  The physical nature of the presently dominating enigmatic dark energy in the
expanding universe is demonstrated to be explainable as an excess of the
kinetic energy with respect to its potential energy. According to traditional
Friedman cosmology, any non-zero value of the total energy integral is ascribed
to the space curvature. However, as we show, in the flat universe the total
energy also can be different from zero. Initially, a very small excess of
kinetic energy originates from the early universe. The present observational
data show that our universe has probably a flat space with an excess of kinetic
energy. The evolutionary scenario shows that the universe presently is in the
transitional stage where its radial coordinate expansion approaches the
velocity of light. A possibility of the closed Bubble universe with the local
Big Bang and everlasting expansion is demonstrated. Dark matter can be
essentially contributed by the non-relativistic massive neutrinos, which have
cooled to very low temperatures and velocities thus favoring the formation of
the observed broad equipotential wells in galaxies.
