A Theory of Electrons and Protons. Offprint from Proceedings of the Royal Society, Series A, Vol. 126, No. A801

DIRAC, Paul

Edité par Harrison & Sons for the Royal Society, London, 1930

A propos de cet article

ANTIMATTER. First edition, extremely rare offprint, of Dirac's prediction of antimatter - although he did not accept it as such until a year later (see below) - and the advent of the dynamical view of the vacuum which was fundamental to the later development of quantum field theory. "The consensus among today's scientists is that Dirac's role in foreseeing the existence of the positron is one of the greatest achievements in science. In 2002, shortly after the centenary of Dirac's birth, the theoretical physicist Kurt Gottfried went further: 'Physics has produced other far-fetched predictions that have subsequently been confirmed by experiment. But Dirac's prediction of anti-matter stands alone in being motivated solely by faith in pure theory, without any hint from data, and yet revealing a deep and universal property of nature'" (Farmelo, p. 226). One troubling consequence of the famous Dirac relativistic wave equation was that it implied that electrons should exist in states of negative as well as positive energy. Therefore a Dirac electron with initially positive energy should fall indefinitely by spontaneous emission towards states of lower and lower energy. To avoid this Dirac postulated in 'A Theory of Electrons and Protons' that the states of negative energy were normally filled up - electrons could not then fall into them because the Pauli exclusion principle prevents two electrons from occupying the same state. Dirac observed that holes in this 'sea' would behave like positively-charged particles. Dirac initially believed that his holes could be identified with protons, but Hermann Weyl and others showed that they should have the same mass as the electron. The following year, in the introduction to another paper (on a different topic), Dirac conceded and called these holes 'anti-electrons'. The existence of this particle was demonstrated experimentally by Carl Anderson in 1932; he called it the 'positron'. In 1973, Heisenberg said that the proposal of the anti-electron was "perhaps the biggest jump of all big jumps in physics of our century." In Dirac's new picture 'empty space' had become much more complicated. It was no longer empty and in fact behaves in many ways like a semiconductor, where electrons can be excited out of a filled valence band while leaving holes (physicists now call it 'the vacuum'). Dirac shared the 1933 Nobel Prize in Physics with Schrödinger for "for the discovery of new productive forms of atomic theory." OCLC lists only the copy at the University of Florida, where Dirac spent his final years and where many of his papers are held. No copies in auction records. In 1928, Dirac published his discovery of the 'Dirac equation', his relativistic wave equation for the electron, which "ranks among the highest achievements of twentieth-century science" (Pais, p. 290). However, "it was clear to Dirac and several of his colleagues that the relativistic electron theory of 1928 led to strange consequences. The problem, sometimes referred to as the '± difficulty,' had its basis in the Dirac equation, which formally included solutions with negative energy. Contrary to the situation in classical physics, these could not be dismissed as nonphysical but had to be taken seriously - that is, somehow to be related to some objects of nature" (Kragh (1999), p. 190). "Dirac's equation consists of four components. That is, it contains four separate wave functions to describe electrons. Two components have an attractive and immediately successful interpretation, describing the two possible directions of an electron's spin. The extra doubling, by contrast, appeared at first to be quite problematic. "In fact, the extra equations contain solutions with negative energy (and either direction of spin). In classical (non-quantum) physics the existence of extra solutions would be embarrassing, but not necessarily catastrophic. For in classical physics, you can simply choose not to use these solutions. This of course begs the.

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Détails bibliographiques

• Titre: A Theory of Electrons and Protons. Offprint from Proceedings of the Royal Society, Series A, Vol. 126, No. A801
• Éditeur: Harrison & Sons for the Royal Society, London
• Date de parution: 1930
• Édition: First edition.
• Catalogues du vendeur:
  • Atomic Physics, Quantum Theory