24
Einstein as aTransitionalFigure:
The Birth of Wave Mechanics
We now leave the period of the old quantum theory and turn to the time of tran-
sition, during which matter waves were being discussed by a tiny group of phys-
icists 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 [Bl, B2]. It ends in January 1926
with Schroedinger's first paper on wave mechanics [SI]. 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 fundamen-
tal development that preceded Schroedinger's discovery of wave mechanics: the
discovery of matrix mechanics by Heisenberg [HI]. Therefore, I shall have no
occasion in this book to comment in any detail on Heisenberg's major
achievements.
24a. From Einstein to de Broglie
During the period that began with Einstein's work on needle rays (1917) and
ended with Debye's and Gompton'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
"The other ones I know of are Brillouin [B3], Wolfke [Wl], Bothe [B4], Bateman [B5], and Orn-
stein and Zernike [Ol].
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