The Concept of Particle Creation before and after Quantum Mechanics

Abstract

One of the most important results in the recent development of electron theory, Victor Weisskopf wrote in the mid-thirties, the possibility of transforming electromagnetic field energy into matter. A light quantum, for example, in the presence of other electromag netic fields in empty space, can be absorbed and transformed into matter, with the creation of a pair of electrons with opposite charge.1 By recent, Weisskopf meant the period since P. A. M. Dirac's theory of the electron, which was published in 1928.2 Today, physicists by and large still believe that the concept of the creation of fundamental particles, as well as that of the inverse process of their destruction, is a product of quantum mechanics. In actuality, creation and annihilation concepts antedate quantum mechanics. The concept of the annihilation of pairs of oppositely charged, elementary particles,3 for example, dates from the turn of the twentieth century. It became important in astrophysics about 1924, and continued to be through the early thirties. The annihilat ing pairs were first positive and negative electrons, later protons and electrons, and finally, starting in 1931, electrons and anti-electrons. For the physicists who were building quantum mechanics, the concept was familiar and acceptable, if minor, and they included it in their theories where convenient. In Dirac's hole theory of 1930, for example, pair annihilation was neither novel nor central. Dirac's object was to deal with a difficulty inhering in relativistic electron