Avengers: Endgame served as the culmination of the Marvel Cinematic Universe as knew it. Twenty-some movies later and fans finally got a definitive ending to the story Marvel Studios had unfolded over the past ten years. Despite it being a concrete endcap to the majority of movies that came before it, it managed to squeeze out a few plot threads that weren't answered, allowing filmmakers in the future to pick the pieces up and run with them as they see fit.
One of those introductions includes the usage of time travel, something that had been unheard of in the MCU prior to the events of Endgame. As explained to us in the three-hour movie, it's a pretty simple science behind this particular time-traveling ruleset. Unlike Back To The Future or many other time-traveling movies you're aware of, characters in the MCU don't have to worry about a butterfly effect. They're unable to change the current timeline's future by going back in time; rather, when they go back in time, that splits off into an all-new timeline where an entirely new future can unfold.
It's because of that reason one new intriguing fan theory suggests Doctor Strange in the Multiverse of Madness has already happened. As pointed out by u/gunnersawus, Endgame created a minimum of five separate timelines as a direct result of events happening in the film, meaning the multiverse is already created and waiting for chaos to unfold.
Using this theory, that would mean Doctor Strange in the Multiverse of Madness wouldn't be about a trip between dimensions or worlds — instead, it'd be about the Sorcerer Supreme traveling amongst timelines in hopes of ironing out the kinks so the multiple timelines don't somehow manage to fold in on themselves.
If we want to get even more technical, Strange himself had previously seen how the Avengers win, meaning it's all but guaranteed he saw they traveled through time and created half a dozen new timelines in the process.0comments
Doctor Strange in the Multiverse of Madness is due out May 7, 2021.
Upcoming Marvel Studios projects include Black Widow on May 1, 2020, The Falcon and The Winter Soldier in Fall 2020, The Eternals on November 6, 2020, Shang-Chi and the Legend of the Ten Rings on February 12, 2021, WandaVision in Spring 2021, Loki in Spring 2021, Spider-Man 3 on July 16, 2021, What If…? in Summer 2021, Hawkeye in Fall 2021, Thor: Love and Thunder on November 5, 2021, and Black Panther 2 on May 6, 2022. Marvel Studios Disney+ series without release dates include Ms. Marvel, Moon Knight, and She-Hulk.