Reexamining the Classical Stern-Gerlach Effect with Simulations

Predictions of the Stern-Gerlach effect with classical magnetic moments have been commonly in error due to overlooking the constraints Maxwell's equations on a non-uniform magnetic field [1]. In addition, the role of classical spin precession in such an experiment has been debated [2,3]. We perform simulations of the Stern-Gerlach effect for ensembles of randomly oriented classical magnetic moments passing through a region of inhomogeneous magnetic field. We also explore the Stern-Gerlach deflections for polarized classical spins. Our results provide clarity to the dialogue in Refs [2,3]. A classical simulation of the Stern-Gerlach effect produced a “donut” shape after the particles passed through the non-uniform magnetic field. It results in a hole in the middle of the particle distribution, with the surrounding annulus growing in density as we move towards the outer edge of the shape.



[1] R. P. Feynman, R. B. Leighton, and M. Sands, The Feynman Lectures on Physics (Addison-Wesley, New York, 1964), Vol II, p. 35-3.

[2] P. Alstrom, P. Hjorth, and R. Mattuck, Am. J. Phys. 50, 697 (1982)

[3] S. Singh and N. K. Sharma, Am. J. Phys. 52, 274 (1984)