Arnold Sommerfeld

Arnold Johannes Wilhelm Sommerfeld (German: [ˈaʁnɔlt ˈzɔmɐˌfɛlt]; 5 December 1868 – 26 April 1951) was a German theoretical physicist who pioneered developments in both atomic and quantum physics, and also educated and mentored many students for the new era of theoretical physics.

Sommerfeld served as doctoral advisor and postdoctoral advisor to seven Nobel Prize winners and supervised at least 30 other famous physicists and chemists.

Sommerfeld introduced the second quantum number, azimuthal quantum number, and the third quantum number, magnetic quantum number. He also introduced the fine-structure constant and pioneered X-ray wave theory.

Arnold Johannes Wilhelm Sommerfeld was born on 5 December 1868 in Königsberg (now Kaliningrad, Russia) into a family with deep ancestral roots in Prussia. His mother, Cäcilie Matthias (1839–1902), was the daughter of a Potsdam builder. His father, Franz Sommerfeld (1820–1906), was a physician from a leading family in Königsberg, where Arnold's grandfather had resettled from the hinterland in 1822 for a career as Court Postal Secretary in the service of the Kingdom of Prussia. Sommerfeld was baptized a Christian in his family's Prussian Evangelical Protestant Church, and although not religious, he would never renounce his Christian faith.

Sommerfeld studied mathematics and physical sciences at the University of Königsberg. His thesis advisor was the mathematician Ferdinand von Lindemann, and he also benefited from classes with mathematicians Adolf Hurwitz and David Hilbert and physicist Emil Wiechert. His participation in the student fraternity Burschenschaft resulted in a dueling scar on his face. He received his Ph.D. on 24 October 1891.

After receiving his doctorate, Sommerfeld remained at Königsberg to work on his teaching diploma. He passed the national exam in 1892 and then began a year of military service, which was done with the reserve regiment in Königsberg. He completed his obligatory military service in September 1893, and for the next eight years continued voluntary eight-week military service. With his turned up moustache, his physical build, his Prussian bearing, and the fencing scar on his face, he gave the impression of being a colonel in the hussars.

In October 1893, Sommerfeld went to the University of Göttingen, which was the center of mathematics in Germany. There, he became an assistant to Theodor Liebisch at the Mineralogical Institute, through a fortunate personal contact—Liebisch had been a professor at the University of Königsberg and a friend of the Sommerfeld family.

In September 1894, Sommerfeld became Felix Klein's assistant, which included taking comprehensive notes during Klein's lectures and writing them up for the Mathematics Reading Room, as well as managing the reading room. Sommerfeld's habilitation was completed under Klein in 1895, which allowed Sommerfeld to become a Privatdozent at Göttingen. As a Privatdozent, he lectured on a wide range of mathematical and mathematical physics topics. His lectures on partial differential equations were first offered at Göttingen, and they evolved over his teaching career to become Volume VI of his textbook series Lectures on Theoretical Physics, under the title Partial Differential Equations in Physics.