Sommerfeld, Arnold Johannes Wilhelm (1868–1951)

German physicist who demonstrated that difficulties with Niels Bohr's model of the atom, in which electrons move around a central nucleus in circular orbits, could be overcome by supposing that electrons adopt elliptical orbits.

This led him in 1916 to predict a series of spectral lines based on the relativistic effects that would occur with elliptical orbits. Friedrich Paschen (1865–1945) undertook the spectroscopic work required and confirmed Sommerfeld's predictions.

Sommerfeld was born and educated in Königsberg, Prussia (now Kaliningrad, Russia). He was professor at the Mining Academy in Clausthal 1897–1900, at the Technical Institute in Aachen 1900–06, and then moved to Munich University as director of the Institute of Theoretical Physics, specially established for him. Sommerfeld built his institute into a leading centre of physics.

Sommerfeld was active as a theoretician both in physics and engineering, and he produced a four-volume work on the theory of gyroscopes 1897–1910 with mathematician Felix Klein. Sommerfeld's other works include Atombau und Spektrallinien/Atomic Structure and Spectral Lines 1919 and Wellenmechanischer Ergänzungsband/Wave Mechanics 1929.