Arnold Sommerfeld

Born Dec. 5, 1868, in Königsberg; died Apr. 26, 1951, in Munich. German physicist and mathematician.

Sommerfeld graduated from the University of Königsberg in 1891. He was a professor of mathematics at the Clausthal Mining Academy from 1897, at the Technische Hochschule in Aachen from 1900, and at the University of Munich from 1906. His most important works were on atomic theory, the theory of metals, and mathematical physics. He perfected the Bohr model of the atom, proposing a more general formulation of the quantum conditions that permitted not only circular but also elliptical orbits. Consideration of the dependence of mass on velocity made it possible to formulate the theory of the fine structure of hydrogen-like atoms (1916). Applying the Pauli exclusion principle to the electron gas in metals, Sommerfeld gave a more accurate formula for the Wiedemann-Franz law and explained a number of phenomena in metals—Joule heat, thermoelectric effects, and so forth (1928). He created a rigorous mathematical theory of diffraction (1895), obtained an integral representation of Bessel functions (the Sommerfeld integral; 1896), solved the problem of the radiation of a vertical dipole placed on the boundary between two media (1909), made a substantial contribution in the study of X rays, and worked out a theory of bremsstrahlung of electrons (1931).