Dirac, Paul Adrien Maurice, 1902-84, English physicist. He was educated at the Univ. of Bristol and St. John's College, Cambridge, and became professor of mathematics at Cambridge in 1932. In 1928, Dirac published a version of quantum mechanics that took into account the theory of relativity (see quantum theory). One consequence of his theory was the prediction of negative energy states for the electron, implying the existence of an antiparticle to the electron; this antiparticle, the positron, was discovered in 1932 by C. D. Anderson. Dirac's equation for the motion of a particle is a relativistic modification of the Schrödinger wave equation, the basic equation of quantum mechanics. For their work Dirac and Erwin Schrödinger shared the 1933 Nobel Prize in Physics. Dirac also received the Copley Medal of the Royal Society in 1952 for this and other contributions to the quantum theory, including his formulation (with Enrico Fermi) of the Fermi-Dirac statistics and his work on the quantum theory of electromagnetic radiation. He wrote The Principles of Quantum Mechanics (1930, 4th ed. 1958).

See biographies by H. Kragh (1990) and G. Farmelo (2009).

In graph theory, there are two theorems that are commonly referred to as Dirac's theorem, both named after the mathematician Gabriel Andrew Dirac:

  1. Let G be a k-connected graph. Then for any set of k vertices in G, there exists a cycle in G that passes through all k vertices.
  2. Let G be a graph on n ≥ 3 vertices. If each vertex has degree at least n/2 then G is hamiltonian.

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