Foundations of Physics

, Volume 39, Issue 10, pp 1177–1190

The Stern–Gerlach Phenomenon According to Classical Electrodynamics


DOI: 10.1007/s10701-009-9338-1

Cite this article as:
França, H.M. Found Phys (2009) 39: 1177. doi:10.1007/s10701-009-9338-1


We present a description of the Stern–Gerlach type experiments using only the concepts of classical electrodynamics and the Newton’s equations of motion. The quantization of the projections of the spin (or the projections of the magnetic dipole) is not introduced in our calculations. The main characteristic of our approach is a quantitative analysis of the motion of the magnetic atoms at the entrance of the magnetic field region. This study reveals a mechanism which modifies continuously the orientation of the magnetic dipole of the atom in a very short time interval, at the entrance of the magnetic field region. The mechanism is based on the conservation of the total energy associated with a magnetic dipole which moves in a non uniform magnetic field generated by an electromagnet. A detailed quantitative comparison with the (1922) Stern–Gerlach experiment and the didactical (1967) experiment by J.R. Zacharias is presented. We conclude, contrary to the original Stern–Gerlach statement, that the classical explanations are not ruled out by the experimental data.


Foundations of quantum mechanicsSpin quantizationStern–Gerlach experiment

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© Springer Science+Business Media, LLC 2009

Authors and Affiliations

  1. 1.Instituto de FísicaUniversidade de São Paulo C.P. 66318São PauloBrazil