Abstract
Different or conflicting accounts of the same episode in the history of science may arise from viewing that episode from different perspectives. The metaphor suggests that conflicting accounts can be seen as complementary, constructing a multi-dimensional understanding, if the different perspectives can be coordinated. As an example, I discuss different perspectives on the Stern-Gerlach experiment. In a static interpretation, the SGE has been viewed as an experiment that allows the determination of the magnetic moment of silver atoms. Based on the concept of magnetic momentum arising from orbital angular momentum, the original experiment was designed in 1922 as an experimentum crucis to decide between Bohr’s quantum theory and classical electromagnetic theory, and its outcome was interpreted as a confirmation of the Bohr-Sommerfeld quantum postulates. After the advent of quantum mechanics, the SGE was reinterpreted in terms of magnetic moment arising from the electron’s spin angular momentum. In a dynamical interpretation, physicists have asked for the physical mechanism responsible for the quantization of the angular momentum with respect to the direction of the magnetic field. Although different suggestions were explored, none was ever accepted as fully satisfactory. Today this difficulty is seen as a paradigmatic instance of the unsolved quantum measurement problem.
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Notes
- 1.
The historical SGE is not a good experiment for ad oculos demonstration purposes, as it is difficult to do and the results are not easily transparent for display in a classroom. But its principle can be easily visualized and conveyed in schematic and idealized displays.
- 2.
- 3.
We will keep in the following the distinction between “a” SGE and “the” SGE. This distinction does not preclude that “the” SGE was an extended process of experimentation with various distinct stages, see note 9 below.
- 4.
The replication of parts of the SGE was done by Trageser (2011) in the context of his larger reconstruction of the genesis and early development of the SGE. Certain aspects of the historical SGE were also put to a replicative test by Friedrich and Herschbach (2003). There exists a large body of literature on replication of historical experiments which cannot be reviewed here.
- 5.
The expression “idealized material constellation” may sound paradoxical. It refers to the fact that “a” SGE can be done in many ways, using different materials, vacuum technology, geometries, etc. Whether any such material constellation would be permissible to constitute an SGE depends on the idea of the SGE, which tells you, e.g., that the magnetic field has to have a gradient, etc. But any defining aspect of such an SGE must be realized in some way or other materially. The SGE is not a thought experiment.
- 6.
This continuity was established, e.g., by Otto Stern’s successful efforts in establishing a program of molecular beam experimentation in his laboratory in Hamburg, indicated, e.g., by a series of publications from his laboratory which explicitly were called “Untersuchungen zur Molekularstrahlmethode aus dem Institut für physikalische Chemie der Hamburgischen Universität” (Toennies et al. 2011). Walther Gerlach, too, for a while continued to do experiments similar to the original SGE but then changed to other fields, see Friedrich and Herschbach (2005).
- 7.
One may be reminded here of the confirmation of gravitational light bending by the British eclipse expedition of 1919. Here the theoretical alternatives were also threefold: no deflection according to Newtonian gravitation and classical wave theory or according to Nordström’s relativistic theory, deflection of \(0.85''\) according to Newtonian gravity and light corpuscles, or calculations based only on the equivalence hypothesis, and a deflection of \(1.7''\) for Einstein’s general theory of relativity. The observations decided in favor of the third alternative. In this case, not only the experimental result proved to be robust, Einstein’s theory of general relativity, too, remained valid to this day.
- 8.
I still have to find the place where the historical SGE is explicitly reinterpreted in terms of electron spin versus orbital momentum quantization. Perhaps there is a dark period here in which the SGE was not interpreted at all, and when it was interpreted again it was done so in the new framework without reference to the old Bohr theory.
- 9.
More precisely, the SGE developed with ever increasing accuracy. The first paper (Gerlach and Stern 1921) only reports a broadening of the silver deposits in the presence of a magnetic field, demonstrating the causal relevance of the field for some kind of broadening of the beam. The magnetic field affected the motion of the silver atoms, at least in some way. This first result was interpreted as demonstrating that the silver atoms do indeed carry an angular momentum. Only after further instrumental refinements was it possible to see that the silver deposits on the plate were showing the characteristic bipartite splitting, at which stage the causal inference was that the inhomogeneous magnetic field was causally relevant for a splitting of the beam (Gerlach and Stern 1922b). Still further refinements finally also made a numerical evaluation of the hypothesized magnetic moment possible (Gerlach and Stern 1922a).
- 10.
Note that this textbook was written from the point of view of the standard Copenhagen interpretation i.e., before Bohm began to question that by then canonical understanding and to investigate the alternative interpretations of quantum theory for which he is best known today.
References
Bernstein, J. 2010. The Stern-Gerlach experiment. arXiv:1007.2435.
Bohm, D. 1951. Quantum theory. Englewood Cliffs, NJ: Prentice-Hall.
Einstein, A., and P. Ehrenfest. 1922. Quantentheoretische Bemerkungen zum Experiment von Stern und Gerlach. Zeitschrift für Physik 11:31–34. Reprinted in Kormos Buchwald et al., 2012, Doc. 315d.
Friedrich, B., and D. Herschbach. 1998. Otto Stern’s lucky star. Daedalus 127(1): 165–191.
Friedrich, B., and D. Herschbach. 2003. Stern and Gerlach: How a bad cigar helped reorient atomic physics. Physics Today 56(12): 53–59.
Friedrich, B., and D. Herschbach. 2005. Stern and Gerlach at Frankfurt: Experimental proof of space quantization. In Stern-Stunden. Höhepunkte Frankfurter Physik, ed. W. Trageser. Frankfurt: University of Frankfurt, Fachbereich Physik.
Gerlach, W. 1969. Otto Stern zum Gedenken. Physikalische Blätter 25(9): 412–413.
Gerlach, W., and O. Stern. 1921. Der experimentelle Nachweis des magnetischen Moments des Silberatoms. Zeitschrift für Physik 8: 110–111.
Gerlach, W., and O. Stern. 1922a. Das magnetische Moment des Silberatoms. Zeitschrift für Physik 9: 353–355.
Gerlach, W., and O. Stern. 1922b. Der experimentelle Nachweis der Richtungsquantelung im Magnetfeld. Zeitschrift für Physik 9: 349–352.
Gerlach, W., and O. Stern. 1924. Über die Richtungsquantelung im Magnetfeld. Annalen der Physik 74: 673–699.
Kormos Buchwald, D., Illy, J., Rosenkranz, Z., and T. Sauer, T. (eds.). 2012. The Collected Papers of Albert Einstein, Vol. 13. The Berlin Years: Writings & Correspondence, January 1922–March 1923. Princeton: Princeton University Press.
Mehra, J., and Rechenberg (eds.). 1982. The historical development of quantum theory, Vol. 1 in 2 parts. The quantum theory of Planck, Einstein and Sommerfeld: Its foundation and the rise of its difficulties 1900–1925. New York, Heidelberg, Berlin: Springer Verlag.
Schmidt-Böcking, H., and K. Reich. 2011. Otto Stern. Physiker, Querdenker, Nobelpreisträger. Frankfurt/Main: Societäts-Verlag.
Schmidt-Böcking, H., and W. Trageser. 2012. Ein fast vergessener Pionier. Physik Journal 11(3): 47–51.
Schütz, W. 1969. Persönliche Erinnerungen an die Entdeckung des Stern-Gerlach-Effektes. Physikalische Blätter 25(8): 343–345.
Stern, O. 1921. Ein Weg zur experimentellen Prüfung der Richtungsquantelung. Zeitschrift für Physik 7: 249–253.
Toennies, J.P., H. Schmidt-Böcking, B. Friedrich, and J.C. Lower. 2011. Otto Stern (1888–1969): The founding father of experimental atomic physics. Annalen der Physik 523(12): 1045–1070.
Trageser, W. 2011. Der Stern-Gerlach-Effekt. Genese, Entwicklung und Rekonstruktion eines Grundexperimentes der Quantentheorie 1916–1926. Ph.D. Thesis, Johann Wolfgang Goethe-Universität Frankfurt.
Unna, I., and T. Sauer. 2013. Einstein, Ehrenfest, and the quantum measurement problem. Annalen der Physik 525(1–2): A15–A19.
Weinert, F. 1995. Wrong theory—right experiment: The significance of the Stern-Gerlach experiments. Studies in the History and Philosophy of Modern Physics 26(1):75–86.
Acknowledgments
My understanding of the SGE effect has profited a lot from discussions with Horst Schmidt-Böcking and Wolfgang Trageser. I also thank Tim Räz, Raphael Scholl, and Adrian Wüthrich for helpful criticism of an earlier version of this paper.
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Sauer, T. (2016). Multiple Perspectives on the Stern-Gerlach Experiment. In: Sauer, T., Scholl, R. (eds) The Philosophy of Historical Case Studies. Boston Studies in the Philosophy and History of Science, vol 319. Springer, Cham. https://doi.org/10.1007/978-3-319-30229-4_12
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