In his Gifford Lecture, delivered at the University of St. Andrews in the winter-semester 1955/56, Heisenberg declared: “Within the field of modern physics the theory of relativity has played a very important role. It was in this theory that the necessity for a change in the fundamental principles of physics was recognized for the first time.”(8)Really? The greatest idea in physics of a century ago was an assumption with no physical meaning, according to Born? There are some who argue that Einstein's genius was to apply pure thought to propose untestable ideas.
A similar statement had been made by Heisenberg already in 1934 when he declared: “The fundamental presuppositions of classical physics, which led to the scientific picture of the 19th century, had been challenged for the first time by Einstein’s special relativity.”(9) Specifying exactly the premise of classical physics which gave rise to this challenge, Heisenberg continued: “It was the assumption that it is meaningful without further consideration to call two events simultaneous in the case they do not occur at the same place.”
Heisenberg’s statement, that Einstein’s 1905 analysis of the notion of simultaneity and of the concept of time, which — as we shall see later on — Einstein based on the notion of simultaneity, inaugurated the mod-ern physical world picture can be confirmed by the fact that already in 1907 Einstein himself admitted: “It turned out, surprisingly, that it was only necessary to provide a sufficiently precise formulation of the notion of time in order to resolve the difficulty encountered.” (10) Also later, in an impromptu talk, entitled “How I created the theory of relativity,” deliv-ered at Kyoto University on December 14, 1922, Einstein reportedly gave the following account: “Why do the two concepts [i.e., the relativity pos-tulate and the light postulate] contradict each other? I realized that this difficulty was really hard to overcome. I spent almost a year in vain to resolve this problem... Suddenly I understood where the key to this prob-lem lay... An analysis of the concept of time was my solution. Time can-not be absolutely defined, and there is an inseparable relation between time and signal velocity. With this new concept I could resolve all the diffi-culties completely for the first time. Within 5 weeks the special theory of relativity was completed.” (11) ...
Fifty years ago nearly a hundred physicists from all over the world celebrated the 50th anniversary of the theory of relativity in a congress that convened in Bern, where Einstein had written his 1905 relativity paper. At the concluding festive meeting the final lecture was delivered by Max Born who at the end of his talk declared: “Einstein’s leading princi-ple was simply that something of which you could think and form a con-cept, but which from its very nature could not be submitted to an experi-mental test, like the simultaneity of events at distant places, has no phys-ical meaning.” (62) [Jammer, Max, “The Strange Story of the Concept which Inaugurated Modern Theoretical Physics,” Foundations of Physics 34, No. 11 (November 2004), 1617-1641.]
You can read about Poincaré–Einstein synchronisation. It was a good idea, but not original to Einstein. There is some dispute about how he learned it. Alberto A. Martínez writes:
Specifically, he complains that I follow Einstein’s account of how clocks synchronized by out-and-back light signals require a convention: the assumption that the speeds of light in opposite directions are equal. Ohanian claims that “Einstein took this procedure from Poincaré’s Science and Hypothesis.” But Ohanian’s claim is mistaken. Ohanian footnotes the English translation (1905) of Poincaré’s book. The problem is that Einstein did not read English at all. As I explained in my book, Einstein read either the original French edition of Poincaré’s book (1902), or its German translation (1904), and neither of these editions says anything about how to synchronize clocks using out-and-back light signals. Ohanian’s confusion arises because he did not use primary sources, he just looked at the English translation which includes an Appendix: Poincaré’s article on “The Principles of Mathematical Physics,” which was absent in the original editions of the book because it was a later address which he presented to the International Congress of Arts and Science in St. Louis, in 1904. Notwithstanding Ohanian’s confusion, we just don’t know where Einstein learned the procedure he described for synchronizing clocks. As I show in my Kinematics, it is conceivable that Einstein learned it from a paper by Poincaré from 1900, which we know Einstein had read by 1906, or perhaps from someone who had read it, or perhaps from Poincaré’s book, which was published in 1905 (Einstein read it in 1905, but we do not know if he read it before writing his first paper on relativity), or perhaps from another source; we just don’t know.Yes, that is right. Einstein wrote an account in 1949 of how he discovered relativity, and he did not even mention Poincare. When asked about Poincare, he was evasive.