So in the movie, Carlin is investigating a terrorist incident in which over 500 people are murdered including a woman Claire who he becomes infatuated with. He ends up working with spooks who have a time machine that can see 4 days in the past. He discovers that when he flashes a laser pointer in one of the monitors showing the past that Claire responds to the flash. When Carlin starts to see that some of the events in the past are due to changes he made, that is when things start to happen. Many people guessed that there are two worlds. There is World-1 where events all happen that motivate Carlin to take the case. Then World-2 is created when he starts to alter the events of World-1. Carlin-1 eventually enters World-2 where there is also a Carlin-2. At this point, it is my belief that World-1 no longer exists. It did exist, but now it does not. There is only Carlin-2 and World-2. Carlin-1 could have returned to World-1. But that world isn't worth living in to him.