  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.
