LIMITS ON ANISOTROPY AND INHOMOGENEITY FROM THE COSMIC BACKGROUND-RADIATION

We consider directly the equations by which matter imposes anisotropies on freely propagating background radiation, leading to a new way of using anisotropy measurements to limit the deviations of the Universe from a Friedmann-Robertson-Walker (FRW) geometry. This approach is complementary to the usual Sachs-Wolfe approach: the limits obtained are not as detailed, but they are more model independent. We also give new results about combined matter-radiation perturbations in an almost-FRW universe, and a new exact solution of the linearized equations. © 1995 The American Physical Society.