I’m sure many of you have seen “Avengers: Endgame.”
For those who have yet to see it, spoiler alert: This article will discuss whether time travel — a major plot device in the movie — checks out from the scientific perspective. You’ve been warned.
Time travel is the backbone of “Endgame,” which follows the aftermath of “Avengers: Infinity War.” Five years earlier, Mad Titan Thanos used Infinity Stones — reality-altering stone-like objects embedded in his gauntlet — to erase half of all life in the universe, including a lot of members of the Avengers team. Bringing them back to life would require the remaining Avengers to travel back in time, gather the Infinity Stones, assemble a gauntlet of their own, and undo what Thanos did.
However, time travel is tricky.
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Split reality
Contrary to what the movies “Back to the Future” or “Terminator” proposed, traveling back in time to kill baby Thanos wouldn’t solve the problem; people he erased from existence would remain dead. That is because “Avengers: Endgame” adheres to the Many Worlds Theory (MWT).
This theory argues that once an action — any action — is performed, the universe splits itself into two versions: One where an action was not carried out, and another where it was. Killing baby Thanos would therefore result in a split reality where he wasn’t born to carry out his plan. However, nothing would have changed for the Avengers, since they would remain in their own reality.
Using this set of rules, the movie enables many happy (and some not-so-happy) past-present reunions, including Thor meeting his mother in the past, Iron Man spending quality time with his father, and Captain America fighting … himself. MWT is a useful plot device, because it does away with the Grandfather Paradox. (The paradox states that if you go back in time and kill your own grandfather, you would cease to exist, thus making your grandfather’s death impossible.)
This line of reasoning plays a crucial part in Deutsch proposition, a theory formulated by British scientist David Deutsch and mentioned by Iron Man in “Endgame.”
However, there’s one important topic we haven’t discussed yet: How do you travel back in time in the first place?
In “Avengers: Endgame,” heroes shrank themselves to a sub-atomic size, entered the Quantum Realm (“a place where time and space are irrelevant”), and navigated it using special suits and devices (“time-and-space GPS”) in order to emerge in different places and time periods. The goal was to take hold of the Infinity Stones before Thanos could seize them.
Enter Einstein
While visiting Quantum Realm in the strict comic book lore interpretation is just “movie magic,” the portal connecting the past and the present could actually be a wormhole — also known as the Einstein-Rosen Bridge. A wormhole can be visualized as a tunnel with two ends, each at a separate point in spacetime (i.e., different locations or different points in time).
While still being a theoretical concept, wormholes are consistent with the general theory of relativity, and this is where the “Endgame” time travel plot gets closest to the real science. Using wormholes, superheroes can traverse both space and time, get Infinity Stones and then return to their point of origin. And that is precisely what they did in the movie.
Although “Endgame” broke its own rules of time travel a few times in favor of the dramatic effect, it’s still refreshing to see a superhero flick that tries to base its plot on relevant scientific theories instead of explaining everything with magic and superpowers. For me, this made the movie much more enjoyable and even educational!
What’s your take on time travel? Do you think it’s possible? Let me know in the comment section below.
Jurica Dujmovic covers technology for MarketWatch.
