Limits on gravity-induced depolarization of light from the white dwarf Grw+70°8247

Abstract
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.