Technical definition of time is relative movement. Ticks of a second hand on a clock in relation to the sun moving across the sky. Car moving in relation to the buildings on the road it travels. If true, then how does general relativity and special relativity actually cause changes in relative movement? Seems like relativity gave up on trying to figure it out. HOW does something near a large sun or blackhole actually stop in it's tracks for billions of years? Time travel is really 'Movement travel'. This is real reason physicists don't think backwards 'movement travel' can happen. Only slowing of it so you see the world outside of the field speed up in relation to yourself. Of course physicists proved that time slows on jet airplanes in relation to the ground however nobody explains why. Since they lack the 'why' then why couldn't we go back in movement(time)? Time travel is the concept where our understanding of causality fails. Imagine if you were driving a car and suddenly it would stop for no reason or back up for no reason while you see the whole world around ya reverse their direction of movement. Would seem like magic. So again, what can possibly cause things to stop? I mean gravity causes things to move towards each other, not stop moving entirely. So again I ask why? side note: 'energy' isn't an answer.