Alfred Landé

German-American physicist known for his contributions to quantum theory. He is responsible for the Landé g-factor an explanation of the Zeeman Effect.

Landé obtained his doctorate under Sommerfeld at the University of Munich, two weeks prior to the start of the First World War. He joined the Red Cross and served for two years on the eastern front before being invited by Max Born to join him at the Artillery Testing Commission, one of the few scientific sections of the army. Apart from their work on artillery location by sound ranging, they began to examine the cohesive forces and compressibility of crystals. This work led to the unexpected result that the electron trajectories in atoms were not at all like planetary orbits, which at the time was the usual understanding of the electron in an atom.

Landé studied atomic structure intensively for the next seven years. In 1916 Sommerfeld had begun to apply the new atomic theory to form a general quantization rule. Landé's work over cubic and tetrahedral electron trajectories ("cube atoms") became of great interest to Sommerfeld, Peter Debye and Bohr.

In 1919 Landé unexpectedly turned to spectroscopy even though the continuation of the study of the spatial orientation of the atoms was the most pressing problem of the time. He turned to the problem of atoms with several electrons, in particular to the simplest case, the spectrum of helium. The spectroscopy of helium had been examined experimentally by Friedrich Paschen, but there did not exist a theoretical interpretation. The spectrum showed non-combining single and double (actually triplet, as it turned out later) terms so that it seemed as if helium was made of two different substances (which is explained today as the result of electron spin).

Landé's work contained several new important ideas, including the rule of vector addition of two quantum-mechanical angular momenta J1 and J2. His findings and postulates were later confirmed by quantum theory.