That’s not really time travel, at least not in the sense that we commonly understand it from science fiction.
Different reference frames, accelerated to high velocity relative to each other, will experience time at different rates. But, there doesn’t yet seem to be a theory or way to go back and forth on a particular timeline.
Correct. The phenomenon I described only applies to moving ahead in time. To achieve it requires the addition of a LOT of energy. A high level of energy is required in order to sufficiently change ones state of motion, actually their velocity. Velocity is a two component vector consisting of magnitude and direction. Change one or the other, or both, sufficiently and you will noticeably move ahead in time, as compared to your stationary surroundings. The law of inertia states that objects with mass will continue moving along in a straight line at a constant rate of speed unless acted upon by an outside force. Energy = Force x Distance