Einstein as a Transitional Figure: The Birth of Wave Mechanics
We now leave the period of the old quantum theory and turn to the time of transition, during which matter waves were being discussed by a tiny group of physicists at a time when matter wave mechanics had not yet been discovered. This period begins in September 1923 with two brief communications by Louis de Broglie to the French Academy of Sciences [B1, B2]. It ends in January 1926 with Schroedinger's first paper on wave mechanics [S1]. The main purpose of this chapter is to stress Einstein's key role in these developments, his influence on de Broglie, de Broglie's subsequent influence on him, and, finally, the influence of both on Schroedinger.
Neither directly nor indirectly did Einstein contribute to an equally fundamental development that preceded Schroedinger's discovery of wave mechanics: the discovery of matrix mechanics by Heisenberg [H1]. Therefore, I shall have no occasion in this book to comment in any detail on Heisenberg's major achievements.
During the period that began with Einstein's work on needle rays ( 1917) and ended with Debye's and Compton's papers on the Compton effect ( 1923), there were a few other theoreticians also doing research on photon questions. Of those, the only one* whose contribution lasted was de Broglie.
De Broglie had finished his studies before the First World War. In 1919, after a long tour of duty with the French forces, he joined the physics laboratory headed by his brother Maurice, where X-ray photoeffects and X-ray spectroscopy were the main topics of study. Thus he was much exposed to questions concerning the nature of electromagnetic radiation, a subject on which he published several papers. In one of these [B6], de Broglie evaluated independently of Bose (and____________________