Article ID: CBB000701045

Spin: All Is Not What It Seems (2007)


Spin is typically thought to be a fundamental property of the electron and other elementary particles. Although it is defined as an internal angular momentum much of our understanding of it is bound up with the mathematics of group theory. This paper traces the development of the concept of spin paying particular attention to the way that quantum mechanics has influenced its interpretation in both theoretical and experimental contexts. The received view is that electron spin was discovered experimentally by Stern and Gerlach in 1921, 5 years prior to its theoretical formulation by Goudsmit and Uhlenbeck. However, neither Goudsmit nor Uhlenbeck, nor any others involved in the debate about spin cited the Stern--Gerlach experiment as corroborating evidence. In fact, Bohr and Pauli were emphatic that the spin of a single electron could not be measured in classical experiments. In recent years experiments designed to refute the Bohr--Pauli thesis and measure electron spin have been carried out. However, a number of ambiguities surround these results---ambiguities that relate not only to the measurements themselves but to the interpretation of the experiments. After discussing these various issues I raise some philosophical questions about the ontological and epistemic status of spin. Because it is a curious hybrid of the mathematical and the physical these questions are relatively complex, and while I do not pretend to have answered them here, the goal of the paper is to uncover and isolate how spin presents problems for traditional realism and to illustrate the power that theories like quantum mechanics have for shaping both philosophical questions and answers.


Description On the development of the concept of spin in elementary particles in both theoretical and experimental contexts. Looks at the work of Otto Stern, Walther Gerlach, Samuel Goudsmit, George Uhlenbeck, Niels Bohr, and Wolfgang Pauli.

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Authors & Contributors
Greco, Pietro
Blum, Alexander
Weinert, Friedel
Stuewer, Roger H.
Shimek, Suzanne Elizabeth
Sauer, Tilman
Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics
Physics in Perspective
European Physical Journal H
European Journal of Physics
Archives Internationales d'Histoire des Sciences
Meulenhoff Boekerij B.V.
Pavia University Press
University of California, Los Angeles
Carocci Editore
Quantum mechanics
Theoretical physics
Atomic, nuclear, and particle physics
Philosophy of science
Electron physics; ionization
Bohr, Niels Henrik David
Heisenberg, Werner
Pauli, Wolfgang Ernst
Goudsmit, Samuel Abraham
Schrödinger, Erwin
Einstein, Albert
Time Periods
20th century
20th century, early
21st century
20th century, late
Bologna. Università
Massachusetts Institute of Technology, MIT

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