How does adding rotation to a freely falling particle violate the Einstein equivalence principle?

I realize there is a similar post here:

An example of a theory that respects the Weak Equivalence Principle but violates the Einstein Equivalence Principle

but I failed to understand the response after reading it a number of times.

  • $\begingroup$ Just to clear, because I have a related question, not an answer, is this the extract that is the problem for you We could imagine a theory of gravity in which freely falling particles begin to rotate as they moved through a gravitational field. Then they could fall along the same paths as they would in an accelerated frame (thereby satisfying the WEP), but you could nevertheless detect the existence of the gravitational field (in violation of the EEP). Such theories seem contrived, but there is no law of nature that forbids them. $\endgroup$
    – user108787
    Nov 4, 2016 at 17:42
  • 1
    $\begingroup$ Yes, it's from Carroll. $\endgroup$ Nov 4, 2016 at 19:14
  • $\begingroup$ Wouldn't the gravitational field have to have torsion for this to happen, if it was GR? $\endgroup$
    – Bob Bee
    Nov 5, 2016 at 6:41
  • $\begingroup$ Could you explain more please @Bob? $\endgroup$ Nov 5, 2016 at 17:54


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