Quantization of the electromagnetic field, entropy of an ideal monoatomic gas, and the birth of Bose-Einstein statistics

In 1924, Einstein received a short manuscript in the mail from the Indian physicist S.N. Bose. He quickly translated Bose’s manuscript to German and submitted it to Zeitschrift für Physik. Within a few weeks, Einstein presented his own findings (using a generalization of Bose’s counting method) to a session of the Prussian Academy of Sciences. Whereas Bose had suggested a new counting method for the quanta of the electromagnetic field – one that yielded Planck’s blackbody radiation formula – Einstein applied Bose’s method to an ideal monoatomic gas. Shortly afterward, Einstein presented to the Academy a follow-up paper in which he described the Bose-Einstein condensation for the first time. The present paper describes some of the fascinating issues that Einstein struggled with as he attempted to unify the quantum-statistical properties of matter with those of the electromagnetic field.