The historic Stern-Gerlach experiment (SGE), which was performed in 1922 in Frankfurt, is reviewed from an experimental point of view. It is shown that the SGE apparatus is a purely classical momentum spectrometer, in which the trajectories of particles are measured. With modern detection devices the passage of each single atom can be identified and its trajectory in the magnetic field precisely determined. At the time of their experiment Stern and Gerlach achieved a hitherto unprecedented momentum resolution corresponding to an energy resolution of one μeV.
Abstract Dear Chairmen Profs. Herschbach and Toennies, dear organizers Profs. Schmidt-Böcking and Friedrich, dear Colleagues, dear Ladies and Gentlemen. The occasion for our gathering today in this location is a truly historic one: the centenary of the first quantitative experiment with molecular beams, a technique that would enable, in 1922, the first convincing proof of quantum mechanics—the fundamental theory of light and matter—and to give due honor to the pioneer physicist who developed this technique: Otto Stern.