Otto Stern | Biography

Otto Stern was born in Sohrau, Upper Silesia, Germany (later Zory, Poland), on February 17, 1888. When he was four years old, his family moved to Breslau (later Wroclaw, Poland), where he attended the local Johannes Gymnasium. Most of Stern's training in science came from his home, where books, conversation and even some simple experimentation were the primary means of instruction.

As was common at the time, Stern traveled to a number of universities for his further education after graduating from the gymnasium in 1906. Finally, he undertook a doctoral program in chemistry at Breslau. He was awarded his Ph.D. in 1912 for a thesis on the kinetic theory of osmotic pressure in concentrated solutions. Through his professor's influence, Stern was able to take a position as research assistant to Albert Einstein from 1912 to 1914, first in Prague and later in Zürich, at the Federal Institute of Technology.

With the outbreak of World War I in 1914, Stern was drafted into the German army. He was assigned with the Meteorology Corps on the Russian front. During his four years in the military, Stern had enough spare time to continue his theoretical research, writing two important papers on the application of quantum theory to statistical thermodynamics during the war years.

As the war drew to a close, Stern was able to accept an appointment at the University of Frankfurt-on-the-Main. At Frankfurt, Stern became assistant to Max Born. The research topic in which Stern became interested was the use of molecular beams to study atomic and molecular properties. Stern had first learned about molecular beams during the war. The techniques for using such beams had been developed in 1911 by the French physicist Louis Dunoyer. By introducing a gas or vapor into a vacuum, a beam of atoms or molecules is formed. This beam allows the researcher to study atomic structure and properties.

Stern spent the greatest part of his professional career developing the molecular beam technology and using it to determine a number of atomic and molecular properties. The first application he studied was the determination of molecular velocities in gases. In the 1850s, James Clerk Maxwell had calculated the theoretical distribution of molecular velocities in a gas. Although there was not much doubt about the accuracy of Maxwell's findings, no empirical data supporting his results had ever been obtained. In 1920, Stern completed an experiment using the molecular beam technique to find the actual distribution of molecular velocities in a gas. His results unequivocally substantiated Maxwell's predictions.

The following year, Stern went on to a more significant application of the molecular beam technique. According to quantum theory, the atom is an electrically charged particle rotating in space. As such, it was thought to have associated with it a magnetic field whose magnetic field could be expressed as its "magnetic moment." Furthermore, the atom's magnetic moment could have only a finite, discrete number of values. This notion was described as the atom's "spatial quantization." (In fact, the same argument applies to the components of an atom, its electrons, nucleus, protons, and neutrons, all of which have their own unique magnetic moments.)

In 1922, Stern used molecular beam s to test the theory of spatial quantization. He passed a beam of silver atoms through a nonuniform magnetic field and found that it split into two distinct parts. The now famous experiment was given the name the Stern-Gerlach experiment for Stern and his associate in the work, Walther Gerlach. The experiment not only confirmed the concept of space quantization, but also allowed Stern to calculate the magnetic moment of the silver atom. His result was in agreement with the theoretical values calculated by means of quantum theory. For this experiment, and others like it carried out later, Stern was awarded the 1943 Nobel Prize in physics.

Stern's tenure at Frankfurt had ended in 1921 in the midst of planning for his famous experiment with Gerlach. The experiment was carried out at the University of Rostock, where he had been appointed associate professor of theoretical physics in 1921. Two years later, Stern moved on to the University of Hamburg. At Hamburg, Stern continued to explore the use of molecular and atomic beams. He found experimental proof for Louis Broglie' s theory of the wave nature of particles and determined the magnetic moment of the proton and deuteron, subatomic particles. The value he found for the proton was at least twice that predicted by theory, a discrepancy that has yet to be totally explained.

Adolf Hitler's rise to power in Germany convinced Stern that he had to leave his homeland. Although he was probably not in any personal danger, he resigned his post at Hamburg in protest of the new government's anti-Semitic policies. He continued his work at the Carnegie Institute in Pittsburgh and became a naturalized U.S. citizen on March 8, 1939. During World War II Stern served as a consultant to the War Department and then, in 1946, resigned his post at Carnegie to move to Berkeley. He died in a Berkeley movie theater on August 17, 1969.