The Curious Copenhagen Interlude

Abstract

The sequence of scientific events described in such detail in the last chapter was bound to have an extraordinary effect on Kramers. The discovery of the Compton effect and its subsequent refinement by the Bothe-Geiger and Compton-Simon experiments, leading to the disproof of Kramers’ favorite theoretical scheme—the BKS theory—affected him deeply. The central intellectual reorientation that these results required was an altogether different attitude and approach to the photon concept. Pauli in a letter to Kramers writes succinctly and unequivocally: “It can now be considered as proven—to every objective physicist—that photons are just as physically real (or as unreal!) as electrons.”³⁰⁶ In spite of Pauli’s admonition, Kramers had a very difficult time incorporating the photon idea into his physical thinking. Thus, even after he knew that the BKS formulation was untenable, he still writes to Born: “I am convinced that a systematic coupling of individual processes is incompatible with wave optics, but one should try to overcome this contradiction in a less naive manner than Einstein often does.”³⁵³ Einstein described these energy- and momentum-conserving processes in terms of photons-and where Kramers grudgingly admitted that energy and momentum were conserved, he did not admit that this implied the reality of photons. Kramers kept on battling against the photon. It will be recalled that several months after matrix mechanics had demonstrated its great power, Kramers, in a postcard to Fowler, reiterated again that in matrix mechanics “not everything is solved, that light quanta are still out.” ³³⁵