IS THERE EVIDENCE FOR COSMIC ANISOTROPY IN THE POLARIZATION OF DISTANT RADIO-SOURCES

Measurements of the polarization angle and orientation of cosmological radio sources may be used to search for unusual effects in the propag ation of light through the Universe. Recently, Nodland and Ralston [Ph ys. Rev. Lett. 78, 3043 (1997)] have claimed to find evidence for a re dshift-and direction-dependent rotation effect in existing data. We re examine these data and argue that there is no statistically significan t signal present. We are able to place stringent limits on hypothetica l chiral interactions of photons propagating through spacetime.