what a great movie , I loved it , I enjoyed it a lot . the idea of time travel was really great , the movie pushes you to think and try to understand what is going on , it's like it forces you to focus and pay complete attention to put the pieces of the picture together and use your mind trying to guess what would happen next, if they could change the past or not . the last part of the movie reminds me with harry potter and the prisoner of azkaban movie when harry moves back in time and actually change the past . in the end of the movie , you will understand how the movie got its name when denzel meets paula and he doesn't recognize her when she knows him and he feels while talking to her that he is having a DEJA VU . I searched the internet on time travel and understood some parts related to it like if you want to go to the past you have to travel faster than the speed of light or you can use black holes , another thing I found was the theory of parallel universes, or alternative histories , I guess this is what the movie is based on , I'm not sure . anyway to understand this theory Let's say that you do travel back to meet your grandfather when he was a boy. In the theory of parallel universes, you may have traveled to another universe, one that is similar to ours, but has a different succession of events. For instance, if you were to travel back in time and kill one of your ancestors, you've only killed that person in one universe, which is no longer the universe that you exist in. And if you then try to travel back to your own time, you may end up in another parallel universe and never be able to get back to the universe you started in.
The idea here is that every action causes the creation of a new universe, and that there are an infinite number of universes that exist. When you killed your ancestor, you created a new universe, a universe that was identical to your own up until the time you changed the original succession of events. or maybe like Erika alexanderin the movie said , time is like a straight line in space along which events happen and if you changed one of these events by some how on a certain point , starting from that point the time line will give another branch with new successive events different from the original ones based on the change you have made . the whole thing is confusing and for me ,I don't believe we can change the past , what happened , happened you can't do any thing about it .
