A number of deleted scenes from Avengers: Endgame have been made available on Disney Plus, two of them involving how the final movie was changed to explain its use of time travel.
It was previously established that the film’s rules of time travel don’t make complete sense, due to their being changed midway through production to justify Steve Rogers’ fate at the end of the movie, and even the writers and directors don’t agree on how the temporal and multidimensional mechanics were twisted to make the appearance possible.
The principal scene in question involves Banner meeting the Ancient One during the Battle of New York from 2012’s The Avengers, in the hope of convincing her to relinquish the Time Stone. It’d been previously stated that this scene was reshot to include the addition of the visualization illustrating how the removal of the Infinity Stones would create tangent timelines, along with the Ancient One’s explanation that the universe could suffer dire consequences should they not be returned.
In the original version of the scene, though, she states that “if you travel to the past from your present then that past becomes your future and your former present becomes your past, therefore you cannot be altered by your new future.” In the final cut of the film, this line was given to Banner to initially explain the theory surrounding how a person’s actions would be perceived in the timeline, essentially stating that their actions in the past will not affect the present to which they return.
Less significantly, the scene in the final cut of the film when Banner explains this was reshot from one that sees the quantum suits being constructed by Banner, Nebula and Scott before being tested by Hawkeye, with the change providing the audience with an explanation of how the logic of time travel would operate before it was used and give them a better idea of what to expect.
Crucially, the initial idea to wait until the Time Heist was underway to explain that past actions wouldn’t affect the present, implies that the Avengers could have initially believed that simply removing the Infinity Stones from the past would have prevented Thanos from collecting them, thereby making the story’s resolution far simpler and not requiring an epic and poignant climactic battle sequence to end it.
Anyway, as with most tales involving time travel, the minutiae of how it functions is largely irrelevant, since the concept is currently understood to be impossible and generally only serves to be used as a plot device rather than a discussion of quantum mechanics. Practically, its use in Avengers: Endgame worked out the same, but the order of the unveiling of information made a significant difference in how it played from a narrative perspective, with the changes arguably being made for the best.
