23
A Loss of Identity:
the Birth of Quantum Statistics
23a. From Boltzmann to Dirac
This episode begins with a letter dated June 1924 [Bl], written by a young Ben-
gali. His name was Satyendra Nath Bose. The five papers he had published by
then were of no particular distinction. The subject of his letter was his sixth paper.
He had sent it to the Philosophical Magazine. A referee had rejected it [B2].
Bose's letter was addressed to Einstein, then forty-five years old and already rec-
ognized as a world figure by his colleagues and by the public at large. In this
chapter I describe what happened in the scientific lives of these two men during
the six months following Einstein's receipt of Bose's letter. For Bose the conse-
quences were momentous. Virtually unknown before, he became a physicist whose
name will always be remembered. For Einstein this period was only an inter-
lude.* He was already deeply engrossed in his search for a unified theory. Such
is the scope of his oeuvre that his discoveries in those six months do not even rank
among his five main contributions, yet they alone would have sufficed for Einstein
to be remembered forever.
Bose's sixth paper deals with a new derivation of Planck's law. Along with his
letter, he had sent Einstein a copy of his manuscript, written in English, and asked
him to arrange for publication in the Zeitschrift fur Physik, if he thought the work
of sufficient merit. Einstein acceded to Bose's request. He personally translated
the paper into German and submitted it, adding as a translator's note: 'In my
opinion, Bose's derivation of the Planck formula constitutes an important advance.
The method used here also yields the quantum theory of the ideal gas, as I shall
discuss elsewhere in more detail.'
The purpose of this chapter is not to discuss the history of quantum statistics
but rather to describe Einstein's contribution to the subject. Nevertheless, I include
a brief outline of Bose's work for numerous reasons. (1) It will give us some insight
into what made Einstein deviate temporarily from his main pursuits. (2) It will
facilitate the account of Einstein's own research on the molecular gas. That work
*In 1925 Einstein said of his work on quantum statistics, 'That's only by the way' [SI].423