From previous answers - according to the general theory of relativity, kinetic energy contributes to gravitational mass. A body in motion posseses kinetic energy plus mass. Energy and mass are equivalent under GR. Particle colliders routinely confirm this prediction. Crash two particles together at relativistic velocities and you create particles with more mass than the sum of the two crashed particles. If we look at the motion of the objects in the universe, would this not explain the missing 'dark matter'? If not, perhaps it means the whole universe is moving quite fast...(we would never know) ?