How [Spoiler] Works in the Marvel Cinematic Universe

WARNING: This post contains extensive spoilers for “Avengers: Endgame” 

When it comes to explaining the mechanics of time travel in fiction, the precise methods, processes and consequences vary innumerably from one world to the next. What is true for Marty McFly is not necessarily going to be true for the crew of the Enterprise. With the release of Marvel Studios‘ “Avengers: Endgame,” audiences now have confirmation of the franchise’s approach to temporal mechanics. If you were left scratching your head about what it all means, don’t feel bad. Most of the Avengers seemed to have a hard time with it themselves. Let’s take a look at what “Endgame” teaches us about time and what it might mean for the future (and the past) of the MCU.


Early on in “Endgame,” the Avengers realize that they can use the Quantum Realm to travel to different points in their past. War Machine throws out the idea of just going back far enough and killing Thanos as an infant. Hulk immediately shoots down this theory, explaining that one cannot alter one’s own past because, to that individual, that past has already occurred.

The “Grandfather Paradox” is the term given to a classic time travel scenario wherein an individual travels back to the past and kills their own grandfather as a young man. That grandfather never has children and, as a consequence, the original individual is never born. But, because that man never had children, the time traveler never existed to go back in the first pace. If you were to do this in, say, the “Back to the Future” universe, you’d be in a awful lot of trouble. That film series suggests that such a paradox could rip reality apart. In the MCU, however, you can change the past. You just can’t change *your* past. That’s because of a branching multiverse.

Imagine if Tony Stark were to go back to the 1950s and, by accident or by intention, kill his father, Howard Stark. Instead of creating a paradox, the timeline would split and make a new reality where Tony was never born. If Tony were to return to his future through the quantum realm, he wouldn’t be going to the new reality. He would wind up exactly where he started with no changes whatsoever to his original timeline.


It is unclear exactly what the consequences are for creating new branches, but at least two additional timelines are created during the events “Endgame” (more on that in a moment). For the specific purposes of bringing together all six Infinity Stones, it doesn’t necessarily matter. If the Avengers were to simply pilfer the stones from the past and not return them to their respective eras, they could still theoretically use them in 2023 to bring everyone back from the snap. In doing so, however, they’d be dooming the branches they created.

As the Ancient One explains to Hulk, she cannot continue without the time stone. We know, for instance, that a few years after the Battle of New York, Dr. Strange will need the time stone to defeat Dormammu. If she gives it up to benefit another reality, her own reality is destined to fall to the Dark One.

Banner has a solution, though. By returning the time stone to 2012 after using it in 2023, he ensures that the structural integrity of the timeline remains through an act of predestination. Banner was always meant to borrow the stone and, presumably, even during her appearance in “Doctor Strange,” the Ancient One remembered having this encounter with Banner some years prior. That’s why the Avengers make the effort to put each of the time stones back exactly where they found them with, for the most past, no one being aware that they were ever borrowed.

Here's a map of the time travel that occurs in Marvel's Avengers: Endgame.


Despite their best efforts, the Avengers do allow at least two alternate realities to branch out of the events of “Endgame”. In 2012, following the Battle of New York, Loki winds up escaping with the Tesseract instead of being brought back to Asgard in chains. Then, in 2014, Thanos, Gamora and Nebula all travel to the future, never to return. Even if Steve Rogers managed to ultimately get the power stone back to Morag, a reality now exists without Thanos and Gamora. It’s possible that Star-Lord will encounters Rocket and Groot but without the Guardians of the Galaxy will never fully form and that branch will potentially see Ronan the Accuser come to power.

It is unclear whether or not it’s a problem that these branches still exist at the end of the film. One field of thought suggests that all realities exist and have always existed, but another might compare the multiverse to a sweater with loose threads. If they’re allowed to persist, there is the possibility they could lead to the collapse of the greater whole. Either way, it’s likely that these branches will be explored in future MCU stories, especially the upcoming Loki series on Disney+.

It’s also a distinct possibility that these branches could serve as a retroactive explanation for some of the more incongruous elements of the MCU. We have assumed that ABC‘s “Agents of S.H.I.E.L.D.”, for instance, overlaps with the main MCU timeline, but what if it has secretly taken place in this alternate Lokiverse branch the entire time? The same could potentially rewrite any of the Marvel Netflix series, relegating them to that 2012 branch or to the Guardians-less reality that launches from 2014.


Steve Rogers gets his happily ever after at the conclusion of “Endgame,” returning to the past to live out his days with the love of his life, Peggy Carter. Although we don’t know precisely the year that she and Steve reunited, we can assume that it’s sometime after the events of the “Agent Carter” television series. (In the comics, 1953 marked a brief resurgence of Captain America, later revealed to be a different person from the Cap who, during that era, was still frozen in ice). From what we know about the flow of time in the MCU, this means that a second Steve Rogers has always been around as Peggy’s unnamed husband. After all, if Steve instead branched off into a new reality by marrying her, he would not be around in the main MCU timeline at the end.

The secret life of Steve Rogers raises a lot of interesting questions and puts Steve up against some interesting moral issues. Has Nick Fury, for instance, known all along? Did Howard Stark? Could Cap have been in operation as a secret Avenger alongside Hank Pym and Janet Van Dyne? How difficult must it have been for Steve to know about future events and, for the good of the universe, be unable to do anything about it? Bucky is still out there being used as a remorseless killing machine for HYDRA. On the one hand, Steve sitting back and doing nothing feels antithetical to who he is. On another, though, it represents the ultimate character growth as, contrary to the events of “Civil War,” he’s forced to put his immediate principles aside for the greater good. It may even be that acquired perspective that finally lets him wield Mjolnir during that final battle.


While “Endgame,” in many ways, represents a culmination for the MCU, the future of the multitiered franchise also happens to look brighter than ever as record shattering box office results roll in and Disney+ teases a whole new format with which to expand. Given the prevalence of time travel stories in the Marvel comic book continuity, it’s probably a safe bet that, even after more than a decade we are only looking at a few threads in what is destined to become a vast narrative tapestry. Now that the rules seem to be firmly laid down, it’s up to future Marvel storytellers to discover creative ways to bend them. To that, there’s nothing more appropriate to say than, “Excelsior!

Silas Lesnick is the Senior Editor of Moviebill. He has been covering entertainment news out of Los Angeles for more than a decade. You can reach him via e-mail or on Twitter.