A repulsive force in the Einstein theory

The Laser Interferometer Gravitational-Wave Observatory (LIGO) detection of gravitational waves that take away 5 per cent of the total mass of two merging black holes points out on the importance of considering varying gravitational mass of a system in the framework of the Einstein general theory of relativity. We calculate the acceleration of a particle in the non-stationary field of a quasi-spherical system composed of a large number of objects emitting gravitational waves. It is shown that reduction of the gravitational mass of the system due to emitting gravitational waves leads to a repulsive gravitational force that diminishes with time but never disappears. This repulsive force may be related to the observed expansion of the Universe.