It's a measurement of movement, but it is all relative, since our position as observer influences our measuring. There's no time travelling to do, because there's no 'place' we can go to observe the same relational effects. The time travel genre just pretends past and future are places we could move back or forward to. But there's no way to put your hand in a river, and then some how pull back all those molecules, maintaining the same relationship between your hand and the relation all those molecules had with each other.