Symmetry

Special Issue: Advances in Spin Physics

Sergey Mikhailovich Troshin

Published Jun 30, 2022• 0 citations

Abstract

The notion of spin entered physics about one hundred years ago when Uhlenbeck and Goudsmit introduced the internal degree of freedom for the electron- spin as a real physical characteristics instead of the so called non-mechanical strength used at first by Pauli under formulation of his famous principle [...]

DOI: 10.3390/sym14071355

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Spin (1925)

S. Brandt

Abstract We have seen in the preceding episode that early in 1925 Pauli attributed to the electron a ‘classically not describable two-valuedness’. Within a few months this property of the electron was given a physical description which, it is true, is not satisfactory from the viewpoint of classical physics. This description is regarded as the discovery of the intrinsic angular momentum or spin of the electron. In fact the description was given twice. Already in January Kronig discussed it with Pauli who was completely opposed to the idea so that Kronig did not publish it. The concept of the electron spin was independently proposed and published [1] by Uhlenbeck and Goudsmit who thus became the discoverers of spin.

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Goudsmit, Samuel A. It was a little over fifty years ago that George Uhlenbeck and I introduced the concept of spin. . . It is therefore not surprising that most young physicists do not know that spin had to be introduced. They think that it was revealed in Genesis or perhaps postulated by Sir Isaac Newton, which most young physicists consider to be about simultaneous.

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This article is dedicated to the 100th anniversary of quantum mechanics, and in particular to electron spin Ð a phenomenon that has no counterpart in classical physics.The hypothesis of electron spin was proposed by Uhlenbeck and Goudsmit in 1925±1926 to explain numerous experimental data.Two years later, Dirac discovered the existence of electron spin when constructing the relativistic wave equation for a free particle.This came as a great surprise to Dirac, since, as he later claimed (in 1977), his goal was to obtain a relativistic wave equation for the simplest particle, which he considered to be a particle with zero spin.But it turned out that the simplest particle is one with spin 1a2.

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Spin Wave Functions

Floyd L. Williams

In the introductory remarks to Chapter 5 mention was made of the 1925 proposal of Uhlenbeck and Goudsmit that to an electron there should be assigned an intrinsic angular momentum or spin S = (S x , S y , S z )—this in addition to its quantum angular momentum (or orbital angular momentum) M = (M x , M y , M z ) defined in (5.4.4). This is not to be taken to mean that an electron actually spins about an axis in some physical way. Experiments (in particular the noted Stern-Gerlach experiment) have provided adequate justification for the proposed concept of spin, a proposal also made by R. Bichowsky and H. Urey. Dirac has shown that the notion of spin is necessary if quantum mechanics and Einstein relativity are to be consistent theories. Chemical properties of atoms, and their ability to combine and form molecules, the splitting of spectral lines by a magnetic field applied to an atom (i.e., the Zeeman effect, which we discuss later), all depend on this important notion.

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Landmarks in the History of the Discovery of Spin in Fundamental Particles

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Abstract This chapter gets into the heart of the discovery of spin in physics as physicists try to make sense of the atomic spectra with the discovery of the anomalous Zeeman effect by Thomas Preston before the dawn of the twentieth century as Nature gave the first signal of the existence of quantum spin. Following Bohr, Sommerfeld, and Lande’s contributions with integers and then half-integers, quantum numbers make appearances, and after Uhlenbeck and Goudsmit’s ground-breaking contributions, physicists finally embrace the idea that electron spins. Pauli’s introduction of quantum spin with Pauli matrices provided a non-relativistic theory of the quantum spin. Hestenes argues that spin is not intrinsically related to Pauli matrices, and contrary to conventional wisdom, he advocates the view that the spin is very much present in the non-relativistic quantum physics.

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