Otto Stern - An Involuntary Convert to Quantum Physics
Břetislav Friedrich
The bulk of experiments and observations that lined the path to quantum mechanics amounted to a backlog of data in need of explanation. A notable exception was the Stern-Gerlach experiment (SGE) designed to test the predictions of the Old Quantum Theory as embodied by the 1913-1916 Bohr-Sommerfeld-Debye atom model. After its initial triumphs, such as the explanation of the astrophysically observed spectrum of He+, this model was frowned upon in some quarters, mainly because of its ad hoc nature. Otto Stern (1888-1969) – and his close colleague and friend, Max von Laue (1879-1960) – even took a vow: “If this nonsense of Bohr should, in the end, prove to be right, we will quit physics.” Stern would go further yet and, in 1920, devise an experiment – the SGE – to disprove Bohr’s model. However, contrary to Stern’s expectations, the SGE ruled unequivocally in favor of the model and its amendments. Wolfgang Pauli (1900-1958) quipped: “That should convert even the non-believer Stern.” And it did: Confronted with the outcome of the SGE, Stern noted in 1961: “I still have objections to the idea of beauty of quantum mechanics. But she is correct.” Ironically, the SGE would epitomize quantum mechanics as we know it: whether quantum measurement, state preparation, coherence, or entanglement – apart from the quantization of angular momentum and its spatial projections – the SGE has it all. The descendants of the SGE include transformative techniques for the study of the quantum properties of nuclear, atomic, molecular, and condensed-matter systems, with Magnetic Resonance Imaging (MRI) being among the most widely used.
•Apr 1, 2026•0 citations