Polykarp Kusch

It’s the birthday of Polykarp Kusch, who was born in 1911 in Blankenburg, Germany. A year after Polykarp’s birth, the Kusch family emigrated to the US. Kusch earned his physics PhD at the University of Illinois and moved to Columbia University in 1937 to work with I I Rabi and others in the new field of molecular radio frequency spectroscopy. Starting in 1945, Kusch began a series of experiments to determine the magnetic moment of the electron. From his measurements of three different atomic species, he concluded that the moment’s value differed slightly but significantly from the value derived from the Dirac equation. The discrepancy was explained in 1948 by Julian Schwinger as a manifestation of the new theory of quantum electrodynamics (QED). Kusch was awarded the 1955 Nobel physics prize for his discovery along with Willis Lamb, who had measured a different manifestation of QED, a small but significant difference between the energies of hydrogen’s 2S1/2 and 2P1/2 orbitals.

Date in History: 26 January 1911