Navarro, Jaume: Planck and de Broglie in the Thomson Family

In an ironical remark made in 1930 about the situation of physics in the previous years Joseph John Thomson stated that “when the waves are taken into account, the classical theory of dynamics gives the requisite distribution of orbit [of the electrons] in the atom, and as far as these go the properties of the atom are not more inconsistent with classical dynamics than are the properties of organ pipes and violin strings, in which, as in the case of the electron, waves have to be accommodated within a certain distance. It is too much to expect even from classical dynamics that it should give the right result when supplied with the wrong material”.
The context of these remarks is the following: in 1927 J.J.’s son, George Paget Thomson, had obtained experimental evidence of the diffraction of cathode rays in the terms predicted by Louis de Broglie and developed by Erwin Schrödinger. These experiments, which were regarded as proof for one of the basic principles of the new quantum mechanics, were used by J.J. to argue in favour of the old classical physics. In his mindset, electron diffraction did not prove the principles on which Schrödinger’s theory was based, but only the results that theory involved. And these results could also be accounted for with a physical theory—i.e., a mechanical theory—in which the electron had an inner structure.
Contrary to the stubbornness of the father, the son’s reaction to his own experiments was to change his views on the validity of the new physics. Trained in the old physics and an advocate for it in the 1920s, G.P. Thomson was no active actor in the development or acceptance of the new quantum mechanics until electron diffraction appeared on stage.
The history of the early developments of quantum mechanics is, among many other things, the history of the clash of two generations, with different metaphysics and with different epistemologies. In this paper I want to explore the responses of J.J. Thomson and G.P. Thomson to Planck’s law and to de Broglie’s principle. I will compare both responses analysing the way in which the experimental evidence for the new physics was interpreted on the basis of ad hoc mechanical models in the case of the father, and in pragmatic and phenomenological terms by the son. The struggles of both father and son to come to terms with the new physics promises to be an interesting case study to understand the spreading of quantum physics far from the centres where it was being developed.

Navarro (Presentation)
Talk Navarro (*.mp4 audio file)
Essay Navarro (Preprint)