(Note: This post contains a ton of spoilers for "Avengers: Infinity War," especially the ending, obviously. Read on at your own risk!)
If you've been theorizing that the still-untitled "Avengers 4" will undo the shocking events of "Infinity War" by having the Avengers perform a reverse version of Thanos' finger-snap, belay that. "Infinity War" co-director Joe Russo seems to have ruled that out entirely.
The question as the credits roll on "Avengers: Infinity War" is a giant "what the hell happens now?" Moments before the end credits, Thanos finally completes his quest to gain possession of the six incredibly powerful Infinity Stones and he uses their power to kill half of all life in the universe. (He's a fanatic who believes that murder on this scale will solve all future resource shortages.)
That death toll includes more than half of the existing Marvel Cinematic Universe, like Spider-Man, Doctor Strange, T'Challa, and many more. The reason Thanos was able to do it is that he wore a specially-made metal glove, the "infinity gauntlet," on which he placed the six infinity stones. The gauntlet allowed him to combine and channel the power of the six Infinity Stones without being destroyed by them.
But according to Joe Russo, that trick only works for Thanos, himself. Speaking on Josh Horowitz's "Happy Sad Confused" podcast, Russo said that the only reason Thanos survived using the gauntlet in is because of he's so incredibly powerful.
In fact, Thanos only barely survives. His entire left side is injured when he snaps his fingers, the Gauntlet itself is hugely damaged, and he's briefly sent into the orange-hued Soul World where he encounters the spirit of Gamora (Zoe Saldana), his adopted daughter, who Thanos sacrificed in order to get the Soul Stone.
"I think it's a reflection of [Gamora's] spirit, and the power required to use all of the stones at once is so significant that it sends Thanos into this dream state," Russo said, via Collider. "You'll notice his arm is damaged post the snap, the gauntlet is damaged post the snap, it's the incredible energy required from it and only because of his strength is he able to survive actually using the gauntlet in that capacity."
If Thanos is the only one powerful enough to survive using the Infinity Gauntlet and the six stones at the same time, that could have some serious implications for what fans are predicting for "Avengers 4." While losing half of all the characters in the film was a gut-punch of an ending, nobody really expects it to stick. After all, Marvel Studios has already announced "Guardians of the Galaxy Vol. 3" as well as follow-ups to "Spider-Man Homecoming" and "Black Panther," the leads of all three disappeared when Thanos snapped his fingers. There's going to be some way to undo the damage Thanos has done, and everyone is wondering what that might be.
In the Marvel comics version of the "Infinity War" story, "Infinity Gauntlet," it's Nebula (played by Karen Gillan in the movie) who gets the gauntlet away from Thanos in a moment of weakness and uses it to briefly control the universe. Working with the heroes after they convince him that he was terrible, Thanos tricks Nebula to undoing the snap by reverting the universe to its state 24 hours earlier. Then the good guys get the gauntlet away from her and separate the Infinity Stones to minimize their power.
Lots of people have theorized that this is the solution that makes the most sense, although other fan theories abound. With elements like the Time Stone in play, the heroes could potentially undo Thanos' actions or even travel back in time to stop him earlier. But if Thanos is the only person in the MCU -- or at least, who has been revealed so far -- powerful enough to use the Infinity Gauntlet without dying, that could have serious implications for the theory that some other character could use the gauntlet in "Avengers 4." It suggests three main possibilities for how the Thanos situation could be resolved, if the Infinity Gauntlet is the only solution:
1. A character as powerful as Thanos has to show up in "Avengers 4"
This is a possibility, and there's precedent for it in the comics. In that story, it's the cosmic character Adam Warlock who helps out the heroes and winds up with the Gauntlet after using his connection with the Soul Stone to force Nebula to take the Gauntlet off. However, while Warlock was teased in the post-credits scene of "Guardians of the Galaxy Vol. 2," Marvel has so far said that the character won't show up in the MCU until "Guardians of the Galaxy Vol. 3." Then again, Marvel has been known to bend the truth to throw fans off and preserve surprises. (Here's what happens next in the Marvel comics version of the story.)
2. A hero will use the Infinity Gauntlet and die in the process
This one fits current expectations for "Avengers 4." The snap might get undone to save the people of the universe, but not everybody is going to make it out alive. The most obvious candidates are Captain America (Chris Evans), Thor (Chris Hemsworth), and Tony Stark (Robert Downey Jr.), all of whom are only contracted through "Avengers 4." Evans in particular has signaled that he's ready to move on from the role of Cap, so he'd probably make a solid candidate for the hero who winds up killed by the Infinity Gauntlet it order to use its power to save everyone else.
2.5. Multiple heroes will use the Infinity Stones
This is a possibility hinted at in the original "Guardians of the Galaxy," when The Collector explains what Infinity Stones are. Apparently at some point in the distant past, a group of beings managed to share the power of the six infinity stones between them, and were destroyed by it. At the end of that film, the Guardians themselves manage to share the power of a single Infinity Stone between them, and barely survive.
You can guess where we're going with this. There are six stones, and more than six major Marvel characters who survived "Infinity War." Including all six original Avengers -- Thor, Black Widow, Captain America, Iron Man, The Hulk, and Hawkeye.
3. The heroes will have to convince Thanos to undo the snap
This also feels very possible just because "Infinity War" follows Thanos more than any other character, exploring his fanatical beliefs in detail and frequently juxtaposing him to the heroes. Where every other character is willing to give up Infinity Stones to save the lives of their friends, Thanos murders (discriminately, however) and sacrifices everyone he cares about to attain their power.
But especially after the loss of Gamora, Thanos seems to feel some serious remorse about what he's done. If the heroes can convince him there's a better way -- maybe by increasing the universe's resources instead of decreasing its life, or just accepting that policy has as much to do with scarcity as resource supply -- he might be willing to use the Infinity Gauntlet to undo everything himself. Who knows if he'd survive it a second time, though.
Of course, this is all just a lot of speculation about what could happen, but it does seem important that the Infinity Gauntlet isn't easily wielded by regular people, or even superheroes. "Avengers 4" will answer the question definitively in May 2019, but it's likely that the two MCU movies launching before then -- "Ant-Man and the Wasp" in July and "Captain Marvel" in March 2019 -- will also have an impact on the situation before it's all resolved.
We've spent a lot of time over the past few weeks digging through the details to try to figure out what's coming not just in "Avengers 4" but also "Captain Marvel" and "Ant-Man and the Wasp." We have come up with a pretty solid guess about what is involved in the one future Doctor Strange saw in which the Avengers defeat Thanos. Click here for our deeper look into how "Captain Marvel" might impact that distressing plot twist at the end of "Infinity War." Click here for our look at what "Ant-Man and the Wasp" might have to do with all this. Click here for our discussion of the whole Vision situation and whether he's really dead. Here's a rundown of how "Infinity War" could actually be a giant, elaborate test. If that's not weird enough for you, here are some other wild fan theories. And, finally, here's our run-down on how the comic book version of these events played out.