After the latest batch of set photos, it seems unavoidable that Avengers 4 is a time travel film. Marvel visionary Kevin Feige has described next year's outing for Earth's Mightiest Heroes a "finale" for the MCU. It will draw together countless plot-threads, ending a story that's spanned (by that point) 11 years and 22 films. For all that's the case, the movie remains something of a mystery. Marvel won't even announce the title, considering it to be something of a spoiler.Avengers 4 was originally intended to be a follow-on from this year's Avengers: Infinity War, with it even dubbed "Part 2" upon announcement. Of course, something changed in early development, with the Russo Brothers later teasing that the films would be closely connected ” but also very different: "The first movie is very clearly Avengers: Infinity War," Joe Russo explained, "and, in time, we will reveal what the second film is."RELATED: Every Character Confirmed For Avengers 4That statement left fans intrigued, and from that point on every set photo has been examined with a sense of fascination. Why isn't Avengers 4 a straightforward sequel? How are the two Avengers movies connected, and in what ways do they differ? Marvel, for their part, have kept pretty quiet about the film. They've clearly enjoyed cultivating this sense of mystery and intrigue.But, finally, the evidence has come to a head. It's now possible to say for certain that Avengers 4 is actually a time-travel story. If that's the case, it hints at the final outcome of Infinity War ” and even explains one of Marvel's most longstanding mysteries.Why Avengers 4 Is Clearly A Time Travel Story (This Page)

Why Avengers 4 Is Clearly A Time Travel Story

Avengers 4 began filming in August last year, picking up straight after Infinity War, and it didn't take long for set photos to hit the Internet. Many of these showed characters suited up in classic costumes, harking back to 2012's The Avengers: Chris Hemsworth was seen sporting his flowing golden locks; Chris Evans was spotted wearing that "old-fashioned" costume. One set of images even showed Loki in chains being led away for his imprisonment in Asgard.

Other set photos and casting calls suggested there would be more flashbacks. Evangeline Lilly dropped a set photo showing her hair in a bob; while Hope Van Dyne wore her hair in that style in Ant-Man, set photos have confirmed she's ditched it by the time of Ant-Man and the Wasp. Chris Evans was snapped filming a scene set in the past, as he walked down a street filled with classic cars. A photo of Robert Downey Jr. showed him wearing a S.H.I.E.L.D. tactical vest ” an organization that is now defunct. Marvel casting calls included an appeal for actors to play an office scene set in the '60s.

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Finally, there's evidence that characters who have long been dead will actually be returning in Avengers 4. There have been rumors Frank Grillo would reprise the role of Crossbones, for example. Those were apparently confirmed when Grillo, alongside Marvel stars such as Chris Evans and Robert Downey Jr., attended an event in Atlanta. They were also accompanied by Maximiliano Hernandez, who played the late Agent Sitwell (killed in Captain America: The Winter Soldier).

At first, fans simply couldn't make sense of this. Why would the film have so many flashbacks? And, frankly, why would some of them be so random? Then, recently, Just Jared released their latest batch of set photos, showing Chris Evans on set with Paul Rudd. What's conspicuous is that Rudd is suited up as Ant-Man, while Evans was once again sporting the outfit he wore in The Avengers. There's only one logical conclusion: Ant-Man had clearly traveled back in time. More recent set photos have shown members of the cast holding some sort of timepiece device, adding further confirmation.

What Does This Mean For Avengers: Infinity War?

Fans are expecting Avengers: Infinity War to be a film like no other, with pretty much every MCU hero uniting to battle a common enemy. The first trailer gave a sense of Thanos's power, showing him one-punching Iron Man and pinning Spider-Man to the ground, although footage shown to fans at last year's D23 and San Diego Comic-Con went even further. It revealed Thanos wielding the power of the Infinity Stones, literally tossing comets at the Avengers. It's hard to imagine how Earth's Mightiest Heroes could possibly defeat the Mad Titan.

Related: Avengers: Infinity War Trailer Confirms Where The Final Stone Is

If Avengers 4 is a time-travel film, then it's possible the Avengers will not defeat him. Instead, some of their number ” most likely including Ant-Man ” will launch a desperate quest to rewrite history. They'll travel back to the past, perhaps seeking key moments that involve Infinity Stones. The Battle of New York is one such moment. After all, two Infinity Stones are in close proximity at that time; the time-travelers would be able to gain possession of both the Mind Stone and the Space Stone at once.

How Could The Avengers Travel In Time?

All this is fine, in theory. But how is it possible for the Avengers to travel back to the past like this? There are actually two possible ways.

The first is through the use of the Time Stone. As we saw in Doctor Strange, the Time Stone can be used to literally rewrite the past. With the Infinity Stones in play, it would make sense for the future Sorcerer Supreme to lend a hand by using this cosmic power once again. Unfortunately, set photos have strongly suggested Doctor Strange will lose possession of the Time Stone. In one sequence, Strange lies, defeated, as Ebony Maw plucks the Infinity Stone from the Eye of Agamotto. Given Ebony Maw betrayed Thanos in the comics, this doesn't necessarily mean Thanos himself will have acquired the Time Stone by the end of Infinity War, but it certainly complicates matters.

The second possibility, however, is through Ant-Man and Captain Marvel. Both heroes are tied to a mysterious dimension known as the "Quantum Realm." When Ant-Man shrinks beyond subatomic level, he enters a mysterious reality in which time and space are irrelevant. This year's Ant-Man and the Wasp will revisit the idea, with the heroes rescuing the original Wasp from this intriguing dimension. Meanwhile, quantum physicist Dr. Spiros Michalakis, a Marvel consultant, confirmed that the Quantum Realm will also appear in 2019's Captain Marvel. It's entirely possible that the Quantum Realm is outside the normal flow of space and time, and that Ant-Man and Captain Marvel can use it to travel to the past. No doubt it will be difficult to navigate this dimension, perhaps explaining why so many other time-periods play a role.

RELATED: Where Marvel's Infinity Stones Are After Thor: Ragnarok

The recent set photos have suggested that Ant-Man will be one of the time-travelers. And Kevin Feige recently teased that Captain Marvel would be essential setup for Avengers 4; he explained that the film would be "a big part of heading towards this epic conclusion and epic finale of 22 movies over the course of 10 years." With both films featuring the Quantum Realm, this definitely seems to be a likely method for traveling in time.

If Ant-Man and Captain Marvel do indeed use the Quantum Realm to rewrite history, it would explain one final Marvel mystery. Just why has Marvel slotted Ant-Man and the Wasp and Captain Marvel in-between Infinity War and Avengers 4? The answer, it seems, is because they're essential setup for Avengers 4. These two films will explore the Quantum Realm, helping viewers understand what it is they're about to experience in Avengers 4.

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It seems the future of the MCU will be decided in its past, and at this point nothing could be more appropriate. 2012's The Avengers was the centerpiece of the MCU to date, its release the moment the whole MCU project could have fallen down like a stack of cards but instead flourished. In-universe, the Battle of New York bound the heroes together, revealing the Avengers to the world. It's not an exaggeration to say that everything after is because of this one event. Now, it seems, Earth's Mightiest Heroes will return to the day of their greatest victory, and attempt to rewrite history to ensure they triumph once again.

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