Equivalence Principle Tests

Nora Mills Boyd

Abstract: The Equivalence Principle supposedly plays a central role in characterizing the theory of general relativity and in particular, the geometric interpretation of gravity.  Moreover, null results from decades of experimental research looking for violations of the EP contribute support to the claim that GR has passed all experimental tests so far.  However, there is significant disconnect between formulations of the principle in theoretical physics and philosophical literatures on one hand, and experimental practice on the other.  Precise formulations of the principle typically apply strictly to abstract or highly idealized systems involving force-free ‘test’ bodies, perfectly homogeneous gravitational fields, and infinitesimally small regions. In striking contrast, EP experimentalists measure and manage forces, account for tidal effects, and capitalize on (or compensate for) the inhomogeneous gravitational environments of real, physically extended, laboratories.  So what do null results from experiments searching for EP violations actually tell us about GR?  The present project aims to bridge the gap between the conceptual foundations of GR and the experiments that supposedly support that theory.  To do this, I emphasize the importance of measuring and engineering particular gravitational environments in EP experiments.

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