Message of Movie explained

Rating: 10/10 (26 June 2018)

First of all wanna say amazing movie.. really incredibly visceral.. but for anyone confused this is what I gathered :P The universe is in flux. It expands, then contracts, replaying and recreating events over and over again. However, certain events can be changed, and depending on the choices Nemo makes his life will turn out different ways. The major turning point in his life being his decision to either go with his mother or his father at age nine, which is why in the end he says its all in the mind of a nine year old boy. He knows the choice he has to make and the myriad of possibilities it could lead to. In a way he's God of his own world at that moment.
But how does this happen? Think back to.when as a child he describes the place where babies are made. Before sent out into the world you know everything, but your mind is erased at birth. His never was, which is why he can predict the future at certain points in the film, why as an old man he remembers his life different ways.
In the end, when everything is reversing thats the universe contracting, resetting everything to be done again. The universe contracts at the exact moment of Old Nemo's death. Since he's lived it multiple times he remembers it and it features in the science fiction story he writes.
As to how he ends up with Anna, the universe is in a perpetual state of fluctuation, repeating itself forever. Depending on the decisions he makes sometimes he ends up with her, sometimes he doesnt. What we saw was the result of a time when he ended up with her.