Say you had a universe, like our own in every way except that the total matter in existance was one single atom. Now say you introduced another atom of roughly the same dimensions into this universe as far from the original atom as spacially possible. How long, if any time at all, would it take for either atom to "observe" the existance of the other? Meaning: Is the force of gravity an instantaneous force, or does the force travel ie... as in a gravity wave? If the atoms are say 100 million light years apart, would either be aware of the other's existance untill 100 million years after the 2nd atom was introduced, or would they somehow instantly experiance the distortion of spacetime due to each others mass? Would they be able to "feel" each other before they could "see" each other?