Masses and spins in curved space-time

The Poincaré and de Sitter groups are well known to imply a deep connection between the structure of space-time and particle properties (mass and spin) for cosmological models with constant four-dimensional curvature. An analogous relationship is constructed for any isotropic spatially homogeneous cosmological model. The spin is proved to be constant; a time variation of the masses of all physical systems may well exist. It is shown that the variation mt⁻¹, which arises in the context of the Friedmann model, is not precluded by present observational and experimental evidence.