Time travel is possible if you can travel faster than light.

For example: Start from earth now and go away to another glaxy with a speed greater than light. So you can see the light waves of incidents just happened are falling behind you. Now increase the speed very much and catch a light wave of an incident that was started from earth one year ago. Now return back to earth with more speed. You will be landing on earth with a time shift to past.

If you believe in multiple universes as the M theory states, there is no need to travel to space. You can travel to another universe just around you and return back through another door. You will reach a time shifted version of this universe.

Inorder to go to another universe, we dont have to travel to the boundaries of this universe. The universes are embedded within each other which I cant explain with our limited knowledge on dimensions.

Consider the following. You are watching a movie in a theatre. The hero in the movie is surrounded by terorists. They will surely kill him ( It is not neo in matrix ). So what is the only chance he has to survive. " He can step out from the movie screen in to the movie house ! ". Impossible ? That is m- theory saying about multiple universes. In that way, we can travel from one universe to another, without considering distance.

Now scientists are working very hard to achieve this. They are trying to send a "graviton" to another universe.

I can tell more on M-theory, if you want..