Dirac, Paul Adrien Maurice (born 8.08.1902) is an English theoretical physicist, one of the creators of quantum mechanics, and a Fellow of the Royal Society (1930). Born in Bristol. Graduated from Bristol (1921) and Cambridge (1926) universities. In 1932–68 he was professor at the University of Cambridge.
His work was in the field of quantum mechanics, quantum electrodynamics, quantum field theory, the theory of elementary particles and the theory of gravitation. He developed (1926–27) the mathematical apparatus of quantum mechanics — the transformation theory — and proposed (1927) the method of second quantisation. In 1927 he applied the principles of quantum theory to the electromagnetic field and obtained the first model of a quantised field, thereby founding quantum electrodynamics. He predicted the identity of the quanta of stimulated and of primary radiation, which underlies quantum electronics (1927). With W. Heisenberg he discovered the exchange interaction in 1928, introducing exchange forces.
In 1928 he constructed a relativistic theory of the motion of the electron, proposing a wave equation which describes the motion of the electron and satisfies relativistic invariance (relativistic quantum mechanics). Dirac's theory brings harmoniously together relativity, quanta and spin, which until then had seemed independent notions. An important conclusion followed from Dirac's theory, that the electron can have negative values of energy. On this basis he assumed the existence of a positively charged electron, or positron, which was discovered in 1932. He constructed the theory of holes (1930), and in 1931 predicted the existence of antiparticles and the creation and annihilation of electron–positron pairs. In 1931 he put forward the hypothesis of the existence of an elementary magnetic charge (the Dirac monopole), and in 1933 that of antimatter. He postulated the effect of vacuum polarisation (1933). For the creation of quantum mechanics he was awarded the Nobel Prize in 1933 together with E. Schrödinger.
Independently of E. Fermi he developed in 1926 the statistics of particles with half-integer spin (Fermi–Dirac statistics). In 1931 he argued for the possible existence of a symmetric quantum electrodynamics based on elementary magnetic charges. In 1932, together with V. A. Fock and B. Podolsky, he proposed the many-time formalism — the direct predecessor of modern quantum electrodynamics. In 1936 he constructed a general theory of classical fields, chiefly for free particles.
He advanced (1937) the hypothesis that gravitation changes with time. In 1942 he introduced the notion of an indefinite metric in order to remove the infinite self-energy of the electron. In 1962 he developed a theory of the muon in which the muon is described as an oscillatory state of the electron. In recent years he has been working on the problem of a Hamiltonian formulation of the theory of gravitation with a view to the further quantisation of the gravitational field.
An honorary member of a number of academies of sciences and scientific societies, and a foreign member of the USSR Academy of Sciences (1931). The Royal Medal (1939), the Copley Medal (1952), the R. Oppenheimer Prize and others.