The events of Avengers: Endgame changed a lot for the Marvel Cinematic Universe, with some characters making their exit in one way or another, and a host of new concepts introduced via the film’s time-twisting story.
Just how much the MCU has changed is a matter of some disagreement, though. Theories abound as to the potential effects of all the reality-shifting activities that occurred throughout Avengers: Infinity War and Endgame. We’ve rounded up some of the wildest ones that could forever change the way we ride through Marvel’s ever-expanding cinematic universe.
Thanos created Galactus
Ever since Disney acquired the movie assets of 21st Century Fox, speculation has surrounded the studio’s plans for the X-Men and Fantastic Four, the Marvel superhero teams that were previously under the Fox banner. A fan theory suggests that Marvel might have found a convenient way to introduce one of the Fantastic Four’s greatest foes via Endgame — and by association, primed audiences for the Fantastic Four to enter the MCU, too.
As Reddit user UpwardSpiral00 explains it, Thanos was too smart not to have a “backup plan” for reducing the population of the universe — after all, even after he snapped the population in half, it would eventually return to the prior levels. That insurance policy could very well be the world-devouring entity known as Galactus, conjured into existence with the same snap that Thanos used to get rid of the Infinity Stones in Endgame.
Although there doesn’t seem to be any overt foreshadowing of Galactus’ introduction to the MCU in Endgame, the theory certainly makes sense — after all, Thanos wasn’t the type to tie all of his universe-changing plans to a single course of action.
Two Captain Americas
Steve Rogers’ decision to travel back in time during Endgame and live out the rest of his life in the past with Peggy Carter opened up all kinds of speculative doors when it comes to Captain America and the MCU timeline. One popular theory was seemingly confirmed by the film’s writing team, with Endgame co-writer Christopher Markus indicating that yes, Steve’s decision did indeed result in two versions of Captain America existing simultaneously in the MCU: The Captain America from Endgame that traveled back, and the Captain America from all of the prior films.
“I would like to believe that through some sort of bullshit time loop paradox — throw in the words you use when you’re bullshitting science in a movie: ‘some sort of quantum paradox’ — that there are indeed two Captain Americas in the MCU timeline,” said Markus during San Diego Comic-Con (as reported by Screen Rant). “That Steve Rogers who looped back into time has therefore always been there, and that he is living somewhere else in the movies you’re watching.”
This has led some fans to look for evidence of “old Cap” in scenes from earlier MCU films — and possibly finding it in Captain America: Civil War. During the scene in which Steve attends Peggy’s funeral, some eagle-eyed fans have suggested that both characters — the older, time-traveling Steve and the younger Steve we see in the film — are in attendance, and pointed to still images from the film as evidence.
The Immortality Machine
One particular scene in Endgame sparked a fairly wide-reaching theory to come out of the Avengers’ early attempts at traveling through time. At one point, Bruce Banner ages Scott Lang from a toddler to a senior citizen, then back to his original age, while working out the kinks in the team’s time-travel machine.
As Reddit user ak2sup points out, the aging and de-aging effects of the machine were unintentional and made for a good comedic moment, but they could also be put to use in some ways that could affect the future of the MCU. For example, the machine could be used to de-age Steve Rogers and give anyone who uses it regularly a sort of immortality.
It’s a particularly interesting theory when you consider the implications of such a machine when considering Tony Stark’s fate.
Scarlet Witch won
One of the most mind-bending theories to come out of Endgame suggests that an entirely new timeline was created during the events of Infinity War that has essentially split the MCU into at least two distinct universes.
When Bruce Banner goes back in time to retrieve the Time Stone from The Ancient One in Endgame, she explains to him that every instance in which someone changes the past creates a new timeline: One in which events transpire without the past changing and one in which new events unfold as a result of the change.
This is particularly important given the events of Infinity War, in which Scarlet Witch reluctantly uses her powers to destroy the Mind Stone (and in doing so, her Avengers teammate Vision) in order to prevent Thanos from acquiring all of the Infinity Stones. Her attempt is successful and seemingly wins the day for the Avengers, but Thanos uses the Time Stone to reverse her actions and bring Vision back, only to then execute him and take the Mind Stone.
If The Ancient One’s explanation proves true, then everything that happens after Thanos turns back the clock is part of a new, alternate timeline in the MCU. One timeline includes the events that transpire after that moment in Infinity War and everything that follows in Endgame, while the other timeline — which includes all of the events leading up to that moment in every prior MCU film — has Scarlet Witch defeat Thanos’ plan and prevent him from gathering all of the Infinity Stones. (What happens after that point is a mystery, though.)
Given that Doctor Strange saw more than 14 million possible futures in which Thanos wins, it also seems safe to suggest that even if Scarlet Witch did destroy the Mind Stone, there’s a good chance that Thanos still found a way to see his apocalyptic plan through anyway.
The Stan-Steve Connection
Maybe the most unlikely theory, however, happens to be the one that’s also the most fun to consider.
Over on reddit, user MemTheDurgen explains how all of the cameos from legendary Marvel Comics creator Stan Lee in the MCU films could actually be time-displaced Steve Rogers. The theory suggests that everything Lee does in each of his cameos corresponds to something Steve Rogers might have said or done in those scenarios — meaning that Lee was actually portraying “old Captain America” throughout his appearances in the MCU.
“It makes sense for Steve to want to hang around his own exhibit [in Captain America: Winter Soldier] as a guard, telling people about himself discreetly,” reads one of the examples. “It could have also been a job to help pay for the medical bills of an ailing Peggy Carter who we see in this movie.”
Additional examples include Lee’s appearance in Avengers: Age of Ultron as a World War II veteran — a description that could be applied to Steve Rogers, too.