Theoretically you can travel back in time by moving faster than the speed of light, or the universal speed limit. Is there a minimum speed? 0. But with gravity you would be moving, so if you move against gravity relative to yourself you are moving. So if there was a place in the universe free of a gravitational pull or the gravitational pull was the same from all sides you would be moving at a true 0. So my question is; can you stop moving and if so is that the minimum speed, and if it is what would time do? would it take you to the future?