A PHYSICAL INTERPRETATION OF KALUZA-KLEIN COSMOLOGY

A new interpretation of five-dimensional Kaluza-Klein gravity is suggested, wherein the density and pressure of the usual four-dimensional energy-momentum tensor (T(ij)) are regarded as the extra parts of the five-dimensional Einstein tensor (G(ij)). It is shown that the physics contained in perfect-fluid. spatially flat cosmological solutions of G(ij) = T(ij) (four-dimensional) is contained in the equations G(ij) = 0 (five-dimensional). This holds irrespective of the nature of the fifth coordinate (which, however, may be related to mass). We also consider observational properties of Kaluza-Klein cosmology, notably the sizes of horizons, which we find to be smaller than in the usual theory. If this approach to cosmology is valid, the matter in the universe is a consequence of the fifth dimension, and we urge further study of this way of looking at things.