Harry Potter Theory
This theory is going to be about the third movie, Harry Potter and the Prisoner of Azkaban.
In the movie, Hermione possessed a time turner.
When she went back in time with harry, she said that they couldn't let the past them see the current/future them.
According to the movie, when you go back in time you create a copy of yourself, only one copy. When Hermione and Harry when back in time you could only see two of them.
This is where another theory comes in, the multiverse theory. (Stewie quote) The theory states that there are an infinite amount of universes coexisted with ours on parallel dimensional planes.
Sense you only see two copies of Hermione and Harry, that means they only went back in time once. When they when back in time, they created another universe.
The first universe is the one where did not go back in time.
The second universe is the one where they did go back in time.
So, every movie past the third one is in the second universe.
(This is my first theory, so sorry if it was short or bad.)