There are many theories for Time Travel.
The self-regulating theory in which Time "looks after itself" and you can never change the past.
The Alternate timelines theory in which if you go back and change the past you create a branch of time, in which a different universe now exists, side by side with the original.
There's also the tree theory or alternate dimensions stating that everything that could possibly has happened, and each choice/decision/possiblity spawns a new dimension.
The theory that you can change the past, and destroy the universe if you screw it up.
But the point is, that these are only THEORIES. Just because a movie demonstrated one, does not make it fact. Until we actually CAN travel through time, they will remain only theories.
Some other comments...
Newtons physics laws, although accurate enough, are flawed (This is what Einstein discovered and proved) particularly in regard to large mass' and speeds close to that of light. Therefore, the "every reaction has an opposite and equal reaction" law is not something I would necessarily put my money on in regards to time travel.
As for the stretching mentioned earlier, Einsteins theories said that the closer you get to the speed of light, the closer to infinity your mass becomes, the more stretched out you become, and the slower time gets.
This means that at the speed of light, you would be very heavy, very thin and not moving in time.
However, Einstein also theorised that it is impossible to travel at the speed of light, since it would require an infinite amount of energy to reach c (the speed of light).
I'm just informing you. These are theories that have held up so far.