  Einstein's theory predicts that, massive test particles with non-zero spin or
angular momentum, in an external gravitation field, follow geodesics which
depend upon the orientation of the spin-angular momentum . It has been claimed
that such an effect also holds for photons i.e. photons with different
helicities follow different geodesics in the gravitational field of a rotating
body and would give rise to a polarisation dependent deflection of light
passing in the vicinity of the sun or a polarisation dependent time delay of
pulsar signals . We show here that contrary to earlier claims , in Einstein's
gravity there is no birefringence and photons follow null geodesics
irrespective of polarisation. Thus if gravitational birefringence is ever
observed experimentally it would be a signal of new physics beyond Einstein's
gravity
