If you understood the cause of Gravity, then you would know that time travel is possible as I do. Jump off a building or out of an aeroplane and you don't need fuel to accelerate. Simply creating a G-field in front of a craft would cause the craft to 'fall' towards that field which would in turn be projected further ahead causing an exponential acceleration curve up to and far exceeding the speed of light.
One must also realize that only one half of any trip could be accelerated towards and the remainder must be decelerated in the opposite direction to arrive at the destinations relative speed.