Summary: Notes on the lecture which Paul A. M. Dirac presented at the University of Cambridge. The lecture discusses the Bohr-Summerfeld theory, the Heisenberg principle, and Dirac's own equation.
Although Dirac rarely participated in the interpretational debates over quantum theory, it is traditionally assumed that his views were aligned with Heisenberg and Bohr in the so-called Copenhagen-Göttingen camp. However, an unpublished—and apparently unknown—lecture of Dirac's reveals that this view is mistaken; in the famous debate between Einstein and Bohr, Dirac sided with Einstein. Surprisingly, Dirac believed that quantum mechanics was not complete, that the uncertainty principle would not survive in the future physics, and that a deterministic description of the microworld would be recovered. In this paper I show how we can make sense of this unpublished lecture in the context of Dirac's broader philosophy of quantum mechanics, and how our present understanding of Dirac's philosophical views must be revised.
‘The light dawns’ describes the period in 1925 and 1926 when modern quantum theory became fully fledged. German theorist Werner Heisenberg, working on spectroscopy, developed matrix mechanics. At the same time, Prince Louis de Broglie and then Erwin Schrödinger developed a second account of quantum theory — wave mechanics. The Schrödinger equation is the fundamental dynamical equation of quantum theory. Paul Dirac, in Cambridge, set out the general principles in his Principles of Quantum Mechanics, published in 1930. The superposition principle and double slits experiment are described and probabilities, observables, and the uncertainty principle explained. Finally, Niels Bohr's idea of complementarity and quantum logic are discussed.