  The astronomical observations indicate that the universe expands with
acceleration and it has a finite event horizon. The recent CMB observations
confirm the universe is homogeneous, isotropic and asymptotically flat. The
total gravitational energy of a body having mass m is the gravitational
potential energy originating from the gravitational interaction of the body
with all masses of the universe, within the event horizon. The flat geometry of
the universe enables to determine the total gravitational energy of the mass m
within the framework of the Newtonian gravity in Euclidean space. By this
approach, it has been found the modulus of the total gravitational energy of a
body is close to its rest energy E = m*c^2, which is a remarkable result.
Besides, the smoothed gravitational potential in an arbitrary point of the
observable universe appears close to - c^2, where c is the speed of the light.
