SPOILER WARNING: Big time spoilers follow for Ant-Man and the Wasp, so come back after you've seen the movie!
The year is barely past the halfway mark and we've already gotten three Marvel movies in theaters. The latest, Ant-Man and the Wasp, is fairly standalone, so those looking for an immediate follow up to Avengers: Infinity War may be disappointed. Though the light-hearted sequel doesn't try to have much to do with Infinity War, it still helps set up Avengers 4. It's long been rumored that Avengers 4 will deal with time travel, and the first post-credits scene in Ant-Man and the Wasp helps set some clues as to how the Phase 3 finisher could do this.
At the end of the sequel, Ant-Man enters the Quantum Realm to acquire some quantum energy, which is implied to be for the former villain, Ghost. However, Ant-Man's journey into the other dimension happens to coincide with Thanos' now-iconic snap. Hope van Dyne, Hank Pym, and Janet van Dyne are all dusted, while Scott Lang is left stranded in the Quantum Realm with no one available to help bring him back.
This scene is obvious set-up for Avengers 4 in the sense that it explains how Ant-Man survives the snap, but it also drops some other clues as to how he could contribute to the long-rumored use of time travel in Avengers 4. Before entering the Quantum Realm, Janet lists a series of dangers for Scott to avoid while he's inside, but the one that sticks out the most are Time Vortexes. There's no real elaboration on what that means, but it doesn't take a quantum physicist to figure out that it involves time travel. Assuming that Scott can't escape by just growing bigger like he did in his first movie, then the Time Vortex is the No. 1 theory right now.
How exactly time travel is supposed to play out in Avengers 4 is top secret, but that just makes it more attractive to sneaky photographers. Some set photos have been doing the rounds for a while and they show off Steve Rogers, Tony Stark, and Scott Lang in what appears to be the Battle of New York from the first Avengers movie. Aside from the war torn city streets, Steve is wearing his Avengers costume, which is a good indicator of when this scene takes place. If you can remember back that far, Scott wasn't even Ant-Man yet when this movie happened, so it feels safe to assume that he used something like a Time Vortex to escape the Quantum Realm and ended up in the Battle of New York.
HOWEVER! In those same set photos, Tony Stark is looking a little grizzled, sporting grey-ish hair. He didn't look like that in The Avengers, so it's possible that this is a Tony Stark who came back to the past from the future. If this Tony is also a time traveler, then there are questions about what is going on. Is his meeting with Scott just a total coincidence or is there a lot more going on here? To understand that, we need to consider there's another option in how Ant-Man potentially uses the Time Vortex.
It would make a lot of sense that Scott wouldn't be able to control what time period the vortex drops him in. So, if the vortex takes him to the Battle of New York, it must logically also be able to send him to the future, as well. Another popular Avengers 4 theory is that the movie takes place several years after Infinity War. If that's the case, then Scott could wind up in this future timeline with little to no time passing for him. From his perspective, it likely wasn't, say, five years since the events in Infinity War, and he would have no way of knowing about the snap and all the people who disappeared. This would also be a nifty way to explain the rumors about how his daughter, Cassie, will be a teenager in the movie.
We know the heroes are in desperate need of a plan to stop Thanos. Perhaps Ant-Man shows up out of the blue, having discovered a new means of time travel. Tony Stark gets to tinkering and (perhaps using Hank Pym's notes) finds a way to control the Time Vortexes in the Quantum Realm. For whatever reason, he chooses to go back to the Battle of New York and brings Ant-Man because he's the only one to have time traveled before.
It's important to remember that no one alive knows that Scott was in the Quantum Realm during the snap, so as far as the Avengers are concerned, he was dusted like half of life elsewhere. Unless someone accidentally finds him, Scott will have to escape the Quantum Realm on his own. Time portals seem a pretty good way to do that, but with a movie as mysterious as Avengers 4, many things are still possible at this point. We'll have to wait to find out when Avengers 4 hits theaters on May 3, 2019. In the meantime, take a look at what Marvel has coming up.