Chapter 14
Additional Topics in Quan-
tum Physics
14.1 The Stern-Gerlach experiment
In 1921, Otto Stern proposed an experiment about angular momen-
tum, shown in figure a on p. 958, that his boss at the University of
Frankfurt and many of his colleagues were certain wouldn’t work.
At this time, quantization of angular momentum had been proposed
by Niels Bohr, but most physicists, if they had heard of it at all,
thought of the idea as a philosophical metaphor or a mathemati-
cal trick that just happened to give correct results. World War I
was over, hyperinflation was getting under way in Germany (a pa-
per mark was worth a few percent of its prewar value), and the
Nazi coup was still in the future, so that Stern, a Jew, had not yet
been forced to flee to America. Because of the difficult economic
situation, Stern and his colleague Walther Gerlach scraped up some
of the funds to carry out the experiment from US banker Henry
Goldman, cofounder of the investment house Goldman-Sachs.