All the major 'Avengers 4' theories that have the best chance of coming true

"Infinity War" directors Joe and Anthony Russo have implied that when Thanos killed his adopted daughter Gamora, her soul entered the Soul Stone. When Thanos snaps his fingers to eliminate half of humanity in the universe, he wakes up in a dream-like place that the Russos have said emulates being inside the Soul Stone. It's here that he talks to a younger version of Gamora, who asks him what it "cost." He replies, "everything."

I never took the Russos' comments literally (plus, the comments were taken from a Reddit thread based on a high school visit where the directors reportedly took questions from students). I read it more as her being in the Soul Stone metaphorically, and Thanos waking up inside of it as a visual representation of his thoughts and fears after the snap. The "Infinity War" visual effects supervisor feels the same way, and said in an interview that it's "open to interpretation."

"It just seems like an internal moment of reflection," Kelly Port told CNET earlier this year. "It's this really nice dramatic pause at basically the culmination of 10 years of storytelling, right? It's this moment where he can just have this moment to internally reflect on what he's done and the cost of that decision."

If true, though, the theory may even account for where other characters went after the Thanos snap. If Gamora is in the Soul Stone, maybe half of humanity is, as well.

Captain America/Steve Rogers' fate was questioned before "Infinity War" was released, and since he survived that, his death is even more possible in the sequel. Out of all the original Avengers, Captain America's death would make the most sense.

Actor Chris Evans has implied that he is ready to retire from the role after "Avengers 4." The character died in the comic books after the events of the "Civil War" comic, so it wouldn't be a stretch for Cap to perish.

Furthermore, Cap's death would mean that the MCU has come full circle. He was the "First Avenger," and his death would mark the end of this era of the MCU and push it into a new one going forward. Ever since he was thawed from that ice and thrust into the 21st century, Steve Rogers has been a man out of time. He clings to a stubbornness that has made him a respected hero, but may also foreshadow his end. In "Infinity War," he refused to sacrifice Vision's life to destroy the Mind Stone. "We don't trade lives," he proclaimed. But the one life Captain America has shown he is willing to trade is his own.

One theory in particular gained traction recently on Twitter. It proposes that Cap will die and be reunited with his love Peggy Carter. The tweet has 19,000 retweets and 97,000 likes. In "Captain America: The First Avenger," after he is thawed out, he tells Nick Fury that he's late for a date — maybe he'll finally show up for it.

There are a number of ways this theory could be true. The most obvious is there is an Infinity Stone that controls time. If the Avengers can gain possession of that, then there's a chance they can reverse the Thanos snap. Doctor Strange, the former keeper of the Time Stone, saw millions of possible futures in "Infinity War" and in only one did the Avengers defeat Thanos. Strange is obviously playing the long game, as he gives up the Time Stone to Thanos and later tells Iron Man that "there was no other way." Strange knows something that nobody else does, and he risked giving the stone to Thanos even though he probably knew he and half of humanity would be eliminated.

Another theory involving time travel has to do with the Quantum Realm seen in the "Ant-Man" movies. In the after-credits scene of "Ant-Man and the Wasp," Ant-Man is trapped in the realm after Wasp, Janet van Dyne, and Hank Pym vanish from the Thanos snap. Before he enters, Wasp tells Ant-Man that if he gets trapped in a time vortex, they won't be able to save him, so people must be able to time travel there.

Spider-Man actor and notorious spoiler Tom Holland seemed to confirm this theory in an old interview, in which he said that Strange actor Benedict Cumberbatch had to refer to the Quantum Realm a lot. The Quantum Realm never came up in "Infinity War," leading many to theorize that it plays a large role in "Avengers 4."