Henri Poincare : biography
Poincare and Einstein: likeness and differences in their theories
Albert Einstein, in his first researching works about the relative theory, used literally the same mathematical model as Poincare applied. Those were: transformations of Lorentz, relative formulae of summing speeds and other points. However, as opposed to Poincare’s work, Einstein made a determined conclusion that it was absurdly to apply the concept of ether only for proving impossibility of its finding. He completely got rid of the concept of ether, and did the same for the concepts of absolute movement and absolute time, supporting the concept of ether, which were still used by Poincare. Exactly that theory, as Max Planck offered, was called the relative theory (while Poincare preferred to say subjective or conditional).
All the new effects, which Lorentz and Poincare considered to be dynamic features of ether, had their source from the objective qualities of space and time in Albert Einstein’s relative theory. In other words, they were carried by Einstein form dynamics to kinematics. That was the most important point of difference between Poincare’s and Einstein’s approaches, being disguised by outer likeness in their mathematical models. They understood deep physical (not only mathematical) essence of those models in different ways. Transfer to kinematics allowed Albert Einstein to create a holistic and general theory of space and time, and, in addition to that, to solve problems, which could not be solved before, using his theory. For example, the complicated question about different kinds of mass, dependence of mass on energy, correlation of ”local” and “absolute” time etc. Nowadays the theory is called special relative theory. One more essential difference between positions of Poincare and Einstein consisted of the fact that Lorentz’s reduction of length, growing of inertness with the speed and others relative conclusions were understood by Poincare as absolute effects, while Einstein considered them to be relative, having no physical consequence in its reference frame. The thing which was real physical time in a moving reference frame for Einstein was understood by Poincare as seeming or “temps apparent” and clearly differentiated it from veritable time or “le temps vrai” in French.
Probably, the lack of deep analysis of physical essence of the special relative theory in Poincare’s work was the reason for physicists not to pay the deserved attention to it. Naturally, the broad response that was aroused by the first publication of Albert Einstein’s work was mostly caused by the deep and clear analysis of the basics of the researched physical picture.
The substantiation of the new mechanics was different either. In Einstein’s articles of 1905 the principal of relativity was not affirmed as a conclusion out of dynamic consideration and experiment in the beginning. Instead of that it was put to the fundament of physics as a kinematic axiom (again, for all the phenomena with no exception). Out that axiom and the stability of the speed of light mathematical apparatus of Lorentz-Poincare was received automatically. The refusal of the concept of ether allowed underlining that “motionless” and “mobile” systems of coordinates were absolutely equal in their rights, and when conversing to the “mobile” system of coordinates, the same effects could be received in the “motionless” one.
Einstein, as he afterwards confessed, was not acquainted neither with the latest publications of Poincare (probably he read only the work of 1900, anyway, with no works of 1904), nor with the latest article of Lorentz of 1904, by the time he began working at the relative theory. Albert Einstein, just the same as other authors of the first works devoted to the relative theory (even in France) didn’t refer to the works by Poincare.
“Poincare kept silence”
Soon after Albert Einstein’s works, devoted to the relative theory were published (approximately 1905), Poincare stopped giving his works on the topic for publication. He mentioned neither Albert Einstein’s name, nor the relative theory in any of his works for the last seven years of his life (except one case when Poincare mentioned Einstein’s theory of photo effect). Poincare continued on speculating on qualities of ether and mentioned absolute movement relative to ether.