Dirac, P.A.M.; On the Theory of Quantum Mechanics
Proc. Roy. Soc. A112 (1926) 661;
The present theory is shown to account for the absorption and stimulated emission of radiation, and also shows that the elements of the matrices representing the total polarization determine the transition probabilities. One cannot take spontaneous emission into account without a more elaborate theory involving the positions of the various atoms and the interference of their individual emissions, as the effects will depend upon whether the atoms are distributed at random, or arranged in a crystal
lattice, or all confined in a volume small compared with a wave-length. The last alternative mentioned, which is of no practical interest, appears to be the simplest theoretically. It should be observed that we get the simple Einstein results only because we have averaged over all initial phases of the atoms. (Science Abstracts, 1927, 294. G. W. de T.).
Rediscovery of statistics for an ensemble of fermions - the Fermi-Dirac quantum statistics.