An expanding universe is a solution to Einstein's equations. So particles become farther apart with time. I wonder how the conservation of energy is accounted for in this expansion. Does the gravitational potential energy increase as the expansion of space creates greater distance between objects (galaxies)? Does the velocity created by increasing distance also contribute to the kenitic energy of galaxies? It seems that expanding space would contribute to both potential and kenitic energy when normally you'd expect a decrease of kenitic energy with an increase of potential energy. I doubt that the expansion of space contributes to the kenetic energy of receeding galaxies. For I am told that the expansion can be faster than light. And that would cause the relativistic mass to increase to infinity if the expansion contributed to the velocity of galaxies. So if the expansion of space does not contribute to the momentum or kenetic energy of galaxies, but it does contribute to the gravitational potential energy, then the conservation of energy is violated unless mass decreases with expansion. Right?