FIFTY YEARS OF SPIN: Personal reminiscences

JUN 01, 1976

How one student who was undecided whether to pursue a career in physics or history and another who had not taken his mechanics exam came to identify the fourth atomic quantum number with a rotation of the electron.

DOI: 10.1063/1.3023519

George E. Uhlenbeck

In a one‐page Letter to the Editor of Naturwissenschaften dated 17 October 1925, Samuel A. Goudsmit and I proposed the idea that each electron rotates with an angular momentum $ℏ/2$ and carries, besides its charge e, a magnetic moment equal to one Bohr magneton, $eℏ/2mc.$ (Here, as usual, ℏ is the modified Planck constant, m the mass of the electron and c the speed of light.) Sam, in his accompanying article, tells something of those times, fifty years ago. We have often talked about the circumstances that led to our idea, but it was mainly Goudsmit’s recollections that have appeared in print before now—they are, however, not readily accessible in English. Although I gave a short account of the discovery of the spin as a part of my inaugural address for the Lorentz professorship in Leiden in 1955, it therefore appears to be my turn to reminisce.

References

1. S. A. Goudsmit, “The discovery of the electron spin,” lecture given on the acceptance of the Max‐Planck medal, in Proceedings of the Physikertagung, Frankfurt (1965);
a German translation appeared in Physikalische Blätter, Heft 9/10 (1965).
2. S. A. Goudsmit, talk given at the 50th anniversary of the Dutch Physical Society in April 1971, Ned. Tydschrift voor Natuurkunde 37, 386 (1971); in Dutch.
3. S. A. Goudsmit, Delta 15, 77 (1972); excerpts from reference 2, in English.
4. G. Uhlenbeck, Oude en Nieuwe Vragen der Natuurkunde, North‐Holland, Amsterdam (1955);
partial English translation by B. L. van der Waerden, in Theoretical Physics in the Twentieth Century, Interscience, New York (1960).
5. E. H. Kennard, Phys. Rev. (2nd series) 19, 420 (1922).https://doi.org/PHRVAO
6. R. Kronig, “The Turning Point,” in Theoretical Physics in the Twentieth Century, Interscience, New York (1960).
7. B. L. van der Waerden, “Exclusion Principle and Spin,” in Theoretical Physics in the Twentieth Century, Interscience, New York (1960).
8. G. E. Uhlenbeck, “Reminiscences of Professor Paul Ehrenfest,” Amer. J. Phys. 24, 431 (1956).https://doi.org/AJPIAS
9. G. E. Uhlenbeck, “Over Johannes Heckius,” Comm. of the Dutch Historical Institute in Rome 4, 217 (1924).
10. Collected Papers of P. Ehrenfest, North‐Holland, Amsterdam, page 526 (1959).
11. S. A. Goudsmit, G. E. Uhlenbeck, Physica 5, 266 (1925).
12. M. Abraham, Ann. der Physik 10, 105 (1903).
13. H. A. Lorentz, Collected Works, Martinus Nyhoff, The Hague (1934), volume 7, page 179.
14. G. E. Uhlenbeck, S. A. Goudsmit, Nature 117, 264 (1926).https://doi.org/NATUAS
15. L. H. Thomas, Nature 117, 514 (1926).https://doi.org/NATUAS
16. W. Pauli, Collected Scientific Papers, volume 2, page 1080.
17. S. A. Goudsmit, PHYSICS TODAY, June 1961, page 18.
18. W. Pauli, Z. Physik 43, 601 (1927).https://doi.org/ZEPYAA
19. P. A. M. Dirac, Proc. Roy. Soc. A 117, 610 (1928);
A P. A. M. Dirac, 118, 351 (1928);
one should also not forget the contributions of H. A. Kramers: Quantentheorie des Elektrons und der Strahlung, in Hand‐ und Jahrbuch der Chemischen Physik, Akad. Verlagsges., Leipzig (1937);
English translation, Quantum Mechanics, by D. ter Haar, North‐Holland, Amsterdam (1957).

More about the Authors

George E. Uhlenbeck. Rockefeller University, New York.