Multiversal incursions are the new hotness in the Marvel Cinematic Universe: one of the numerous ongoing dangers to creation resulting from the release of the Multiverse during the events of the Loki streaming series on Disney+. An incursion takes place when two or more realities collide into each other, with vague yet dire implications for both. It’s served as the central threat – in one form or another – for both Spider-Man: No Way Home and Doctor Strange in the Multiverse of Madness, as well as playing a key role in a number of other MCU projects.
And yet the rules governing incursions haven’t been well-defined, at least not yet. As dangerous as they are, there are several big exceptions, whose reasons for escaping the concept’s doomsday ramifications aren’t always clear. The MCU hasn’t cleared up the issue as of The Multiverse of Madness, though with Phase 4 ongoing that’s very likely a matter of timing rather than negligence. Even so, the cause of incursions remains frustratingly vague, as are the qualities that separate them from less destructive cross-reality travel. A definitive reason for them has not yet been determined, though fan theories, as usual, have made some compelling arguments.
The Multiverse in the MCU sprang to life during the events of Loki Season 1, Episode 6, "For All Time. Always." Loki’s female variant, Sylvie, murdered He Who Remains, who kept reality under tight wraps with a single "sacred" timeline encompassing the whole of creation. He warned both Sylvie and Loki of the dangers of the Multiverse, which included the rise of reality conquerors like Kang and the variant Ultron from the What If…? animated series. But they were far from the only dangers, which subsequent MCU projects quickly proved.
The threat in Spider-Man: No Way Home was reasonably diffuse, but provided a good case study of the kinds of things He Who Remains was talking about. The collection of Spidey’s rogue’s gallery from multiple franchises – as well as the arrival of the two previous cinematic Peter Parkers to fight them – were the precursor to a possible infinite number of similar figures, which would doubtless have overwhelmed the confines of the main MCU (Earth-616) had Spidey not closed the breach at great personal cost. The Multiverse of Madness confronted the issue more directly, with the Illuminati of Earth-838 explaining the dangers of a possible incursion. Doctor Strange and Christine discovered an object example soon thereafter: a reality undone by a collision with another.
And yet copious evidence exists of numerous supposed incursions resulting in no damage whatsoever. The most obvious is America Chavez, who has spent years jumping from reality to reality without effect to either her or them. Earth-616’s current incarnation of Gamora is a variant, and she too has spent a good deal of time in a new reality without apparent difficulty. And The Watcher from What If…? finished Season 1, Episode 9, "What If… the Watcher Broke His Oath?" by sending a variant Black Widow from an extinct reality to a new one, where she saves the day and presumably continues her journey.
All of that has thoroughly muddied the question of incursions, and more importantly what causes them. The comics provide a few clues, though it’s uncertain whether the MCU will follow through on their logic or not. 2013’s New Avengers Vol 3 #2 spells out the specifics, stating that they’re caused by a "contraction" of the Multiverse, resulting in two or more separate realities colliding. Each incursion lasts eight hours and ends with the destruction of both universes. A number of methods can prevent this, including the destruction of one universe before they both go. Fan theories on Reddit have pointed out ways in which that notion can be ported over into the MCU. That includes the killing of a variant by another variant – which Molecule Man did in the comics to create an incursion – and copious dreamwalking, which The Multiverse of Madness stated was dangerous in and of itself.
Which explanation the MCU will use, or whether it will do so in a manner that makes sense, has yet to be seen. The Multiverse is a dramatic device first and foremost, and at the end of the day, the franchise will use whatever explanations it needs to in order to tell a good story. But the questions demonstrate how tricky it can be to introduce concepts like incursions to a large, complicated universe, and how readily the MCU can back itself into serious continuity problems if it isn’t careful. The Reddit theories suggest solutions are available, and the franchise has been good about adding new rules to its universe with proper forethought. Time will tell whether and how well this particular knot gets untangled.
Doctor Strange in the Multiverse of Madness is currently playing in theaters.