Well, the question "Who invented Time Travel?" implies that someone intentionally set out to discover/invent controlled time travel. That being the question, I have no answer yet. But, if I recall correctly, when an object's speed is faster than its surroundings, time slows down for that object (actually only happens for relativisitc speeds). So, since no human has approached relativistic speeds, then no one has achieved time travel by this method.
This little exercise certainly set in motion the cogs and wheels turning in my head. I would think that time is "moving" at a constant rate. I came across this ideal visually by imagining a series of particles in 2D space with trajectories. All particles are bouncing into one another (much like the "planets" screensaver some of us have seen). Now take that 2D motion in a plane and add the third dimention moving at a constant rate. You would see the plane of 2D particles moving along an axis normal to the plane with the particles moving about. As the particles move about, they plot out 3D trajectories as the plane moves in one direction. From the perspective of being outside the plane, one could tell future or past position of any particle by looking along the trajectories that have predetermined paths.
Now extending this analogy to people might explain how psychics are able to sometimes accurately predict future and past events of people they come in contact with. This assumes the psychics are not mentally ill, or fakes, or any other type of crack pot (i.e. the real true blue psychic such as John Edward who is able to predict some future events though his real gift appears to be talking to dead people). While I don't think psychics can transcend the space-time contunuum and leave the rate constant of time, I do know that the human brain is a non-linear processing system, and somehow these people are able to predict with limited accuracy future events and tell of past events which they previously knew nothing about by taking a few bits of present information and computing/extrapolating along the trajectory a little away from the constantly moving "plane" (from our perspective a cube or sorts) of space.
Of course this little mental exercise is probably bogus and full of nonsense.
