Einstein or Einstein–Cartan?

  • Thread starter Dmitry67
  • Start date
Could anyone explain:

1 As the master theory of classical physics general relativity has one known flaw: it cannot describe "spin-orbit coupling", i.e., exchange of intrinsic angular momentum (spin) and orbital angular momentum.

2 There is a qualitative proof showing that general relativity must be extended to Einstein-Cartan theory when matter with spin is present.

3 Experimental effects are too small to be observed at the present time because the spin tensor of typical macroscopic objects is often small and torsion is nonpropagating which means that torsion will only appear within a massive body. In addition, only spinning objects couple to torsion.
I dont understand why if #3 (Experimental effects are too small to be observed) there is a 'proof' #2? What is a 'flaw' if there are no observed effects?


Gold Member
I think #2 and #3 are independent of each other. In order to accomodate spin-orbit coupling a theory must have an asymmetric affine connection. This is not true of GR but is the case for Einstein-Cartan theory. That is a fact and does not depend on the fact that the effects of SO coupling are very small in weak field and small spin regimes.

I think the article is saying that with our present data, it isn't possible to separate the two theories.

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