Astrophysical Searches for Lorentz Violation

Observations of photons from cosmologically distant objects yield some of the most stringent constraints on deviations from perfect Lorentz symmetry in nature. General violations of Lorentz invariance are described by the Standard-Model Extension, which predicts birefringence of light in vacuo. This talk will discuss results of recent searches for birefringence in light that has propagated over cosmological distances.