The problem with time travel is that even if it was possible to revisit past events, i.e. move back again along the 4th dimension, it would be impossible to change anything because all of the atoms, electrical charges and other sub-atomic particles which have moved, interacted, reacted and so on would be back in their original positions with their original momentums and charges, once the play button was pressed on the 4th dimension once again, all of the atoms, charges and sub-atomic particles would resume their merry dance and end up exactly where they were at the moment you travelled back in time, in effect, going back in time wouldn't change anything because you can't bend the 4th dimension like a train track, you can only imagine replaying a past event.. although it would happen exactly the same as before..

It would like trying to bend up so it becomes down...impossible, up is up. (Up being an absolute direction not a direction relative to a body, in the same way that Forward and North are completely different.. if you were to continue absolutely forward, you would eventually gain altitude and end up in space.. North on the other hand is relative to the Earth and can become South if you continue far enough)