Hertz, Gustav (1887–1975)

German physicist who, with US physicist James Franck, demonstrated that mercury atoms, when bombarded with electrons, absorb energy in discrete units (or quanta). Following the absorption of energy, the atoms return to their original state by emitting a photon of light. This was the first experimental proof that the quantum theory of atoms was correct and demonstrated the reality of atomic energy levels. He shared the Nobel Prize for Physics in 1925, with Franck, for the discovery of the laws governing the impact of an electron upon an atom.

Gustav Hertz was born in Hamburg, Germany, and obtained his doctorate in Berlin in 1911. He became an assistant in the Berlin physics institute and began his collaboration with Franck. He was professor of experimental physics at the University of Halle 1925–1927. From 1928 to 1935 he worked at the Berlin Techniche Hochschule. Because of his Jewish descent, Hertz was forced to resign in 1935. However, he remained in Germany during World War II, working as director of the Siemens Research laboratory, Berlin. After the war, he was captured by the Russians and taken to the USSR to continue his work in atomic physics. In 1955 he re-emerged as director of the Physics Institute in Leipzig, East Germany. He is the nephew of Heinrich Hertz, the discoverer of radio waves.