Warning: SPOILERS for Avengers: Infinity War are ahead!
The intrepid heroes of the Marvel Cinematic Universe have been through a lot over the last decade, but it's safe to say that Avengers: Infinity War marked their biggest defeat yet. Despite their best efforts, the Avengers, Guardians of the Galaxy and the other protagonists involved were unable to stop Thanos from obtaining the six Infinity Stones, and with the snap of his fingers, the Mad Titan wiped out half of life in the universe. It was definitely the most depressing MCU movie ending yet, and we still have a little less than a year to go until we find out how this arc wraps up in Avengers 4. Officially, Marvel Studios is keeping specific details concerning Avengers 4 close to the proverbial chest. Unofficially, certain details have come to light hinting that Avengers 4, as impossible as it may seem, will be even crazier than Infinity War.
Since late last year, numerous set photos have popped up showing that Avengers 4 will be re-visiting key moments in MCU history. Arguably the most notable of which is The Battle of New York from 2012's The Avengers, which saw Earth's Mightiest Heroes officially forming as a team for the first time. It will be a while until Marvel Studios sheds light on the context of these scenes, but fortunately there's been no shortage of speculation on how these moments are even possible.
This all started back in October, when Hayley Atwell, best known for her portrayal of Peggy Carter, mentioned on social media that she was in Georgia, where both Avengers: Infinity War and Avengers 4 were shooting for all of last year. Atwell's more recent comments indicate that another Peggy appearance might not be as set in stone as some fans assume, but then set photos uploaded in November showed 1940s-era cars, indicating that we would indeed be going back to the Captain America: The First Avenger era. Granted, working off that alone, it's possible that Avengers 4 might simply be flashing back to the years that Steve Rogers originally hailed from. Then things got more interesting.
Last December, stunt performer Heidi Moneymaker (best last name ever) posted pictures on Instagram showing Scarlett Johansson wearing the same clothes and rocking the same hairstyle that she had at the beginning of Captain America: Civil War, when Black Widow and some of the Avengers were in Lagos, Nigeria to apprehend Brock Rumlow, a.k.a. Crossbones. This followed a report months earlier that Frank Grillo had been seen on the Avengers 4 set. So rather than Crossbones being miraculously resurrected, we would be seeing him as he was in Civil War. Finally, we come to the Battle of New York pictures, which originally showed up in January and have been making the rounds again in recent weeks. Some of them shows Chris Evans wearing the same Captain America uniform he had on in The Avengers. Paul Rudd's Ant-Man and Robert Downey Jr's Tony Stark were also in the scene, although Tony had blonde-tinted hair and was wearing a S.H.I.E.L.D. jumpsuit. Oh, and there were other pictures showing Mark Ruffalo wearing a motion capture suit and carrying a giant bindle, which is... just weird. In any case, along with Avengers 4's present day events, the movie will also be messing around with the past, which leads us to the first theory about how this is possible.