#### atyy

Science Advisor

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(1) It is a fundamental postulate consistent with the EP that is experimentally verified.

(2) It is derived from more fundamental postulates such as the Hilbert action with minimally coupled matter as an approximation for very small extended bodies.

Can Fermi-Walker transport of a gyroscope along a worldline be seen in the same 2 ways, as either a fundamental postulate consistent with the EP, or derived as the small body approximation for a rotating extended body? In the second case, googling seems to indicate that the equations for the extended body are the Mathisson-Papapetrou equations. Is that right, or are there other derivations?