This Doesn't Mean The Avengers Can Reverse The Snap
At first glance, this theory seems very unlikely. After all, if the Avengers win early on in Avengers: Endgame, why does the film have a three-hour runtime? Surely they'll simply be able to reverse the snap, and if Thanos returns to Earth trying to get the Infinity Stones back he'll find himself opposed by the full force of the Avengers, complete with their resurrected allies?
Actually, that's not the case. On paper, the Avengers' plan is a sound one: get the Infinity Stones back, use them to undo the snap. In reality, though, it's a lot more difficult. For one thing, the Avengers know a lot less about the Infinity Stones than Thanos does, and there's no reason to assume they know how to use them - let alone how to use them in conjunction. What's more, precious few beings have the potential to wield a single Infinity Stone, let along six. As revealed in Guardians of the Galaxy, just touching the Power Stone dissolves most beings in a devastating explosion. When Ego heard of a human who could hold on to the Power Stone, he knew at once it had to be his son, a half-Celestial. We don't even know what would happen to anyone who touched the Soul Stone, or even the Time Stone. It's true that Captain Marvel could potentially be able to handle a couple of Infinity Stones, given her body is flooded with Tesseract energy, but she probably couldn't wield all six.
Then there's the fact that the Infinity Gauntlet itself is damaged as a result of the snap. The snap involved so much energy that even the Infinity Gauntlet, a device literally built to wield the power of the Infinity Stones together, couldn't cope with it. There was a backwash of energy that left Thanos' entire left side scarred. Indeed, Thanos' weakness - and the damage to the Infinity Gauntlet - may explain why the Avengers could succeed in stealing the Infinity Stones from the Mad Titan in the first place. But if that's the case, the Avengers won't be able to use the Infinity Gauntlet again, and even if they succeeded they'd risk dying in the attempt.
How This Fits With The Time Travel Theory
Given this is the case, it's entirely possible the Avengers will succeed in their first plan, getting the Infinity Stones from Thanos, only to learn they can't use them to undo the snap at all. In spite of all their efforts, in spite of all they'd lost, the Avengers would be forced to accept that they had failed; that half the universe had been killed on their watch. Their cause would seem to be hopeless.
Until, that is, they hit upon the second plan. There's strong evidence that Avengers: Endgame involves time travel, most likely through the Quantum Realm. This mysterious plane of reality is inspired by real-world theories of quantum mechanics, which posit that when you shrink to a subatomic level the laws of time and space break down, potentially allowing for time travel. The post-credits scene of Ant-Man & the Wasp left Scott Lang trapped in the Quantum Realm, but a potential escape was hinted at by Janet Van Dyne's mention of "time vortexes." The trailers for Avengers: Endgame have already confirmed that Scott Lang will indeed get out of the Quantum Realm, arriving in a post-snap world and rushing to the Avengers Compound - in the van containing the portable Quantum Tunnel. Finally, note that the Avengers have been shown wearing new white team uniforms, designs that are similar to Hank Pym's Quantum Realm environmental suits. It looks as though Ant-Man's arrival inspires the Avengers to consider a shocking new idea; if the snap can't be undone, perhaps it can be averted by rewriting history altogether? That, presumably, is where the film's second act begins.
Naturally, this is just a theory. The level of secrecy over Avengers: Endgame is absolutely unprecedented; but still, this is definitely a strong possibility, an attempt to put the different pieces of the jigsaw together and make sense of the picture. Only time will tell whether or not it's right.
- The Avengers 4 / Avengers: Endgame (2019) release date: Apr 26, 2019
- Spider-Man: Far From Home (2019) release date: Jul 02, 2019