Could anyone explain:
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?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.