How Time Travel Worked in Avengers: Endgame

The following article contains heavy spoilers for Avengers: Endgame. Proceed with caution.

For years we have seen time travel work one way in film and television. Back to the Future, Terminator, 12 Monkeys, they all deal with time that moves in a straight line with any changes in time causing major disruptions. While, Avengers: Endgame approached time in a similar fashion, it also did something different, which left some fans scratching their heads.

If you understood the time travel mechanics in Endgame right away, then you are perhaps a time traveler yourself. If you didn’t, then this piece is for you. Personally, I love the use of time travel in cinema. I would go so far as to say that it is my favorite story telling device. It fascinates me, which is why I wanted to tackle this subject.

Time is a Tree, Not a River

So, time travel in Endgame. Let’s start with how Bruce Banner and Tony Stark explained it in the film. When Ant-Man said that it would be as easy as going back in time before Thanos got the gems, the science bros said “that’s not how time travel works.” Rhodes also proposed the “let’s kill Hitler” theory AKA let’s kill baby Thanos. Again, that’s not how time travel works, at least that’s not how it works in this film.

This does work in others films and shows, so it’s not a hard and fast rule, it just wouldn’t work for the story Marvel was telling, so they did something different. Instead of time flowing in one direction, like a river, they explained that time was more like a tree, with changes in the timeline creating new branches. You could call those branches alternative realities.

Within this theory, anything that the Avengers changed in the past would only create new branches in time. It would not change their own present or future, because their “future”, or anything that happened after they changed the timeline, technically already happened and could not be changed. So, if they couldn’t undo Thanos’ snap, what could they do?

Your Future is Your Past

They decided to take each gem out of their past, use the gems to bring everyone back, and then return the gems to the exact moment they took them. What would this accomplish? Every time they took a gem, a new branch in time was created. For instance, Loki took the tesseract in that new branch of time. Does that mean Loki is running out in the universe with the tesseract? No. Why not? Because at the end of the film, Cap returned the gems to the exact moment they were taken. That means they were never stolen and Loki never seized the tesseract from Tony.

Based on these mechanics, Cap never actually said Hail Hydra to Sitwell, Tony never hugged his father goodbye, and Nebula never killed her younger self. All those moments did happen for our current Avengers. They experienced those new branches in time, but for the people in the past whom they encountered, when Cap “trimmed those branches” by returning the stones, those timelines ceased to exist.

Fathers and Daughters

So, that solves the “does Loki have the tesseract” question. That also explains why they couldn’t undo Thanos’ snap. First of all, Tony didn’t want to undo the snap, because he would lose his daughter. So, what was his solution? Use the gems to bring everyone back to the current time, five years after the snap. This was the main crux of the movie and why time travel HAD to be different.

How is this different than Back to the Future? Technically Marty traveled back in time on accident and had to learn the rules as he went. In Endgame, the Avengers were intentionally going back. And there are similarities here because they had to be very delicate with the timeline so they didn’t lose little Morgan. This is similar to how Marty didn’t want to lose his family.

However, Endgame does differ from films like The Terminator and 12 Monkeys. Those films show how people who were sent back into the past actually created the future they were trying to change. John Conner is fathered by his best friend, a young Bruce Willis watches himself die at the airport, etc. Endgame didn’t loop back onto itself like this.

What About Thanos in 2023?

OK, so how about some more possible plot holes? What about Thanos? Thanos from 2014 transported himself to 2023. Then he died in 2023. Does that mean he would have never snapped his fingers in 2017 because he would have been absent from the original timeline? This is the question that has been keeping me up at night. And then I remembered the branch theory.

When Cap returned all the gems, he returned the Power Stone to Morag. This means that Thanos never showed up in 2023. His plan to acquire the gems still happened, he still gave up Gamora on Vormir, he still snapped 1/2 the universe away, and he lost his head to Thor’s axe in 2018. That’s how I understand cause and effect here. But, would that mean that no one really died in the finale battle of Endgame? Yes and no. Anyone Thanos killed would be alive. Tony wouldn’t though. Here’s why.

The Cost of Using the Stones

So, why did Tony still have to die? Because, as Lost so famously said, “whatever happened, happened.” Tony did not die by Thanos’ hand. He didn’t die because of a change in the timeline, which could be fixed or undone, he died by using the gems. Tony paid the price of the stones, as did Black Widow and Gamora. They can’t come back, even if the timeline was reset. Using the stones was like creating a fixed point in time. This is heavily explored in shows like Doctor Who, specifically the episode “The Angels Take Manhattan”.

So, the original timeline set out in Infinity War was restored, Thanos snapped, and everyone came back 5 years later when Hulk used the stones. Tony was lost, Black Widow was lost, and Gamora was possibly still lost. The effects of Thanos’ original snap were still undone, which meant Morgan and any other child born after the snap was still alive. This really was the only way to save Morgan AND everyone else.

And for the last possible plot hole: what about Mjolnir? Cap put Mjolnir back on Asgard when he gave the Aether back to Jane, so Thor always had his trusty hammer with him in that timeline. And Cap going back to be with Peggy? We never saw a photo of her husband, so it’s possible that they were married THE ENTIRE TIME. She did say “you came back” when she looked at Steve in Winter Soldier. Did she mean for the first time? Or back during her time?

If I missed anything, please let me know. You can reply to this article or you can tweet me directly at @LaurenGallaway on Twitter.

Avengers: Endgame is currently in theaters worldwide.