  The holographic principle sets an upper bound on the total entropy content of
the Universe. Within the limits of a Newtonian approximation, a
quantum-mechanical model is presented to describe the cosmological fluid. Under
the assumption that gravitational equipotential surfaces can be identified with
isoentropic surfaces, this model allows for a simple computation of the
gravitational entropy of the Universe. The results thus obtained no longer
saturate the holographic bound, thus representing a considerable improvement on
previous theoretical estimates.
