GRAVITATIONAL ENERGY IN THE EXPANDING UNIVERSE

The role of gravitational energy in the evolution of the universe is examined. In co-moving coordinates, calculation of the Landau-Lifshitz, pseudotensor for FRW models reveals that: (i) the total energy of a spatially closed universe irrespective of the equation of state of the cosmic fluid is zero at all times, (ii) the total energy enclosed within any finite volume of the spatially flat universe is zero at all times, (iii) during inflation the vacuum energy driving the accelerated expansion and ultimately responsible for the creation of matter (radiation) in the universe, is drawn from the energy of the gravitational field. In a similar fashion, certain cosmological models which abandon adiabaticity by allowing for particle creation, use the gravitational energy directly as an energy source.