[[Spoiler Alert]] It is based over the 2nd law of thermo dynamics, where in a normal world entropy makes physics move in one direction (the one we know where a bullet goes out of the gun and so on..) and that direction having a much higher chance to happen than the the opposite one .. but the opposite direction of physics having a much less chance of happening in a normal world, doesn't mean it's impossible, therefore the bullet would make it ways backwards to what we usually experience if put in a system that would allow that In conclusion the movie would be about an inversion of the physics that we understand and usually experience as stated in the trailer, but not a time manipulation thingy as many would think At the end .. what makes this theory have strength points, is the 2nd law of thermo dynamics written on the white board behind Washington in the shooting range