We use measurements of the polarization of light from a magnetic white dwarf to impose sharp constraints on the gravity-induced birefringence of space predicted by a broad class of nonmetric gravitation theories. Since gravity-induced birefringence violates the Einstein equivalence principle, our measurements test this foundation of general relativity and other metric gravitation theories in a new setting.

• Received 27 May 1998

DOI:https://doi.org/10.1103/PhysRevD.59.047101