ON SINGULARITY-FREE COSMOLOGICAL MODELS

In 1990 Senovilla(1) obtained an interesting cosmological solution of Einstein's equations that was free of the big-bang singularity, It rep resented an inhomogeneous and anisotropic cylindrical model filled wit h disordered radiation, rho = 3 rho. The model was valid,for t --> - i nfinity to t --> infinity having all physical and geometrical invarian ts finite and regular for the whole of spacetime. This was the first i nstance of a singularity-free cosmological model, satisfying all the e nergy and causality conditions and remaining true to general relativit y (On). Subsequently a family of singularity-free models has been iden tified(2). In this communication we wish to point out that a simple an d natural inhomogenization and anisotropization, appropriate for cylin drical symmetry, of the Friedman-Robertson-Walker (FRW) model with neg ative curvature leads to the same singularity-free family. It consists of the complete set of singularity-free general solutions of Einstein 's equations for perfect fluid when cylindrically symmetric metric pot entials are assumed to be separable functions of radial and time coord inates.