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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).

The Columbia Electronic Encyclopedia Copyright © 2004.

Licensed from Columbia University Press

Licensed from Columbia University Press

(born Aug. 8, 1902, Bristol, Gloucestershire, Eng.—died Oct. 20, 1984, Tallahassee, Fla., U.S.) English mathematician and theoretical physicist. His first major contribution (1925–26) was a general and logically simple form of quantum mechanics. About the same time, he developed ideas of Enrico Fermi, which led to the Fermi-Dirac statistics. He then applied Albert Einstein's special theory of relativity to the quantum mechanics of the electron and showed that the electron must have spin of

Learn more about Dirac, P(aul) A(drien) M(aurice) with a free trial on Britannica.com.

Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.

In quantum mechanics, one of two possible ways (the other being Bose-Einstein statistics) in which a system of indistinguishable particles can be distributed among a set of energy states. Each available discrete state can be occupied by only one particle. This exclusiveness accounts for the structure of atoms, in which electrons remain in separate states rather than collapsing into a common state. It also accounts for some aspects of electrical conductivity. This theory of statistical behaviour was developed first by Enrico Fermi and then by P.A.M. Dirac (1926–27). The statistics apply only to particles such as electrons that have half-integer values of spin; the particles are called fermions.

Learn more about Fermi-Dirac statistics with a free trial on Britannica.com.

Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.

(born Aug. 8, 1902, Bristol, Gloucestershire, Eng.—died Oct. 20, 1984, Tallahassee, Fla., U.S.) English mathematician and theoretical physicist. His first major contribution (1925–26) was a general and logically simple form of quantum mechanics. About the same time, he developed ideas of Enrico Fermi, which led to the Fermi-Dirac statistics. He then applied Albert Einstein's special theory of relativity to the quantum mechanics of the electron and showed that the electron must have spin of

Learn more about Dirac, P(aul) A(drien) M(aurice) with a free trial on Britannica.com.

Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.

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

- 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.
- 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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Last updated on Friday January 05, 2007 at 13:26:43 PST (GMT -0800)

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