Abstract

In an expanding space, propagating light waves/particles participate in the expansion as originally proposed by W. H. McCrea (1962) and S. J. Prokhovnik (1963). The resulting mode of light propagation is expressed by a light "kinematic equation", which is a direct consequence of the cosmological principle and can be mathematically deduced from the Robertson-Walker metric. This leads to an important consequence, that the Minkowski light cone is transformed, in expanding space, to a curved space-time surface. Our new approach offers a more physically intelligible interpretation of the observational astronomy and theoretical cosmology and provides simple and direct answers to many abstract expositions of the conventional theory.