Avengers: Endgame brought time travel into the mix as many suspected it would as the remaining heroes made their best effort to undo the effects of Thanos snapping his fingers and wiping out half of the universe. In doing so, the film introduced a time travel theory like none seen before it in movies or television. Now, co-director Joe Russo has gone on record to explain the Marvel Cinematic Universe's time travel rules.
Spoilers for Avengers: Endgame follow. Major spoilers!
In two sequences, both of which involved Bruce Banner, Avengers: Endgame attempted to explain how their time travel rules worked. Still, fans left theaters with questions about the mythology of time travel as it applies to the Avengers' world, given some characters died in the past or changed their own storyline as fans knew it.
"It's not a time loop," according to Joe Russo in a recent Q&A. "Both Ancient One and Hulk were right. You can't change the future by simply going back to past. But it's possible to create a different alternate future. It's not butterfly effect. Every decision you made in the past could potentially create a new timeline. For example, the old Cap at the end movie, he lived his married life in a different universe from the main one. He had to make another jump back to the main universe at the end to give the shield to Sam."
The closest comparison to the rules of time travel seen in Avengers: Endgame are those of the popular TV series LOST but with extra conditions added on to it.
In LOST, the rules were that you simply could not change the past. Visiting a previous point in time simply meant it was the character's present but it had already happened for everyone else in your timeline despite said character experiencing it for the first time.
In Endgame, the Ancient One made a strong suggestion against changing the past, meaning that the characters who changed anything would also have to return everything to how they found it. Regardless, nothing would change the characters' present scenarios. If changes were made, a new timeline would splinter off of the one which they had experienced, but the original would also remain intact.
This means there may be multiple new timelines spawning from Avengers: Endgame, including one where Nebula and Thanos disappeared from 2014, having died. Meanwhile, Gamora from that same timeline is also gone and living in the present. Also, Loki disappearing from New York with the Tesseract spawns its own new timeline, as well. This would mean there are at least two new timelines splintering off of the timeline which Marvel Cinematic Universe fans came to know since 2008. This does not include the timeline where Steve Rogers lives in the past with Peggy Carter, ultimately ending up in the same reality as the Avengers he left behind after defeating Thanos.
Whether or not these timelines will be introduced or explored in future films is unknown. However, Tom Hiddleston is set to play Loki in a Disney+ streaming service centered around the character, making a launch point from his disappearance from 2012's New York a perfect start.
Do you have questions or theories about the time travel rules in Avengers: Endgame? Leave them in the comment section or send them to me on Twitter and Intagram! Also, tune into ComicBook.com's Game Over: An Evening With Joe Russo on May 6 for a chance to get more of your questions answered!
Avengers: Endgame is now playing in theaters.