Arnold Johannes Wilhelm Sommerfeld (December 5, 1868 – April 26, 1951) was a German physicist who introduced the fine-structure constant in 1919.

Arnold Sommerfeld was born in Königsberg where he studied mathematics and physical sciences at its university. After receiving his doctorate in 1891 he changed to the University of Göttingen, where he received a professorship in 1896. He became professor of mathematics at the University of Clausthal-Zellerfeld in 1897 and of technical engineering at the University of Aachen in 1900, where he developed the theory of Hydrodynamic lubrication. In 1897, he began a thirteen-year collaboration with C.F. Klein on a four-volume treatise of the gyroscope.

From 1906-1931 he established himself as professor of physics at the University of Munich. There he came in contact with the special theory of relativity by Albert Einstein, which was not yet widely accepted at that time. His mathematical contributions to the theory helped its acceptance by the skeptics. In 1914 he studied with Léon Brillouin the propagation of electromagnetic waves in dispersive media. Later he became one of the founders of quantum mechanics; he codiscovered the Sommerfeld-Wilson quantization rules, a generalization of Bohr's atomic model that was eventually superseded by the Schrödinger equation. His Atomic Structure and Spectral Lines (1919) became a classic. Many of his students, most notably Werner Heisenberg, Wolfgang Pauli, Hans Bethe and Peter Debye, became famous in their own right.

In 1927 Sommerfeld applied Fermi-Dirac statistics to the Drude model of electrons in metals. The new theory solved many of the problems predicting thermal properties that model had.

Sommerfeld was a great theoretician, and besides his invaluable contributions to the quantum theory, he worked in other fields of physics, such as the classical theory of electromagnetism. For example, he proposed a solution to the problem of a radiating hertzian dipole over a conducting earth, which over the years led to many applications. His Sommerfeld identity and Sommerfeld integrals are still to the present day the most common way to solve this kind of problem.

He was awarded the Lorentz Medal in 1939.

Sommerfeld died in 1951 in Munich from injuries after a traffic accident.

Links

• John J. O'Connor and Edmund F. Robertson. Arnold Sommerfeld Biography at the MacTutor archive .
  
• Relativitätstheorie — Sommerfeld's 1921 introduction to special and general relativity for general audiences (German)
  
• Arnold Sommerfeld - the supporter of Indian physics in Germany