Jaume Navarro

Electron diffraction chez Thomson : early responses to quantum physics in Britain

In 1927, George Paget Thomson, professor at the University of Aberdeen, obtained photographs that he interpreted as evidence for electron diffraction. These photographs were in total agreement with de Broglies principle of wave-particle duality, a basic tenet of the new quantum wave mechanics. His experiments were an initially unforeseen spin-off from a project he had started in Cambridge with his father, Joseph John Thomson, on the study of positive rays. This paper addresses the scientific relationship between the Thomsons, father and son, as well as the influence that the institutional milieu of Cambridge had on the early work of the latter. Both Thomsons were trained in the pedagogical tradition of classical physics in the Cambridge Mathematical Tripos, and this certainly influenced their understanding of quantum physics and early quantum mechanics. In this paper, I analyse the responses of both father and son to the photographs of electron diffraction: a confirmation of the existence of the ether in the former, and a partial embrace of some ideas of the new quantum mechanics in the latter.

Boundaries Between Territories of Knowledge

In this paper, I argue that scientific disciplines are not natural kinds; rather their boundaries and limits are the result of contingent, historical processes. In his inductive philosophy, the Cambridge-based, influential polymath William Whewell depicted scientific fields as each referring to one definite object, based on one particular principle and largely independent from the rest of disciplines. This static portrait of the division of science contrasts with the history of the configuration of disciplines in the old English university during the second half of the nineteenth century. Taking the career of the physicist Joseph John Thomson as a case study, I describe the process by which physics became institutionally distinct from chemistry, in spite of his constant attempts to create a large department for what he called the “physical sciences”, which would include physics, chemistry and engineering. Moreover, his interest in spiritualism strengthened his views on the unity of all science and the continuity between different “provinces of knowledge”. Interestingly, this unity was instrumental in his work on electrical discharge in gases and the eventual discovery of the electron. Thus, I argue that the boundaries between disciplines should be readily transgressed, following the circulation of knowledge, methods and principles before such boundaries actually crystallized.

A Peripheral Centre. Early Quantum Physics at Cambridge

The history of quantum physics and early quantum mechanics took place mainly in Germany and Copenhagen. British institutions were slow in understanding and accepting the radical transformations involved in the new theory. In this paper I discuss the ways in which quantum physics was slowly incorporated in the University of Cambridge, with an emphasis on the pedagogical and research practices in the old university. For an older generation, the problem with quantum theory was its distance from what true physics was and had to be: a set of mechanical and dynamical models grounded on the mathematics of the continuum. A first generation of converts to the new theory, like Charles Galton Darwin, were quick to incorporate the new theory in the Cambridge syllabus, but only in continuity with the old mathematical tools. As a consequence, wave mechanics a la Schrodinger was easier to accept than the new formalisms of matrix mechanics. It was only with the work of Paul A. M. Dirac, whose initial training and career took place outside Cambridge, that the old university finally regained its relevance at the forefront of quantum theoretical physics.