Null geodesics, caustics and apparent motion of galaxies in a finite rotating universe

Null solutions of the geodesic equation are presented for a universe which can be regarded as a rotating and shearing generalization of the static Einstein universe (the Ozsvath class I model). It is shown how the closest caustic, which in the static case just consists of one point at the antipode, grows to form two interwoven closed surfaces when motion is introduced It is further shown how they prevent causality violating null-like curves. The observed transversal motion of matter (the global rotation) is calculated. The conclusions concerning the causality of the universe which an observer might draw from the global rotation are discussed. (author)