Spoilers ahead. As Marvel fans proceed through the stages of grief in the wake of Avengers: Infinity War, nothing soothes the pain like internet sleuthing. And one of the biggest theories to come out of the film has to do with what Doctor Strange’s plan in Infinity War might actually be. So far, the Marvel Cinematic Universe has explored different planets and different Realms, but it hasn't yet dived into different universes. But this Doctor Strange Infinity War theory shows that the sorcerer's grand plan to defeat Thanos once and for all might not only hinge on the fact that different dimensions exist alongside the one we’ve already seen, but rely on Strange already having messed with them in a serious way.
In Infinity War, Strange, a so-called Master of the Mystic Arts, sees over four billion different futures involving Thanos, and tells Tony Stark that the good guys only win in one of them. And, as we all know, the ending of Infinity War makes it seem pretty clear like the heroes lose, with half the world disappearing thanks to Thanos' infinity gauntlet. But as Strange disintegrates to dust, he reassures Tony that, “This was the only way," and the line makes it seem like the deaths were actually part of the sorcerer's master plan. As such, the quote has sparked several theories as to what exactly Strange's plan was that it required the sacrifice of half the universe to pull out a win. Well, there’s one obvious answer: the multiverse theory.
We’ve seen two major alternate universes in the MCU so far. In Ant-Man, the Quantum Realm was introduced as a dimension outside of time and space, which you can only get to through magic or through shrinking really, really small. As you can guess from both of those requirements, both Ant-Man and Doctor Strange have paid the Realm a visit, though only Ant-Man knew it for what it was. Meanwhile, in Doctor Strange, the Dark Dimension is introduced as, again, a place outside of time. Sorcerers can draw power from it to strengthen their spells and lengthen their lives, but an evil creature known as Dormammu resides in it, waiting to possess anyone who comes across him and conquer whatever dimension they come from. The Dark Dimension is but one universe that Doctor Strange is introduced to by the Ancient One, who says this gem of a quote:
"This universe is only one of an infinite number. Worlds without end. Some benevolent and life-giving; Others filled with malice and hunger. Dark places, where powers older than time lie... ravenous... and waiting. Who are you in this vast multiverse, Mr. Strange?"
Essentially, both the Quantum Realm and the Dark Dimension are just two of the many, many multiverses that exist at the edges of the MCU — and Doctor Strange knows that. Thus, his grand plan to defeat Thanos could be that the heroes of this universe aren’t enough, but the heroes of other universes might be. But how to get them to our universe? After all, traveling to another dimension is said to be incredibly difficult; going there seems to be a lot easier than coming back in one piece. Scott Lang’s memory didn’t even survive his trip in Ant-Man.
Well, there are three major ways that Doctor Strange could have already set the MCU up to receive visitors from other worlds in the second half of the War. First, one of the running themes of Infinity War is said by Steve Rogers: “We don’t trade lives.” What seemed like Steve being stupidly noble could have made up Doctor Strange’s key strategy. Like Thanos had to trade Gamora’s life for the Soul Stone, Strange could have had to trade half the universe’s lives — including his own — to allow for reinforcements from other universes to make their way through.
In other words, it was about generating energy or balancing the scales. So it’s possible that, instead of the footage of Ant-Man hanging out with the Avengers from the 2012 movie being evidence that he traveled back in time to erase the darkest timeline, Ant-Man actually traveled through the rift those sacrifices made in the dimensions to another universe.
Secondly, there’s the fact that in Infinity War, Doctor Strange does essentially nothing while the Guardians, Iron Man, and Spider-Man are trying to yank the Gauntlet off of Thanos’ arm. Sure, neither do Nebula or Star-Lord (ugh), but we barely even get a glimpse of Strange once they start trying to get the Gauntlet off. What is he doing? Perhaps he's setting up a spell that would open a gateway between universes.
In Doctor Strange, the sorcerer was revealed to not only have a photographic memory, but to steal books from the library and use astral projection to read all night while his physical body rested. The next time we saw him in Thor: Ragnarok, he had gotten so good at opening doors to other worlds that he dropped Loki in a pocket dimension where the baddie was falling for 30 minutes, all so he could have a conversation with Thor. Bringing people into his dimension from another would require a lot of time and energy (see above), but it can’t be said that Strange wouldn’t know how to do it.
Finally, there’s also the way that Doctor Strange hands over the Time Stone to Thanos. Although Strange warns Iron Man that he’ll let him and Spider-Man die to protect the stone, Thanos has barely even finished stabbing Iron Man before Strange gives in. And even more suspicious than that is the fact that the sorcerer summons the Time Stone out of nowhere to give it to Thanos — so where was he hiding it? Somewhere else on the planet, or did he pull that stone from another dimension to give the soon-to-come heroes an anchor for when they came through? And could the Time Stone from our dimension still be hidden somewhere safe, waiting for someone to wind back the clock? Say… in the Quantum Realm that we already know Ant-Man can get to?
So yup, it seems like Doctor Strange might've sacrificed half the universe’s population to bring in multiverse reinforcements — including alternate versions of the heroes we know and love — and Ant-Man is the key to setting everything right. All the pieces are there for the multiverse to become a real part of the MCU in a way it hasn’t before. It wouldn't even be surprising if Captain Marvel’s upcoming film revealed that she’s actually lived in one of these alternate universes all this time and is only now on her way to save ours — thanks to Dr. Stephen Strange.