When Avengers: Endgame brought time travel into the Marvel Cinematic Universe for the first time, the writers of the film wanted to bring a unique flavor to such a genre. After films such as Back to the Future, Looper, Terminator, and others have spawned their own unique rules for time travel, Christopher Markus and Stephen McFeely admit they may have modeled aspects of their rules after elements of Harry Potter and the Prisoner of Azkaban.
"We went back and watched both Back to the Future and Back to the Future 2, specifically," McFeely says of his teams preparation for Endgame. "But you can already predict why we did this, right? If we were gonna go back and follow time travel [rules], call them normal, it also tells how important Back to the Future is. Everyone thinks that that's how time travel works because that's a great movie, maybe the best of its subject. If we were do that, to do something in the past and it's gonna screw up your future, we're gonna do that six times. We would have no way to follow that. It would just be exponentially crazy town."
In fact, it was the third act of Harry Potter and the Prisoner of Azkaban which resonated with McFeely the most while running through time travel theories in film. "I do love, see, that third Harry Potter movie, where a stone will break a vase. You don't know why and the scene's fine and it doesn't take you out of it," McFeely said. "Then when you come back around and you realize that they had thrown it at themselves, I do love that."
Of course, if Avengers: Endgame were following these rules of time travel, it would indicate that there were doubles of characters like the Hulk, Iron Man, and Captain America in the Battle of New York from 2012's The Avengers. McFeely admits if the studio "had all the money in the world" and knew where the Infinity Saga's ship was landing, they may have planted seeds for these time travel elements back in that film. However, Markus points out that it "hadn't happened yet" before ruling that all of the theories can ultimately become a headache. "Immediately, you get into mind bending the paradoxes of time travel and it's best not to go there," Markus said.
Ultimately, the team decided not to follow the Back to the Future rules but to create a bit of their own as a means to preserve the MCU's narrative and challenge the Avengers heroes like never before. "It would also make solving their problem actually remarkably easy," Markus said. "They would just go back and knock over a water dish and suddenly time is changed and there's no disaster. We needed it to be the hardest thing that they've ever done."
Avengers: Endgame is available on digital downloads on July 30 and on blu-ray on August 13.