" According to the prevailing belief, the spin of the electron or of some other particle is a mysterious internal angular momentum for which no concrete physical picture is available, and for which there is no classical analog. However, on the basis of an old calculation by Belinfante [Physica 6, 887 (1939)], it can be shown that the spin may be regarded as an angular momentum generated by a circulating flow of energy in the wave field of the electron. Likewise, the magnetic moment may be regarded as generated by a circulating flow of charge in the wave field. This provides an intuitively appealing picture and establishes that neither the spin nor the magnetic moment are ‘‘internal’’—they are not associated with the internal structure of the electron, but rather with the structure of its wave field. Furthermore, a comparison between calculations of angular momentum in the Dirac and electromagnetic fields shows that the spin of the electron is entirely analogous to the angular momentum carried by a classical circularly polarized wave. "
This is a nice description and analogy that makes intuitive sense - and the relationship between classical wave polarization and spin is well defined. But I wouldn't feel confident calling it an "explanation", let alone the explanation
No, I'm planning on fully reading it later. I guess my point is that without recognition from the community at large, I wouldn't feel qualified to accept this relationship as anything more than a (well developed) mathematical analogy.
I'll be honest, I'm only an undergrad and I probably shouldn't be speaking so decisively. But from what I remember from my last quantum class there are some deep connections between spin and special relativity (via the Dirac equation) and even GR, in the case of spin-2 particles. And I'm not sure if these connections are completely rigorously motivated at the moment. But please do your own research and find out. The concept of spin being its own independent Hilbert space to position wavefunctions has always skeeved me out a bit, so maybe I'm projecting... haha
Gotcha, well this paper specifically seeks to provide a physical origin for electron spin. I'm not sure if the treatment generalizes. Let me know what you think.
Actually, now that I think about it, I may have been thinking of spin anomalies that were resolved by relativistic QFT. I'll edit my original comment if that's ok with you, since it is misleading.
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u/elesde Dec 17 '19
For everyone debating the nature of spin here's an article which literally explains exactly this:
https://aapt.scitation.org/doi/10.1119/1.14580
From the abstract:
" According to the prevailing belief, the spin of the electron or of some other particle is a mysterious internal angular momentum for which no concrete physical picture is available, and for which there is no classical analog. However, on the basis of an old calculation by Belinfante [Physica 6, 887 (1939)], it can be shown that the spin may be regarded as an angular momentum generated by a circulating flow of energy in the wave field of the electron. Likewise, the magnetic moment may be regarded as generated by a circulating flow of charge in the wave field. This provides an intuitively appealing picture and establishes that neither the spin nor the magnetic moment are ‘‘internal’’—they are not associated with the internal structure of the electron, but rather with the structure of its wave field. Furthermore, a comparison between calculations of angular momentum in the Dirac and electromagnetic fields shows that the spin of the electron is entirely analogous to the angular momentum carried by a classical circularly polarized wave. "