A new test of the equivalence principle: a null phase-delay experiment

The Einstein Equivalence Principle (EEP) provides the fundamental basis for any metric theory of gravity, such as general relativity. It implies that the only observable effects of gravitation are those mediated by the spacetime metric. Therefore, at the origin of a local freely falling frame there should be no observable effects of gravity. Null redshift tests provide an interesting way to test this prediction. In this test, the frequencies of two oscillators of a different type are compared at the same location in a gravitational field as the field is varied. Any variation in the frequency would signal a violation of the EEP. Here we shall propose a new test of the EEP called a null phase-delay experiment, in which the phase-delay of a signal propagated over a coil of optical fiber is monitored as the gravitational field at the coil is varied. An interesting test of the EEP in the solar gravitational field can be performed in the laboratory under carefully controlled conditions. With presently available technology, such an experiment could provide a 0.01% test.This essay received the third award from the Gravity Research Foundation, 1993-Ed.