Deflection of polarised radiation: relative phase delay technique

The weak equivalence principle states that the world line of a freely falling test particle is independent of its structure and composition. Until recently experiments designed to detect variations in the geodesic motion of test particles of differing internal properties have been confined to particles of non-zero rest mass. The experiment discussed here applies the same question to photons by asking whether oppositely polarised photons fall at the same rate. (author)