The Friedmann Paradigm: A critical review

The Friedmann paradigm for a dynamical universe emanating from a spacetime singularity is critically reviwed. Quantum effects, playing the essential role at the very early stages, suggests that the universe may follow different course to that presented by the standard Friedmann solutions. The investigation of the back-reaction effect of the vacuum energy of quantized massless matter fields at finite temperatures shows that the original spatial singularity is avoided and that the universe is maintained all times at a critical density. Instead of having a universe that was created at once we have an emergent universe with energy being created continuously so as to maintain the overall density at its critical value. The calculations presented here provide a basis to construct a dynamical model for the universe where all the known problems of the standard big bang can be avioded from start without the need to assume the occurence of an inflation phase.