| 1932: Re-election of Hindenburg as
President of the Empire | Aldous Huxley: Brave New World | Discovery of
positron and neutron | Auguste Piccard: Balloon take-off into the stratosphere
| Climax of World economic crisist der Weltwirtschaftskrise |
| Deutsch |
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The Controversy about Electron Spin |
| In Holland the State University Leiden was a
prominent centre for theoretical physics. At the end of the nineteenth and the
beginning of the twentieth century, Hendrik Antoon Lorentz (1853-1929) had
worked there. His successor, on the recommendation of Albert Einstein, was the
Austrian Paul Ehrenfest, whom Wolfgang Pauli had
already met in 1922 during the "Bohr Festival" in Göttingen.
In 1925 Ehrenfest's assistants Georg Eugen Uhlenbeck (1900-1988)
and Samuel Abraham Goudsmit (1902-1978) had the idea of electron spin, i.e. a
clearly imaginable rotation of the electron on its axis. This hypothesis had
already been proposed by Ralph Kronig (1904-1995), who was later Pauli's
assistant in Zurich. |
Wolfgang Pauli and Paul Ehrenfest
© CERN, Geneva |
Many theoretical physicists, Pauli
among them, considered this idea to be inacceptable and too descriptive. On the
other hand, at this time Heisenberg's matrix mechanics were being developed,
which were anything but pictorial, in which the conception of electron orbits
in the atom was expressly avoided. With the aid of electron spin, however,
certain properties of the hydrogen spectra were able to be interpreted
satisfactorily. The main difficulty was the difference of a factor 2 between
the calculated and observed doublet splitting. So a lively oral and written
discussion broke out. Characteristically, the problem was considered to have
been resolved after Pauli was able to be convinced. In retrospect Goudsmit
wrote in 1965 that Pauli had abandoned his critical, negative position in March
1926 and had informed him of this on a postcard. Today, electron spin is
considered to be a quantum mechanical property with the dimension of angular
momentum. It can take only two values, +1/2 and -1/2, in quantum mechanical
units. Electrons are hence governed by the Pauli principle. |
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