438 THE QUANTUM THEORYEinstein become aware of de Broglie's work? In particular, when did he receive
de Broglie's thesis from Langevin? Clearly, it would be most interesting to know
what Professor de Broglie might have to say about these questions. Accordingly
I wrote to him. He was kind enough to reply. With his permission, I quote from
his answers.
De Broglie does not believe that Einstein was aware of his three short publi-
cations [Bl, B2, B3] written in 1923. 'Nevertheless, since Einstein would receive
the Comptes Rendus and since he knew French very well, he might have noticed
my articles' [B8]. De Broglie noted further that he had given Langevin the first
typed copy of his thesis early in 1924. 'I am certain that Einstein knew of my
These since the spring of 1924' [B9]. This is what happened. 'When in 1923 I
had written the text of the These de Doctoral which I wanted to present in order
to obtain the Doctorat es Sciences, I had three typed copies made. I handed one
of these to M. Langevin so that he might decide whether this text could be
accepted as a These. M. Langevin, probablement un peu etonne par la nouveaute
de mes idees,* asked me to furnish him with a second typed copy of my These for
transmittal to Einstein. It was then that Einstein declared, after having read my
work, that my ideas seemed quite interesting to him. This made Langevin decide
to accept my work' [B8].
Thus, Einstein was not only one of the three fathers of the quantum theory,
but also the sole godfather of wave mechanics.24c. From de Broglie and Einstein to Schroedinger
Late in 1925, Schroedinger completed an article entitled 'On Einstein's Gas The-
ory' [S2]. It was his last paper prior to his discovery of wave mechanics. Its con-
tents are crucial to an understanding of the genesis of that discovery [K2].
In order to follow Schroedinger's reasoning, it is necessary to recall first a der-
ivation of Planck's formula given by Debye in 1910 [Dl]. Consider a cavity filled
with radiation oscillators in thermal equilibrium. The spectral density is
8irv^2 e(v, 7)/c^3 , where e is the equilibrium energy of a radiation field oscillator with
frequency v. Debye introduced the quantum prescription that the only admissible
energies of the oscillator shall be nhv, n = 0, 1, 2, .... In equilibrium, the nth
energy level is weighted with its Boltzmann factor. Hence ⬠= 'E,nhvyn/T^yn, y
= exp (âhv/kT). This yields Planck's law.**
Now back to Schroedinger. By his own admission, he was not much taken with
the new BE statistics [S2]. Instead, he suggested, why not evade the new statistics
* Probably a bit astonished by the novelty of my ideas.
**This derivation differs from Planck's in that the latter quantized material rather than radiation
oscillators. It differs from Bose's photon gas derivation in that here the energy nhv is interpreted as
the nth state of a single oscillator, not (as was done in Chapter 23) as a state of n particles with
energy hv.