Geometrical optics in the rotating Einstein universe

The geodesic equation for rays of light is solved for the Ozsvath class I cosmological model. The terms of first order in a parameter which describes the deviation from the static Einstein universe are used for calculating the caustics. Quaternion techniques for performing the calculations are developed. Particular attention is paid to the formation of edges on the caustics. The way the edges prevent causality violating closed null-like curves is demonstrated. The observed transversal motion of galaxies is calculated. Ways of determining the causality observationally are discussed. (Author)