December 14, 1900: Max Planck presents the Quantum Theory at the Physics Society in Berlin.

On December 14, 1900, MAX PLANCK presented his derivation of the distribution law for black-body radiation to the German Physical Society, and the concept of energy quanta made its first appearance in Physics. Considering the enormous consequences which the quantum theory has had, it is astonishing that so little attention has been devoted to detailed study of the reasoning which brought PLANCK to the first radical step of introducing quanta. There are, of course, many descriptions of the origin of the quantum theory in the literature, but almost all of them are historically inaccurate, uncritical, and quite misleading as to both PLANCK’S own work and the context in which it was done.

We do have PLANCKS retrospective accounts which give a clear and consistent
picture of his own view of the development, and there is also an excellent monograph by ROSENFELD, too little known, on the early years of the quantum
theory, which presents PLANCK’S work in its proper historical setting.
It seems to me that there are still two critical questions, not unrelated, which
must be answered, if we are to understand fully the nature of PLANCK’S decisive
step and the extent to which it marked a real break with previous thinking.

The first is really an historical question: Was PLANCK aware of the radiation
distribution law which RAYLEIGH had derived as a necessary consequence of classical
Physics? Most authors answer this question in the affirmative and describe
PLANCK’S introduction of quanta as his response to the challenge of the “crisis”
brought about by the disagreement between classical theory and experimental
results and by the internal failure of classical theory as expressed in the “ultraviolet catastrophe”. As a matter of fact, there was no such crisis, or perhaps one should say there was no awareness of such a crisis. All of the work on blackbody radiation prior to the summer of 1900 was done without benefit of the knowledge of just what classical physics did imply for this problem. It was only in June, 1900 that Lord RAYLEIGH published a two-page note in which the classical distribution law was first derived, and the very serious implications of RAYLEIGH’S paper were not generally realized for quite some time.

PLANCK makes no reference to RAYLEIGH’S note in his own papers of 1900 and 1901, nor does he refer to RAYLEIGH in his accounts of the origins of the quantum theory published many years later. It does, however, seem likely that PLANCK knew of RAYLEIGH’S work, but that he attached no more significance to it than he did to several other papers, published at about the same time, in which more or less ad hoc attempts were made to find an equation which would describe the experimental results.

The possible reasons for PLANCK’S neglect of what now seems to be the critically
important contribution made by RAYLEIGH are to be sought in PLANCK’S background, in his way of approaching the radiation problem, and also in the manner
in which RAYLEIGH had communicated his results.