  The vacuum is considered as some fluid emergent from the zero-point
fluctuations of the quantum fields contributing to the vacuum energy density
and pressure. The equation of vacuum state and the speed of vacuum sound-waves
are deduced under the assumption of zero vacuum entropy. The evolution of the
background space-time metric resembles that of the Milne's-like universe. In
the framework of the five-vector theory of gravitation allowing an arbitrary
choice of the energy density reference level, the dynamics of the vacuum,
pressureless matter, and space-time metrics perturbations are traced under this
background. The obtained results show the very early formation of the Universe
structure without the need for dark matter. Thus, a vacuum can be considered as
some of the dark-energy-matter unification.
