  The evolution of a flat, isotropic and homogeneous universe is studied. The
background geometry in the early phases of the universe is conjectured to be
filled with causal bulk viscous cosmological fluid and dark energy. The energy
density relations obtained from the assumption of covariant conservation of
energy-momentum tensor of the background matter in the early universe are used
to derive the basic equation for the Hubble parameter $H$. The viscous
properties described by ultra-relativistic equations of state and bulk
viscosity taken from recent heavy-ion collisions and lattice QCD calculations
have been utilized to give an approximate solution of the field equations. The
cosmological constant is conjectured to be related to the energy density of the
vacuum. In this treatment, there is a clear evidence for singularity at
vanishing cosmic time $t$ indicating the dominant contribution from the dark
energy. The time evolution of $H$ seems to last for much longer time than the
ideal case, where both cosmological constant and viscosity coefficient are
entirely vanishing.
