Why cannot we say that spin of "fundamental" particles is exactly an evidence or "proof" of space-time torsion?

Remark: spin is generally a source of torsion when gravity couples to fermions, so...Why can not be said spin is torsion in disguise?


marked as duplicate by Emilio Pisanty, knzhou, Jon Custer, sammy gerbil, Kyle Kanos Feb 15 '18 at 10:56

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    $\begingroup$ Because it's not. $\endgroup$ – Slereah Feb 13 '18 at 20:39
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    $\begingroup$ Do you have a proposed mechanism for why these two should be related? As it stands I can't think of any reason this should be the case. Please go into more detail with your reasoning if you want a good answer. Also, possibly relevant answer $\endgroup$ – gabe Feb 13 '18 at 20:42
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    $\begingroup$ Possible duplicate of Spacetime Torsion, the Spin tensor, and intrinsic spin in Einstein-Cartan theory $\endgroup$ – gabe Feb 13 '18 at 20:45
  • $\begingroup$ there is some disconnected/ unconventional research into this area linking QM to fluid dynamics, solitons, and pilot wave hydrodynamics theories, reminds me of electron cycles Zitterbewegung en.wikipedia.org/wiki/Zitterbewegung try dropping by Physics Chat sometime for more investigation $\endgroup$ – vzn Feb 13 '18 at 21:10
  • $\begingroup$ There is no particular reason for spin to be a source of torsion. Dirac spinors can be coupled to ordinary torsion-free GR with no problem. Some people like Einstein-Cartan for aesthetic reasons, but it is not logically required for spinning particles. $\endgroup$ – mike stone Feb 13 '18 at 21:38