Poincaré achieved with respect to relativity, and to give a fair tribute to his and Einstein's respective work and results. That's in part because his original papers about the special theory of relativity are not easily available - I had been searching for a long time before finding some scanned copies to have a glimpse in his 1905 paper, "Sur la dynamique de l'electron", Comptes Rendues 140, 1504-8, and his 1906 paper "Sur la dynamique de l'electron", Rendiconti del Circolo matematico di Palermo 21, 129-176.
It seems that although Poincaré stated a version of the principle of relativity, understood the problems involving simultaneity, formulated the group property of the Lorentz transformations, and postulated the invariance of the laws of physics with respect to different inertial frames, he stayed convinced that all this was a consequence of the detailed dynamics of matter in the rest frame of the ether. A good description of the current understanding of this issue by a historian of science is The Mystery of the Einstein Poincaré Connection, by Olivier Darrigol in Isis 95 (2004) 614–626. Alas, his birthday is to short, even using apparent time, to read all these papers, or the book by Galison, Einstein's Clocks, Poincaré's Maps, which discusses all these topics and contains a biographical sketch of Henri Poincaré...
TAGS: Henri Poincaré, physics, relativity