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Schrödinger's Cap: 'Avengers: Endgame' and Quantum Superposition

WARNING: This article contains spoilers for “Avengers: Endgame”.

Last week, Moviebill took a spoiler-laden look at how time travel works in the Marvel Cinematic Universe, ultimately positing that, at the end of “Avengers: Endgame”, Chris Evans‘ Steve Rogers must have traveled back in time and secretly lived out his life with Hayley Atwell‘s Peggy Carter in the same “prime” MCU timeline in which all 22 films take place. Other fans were not so sure, arguing that Cap’s time travel would create an all new branch in reality. Then, just hours after our initial article was published, came confirmation that we were incorrect in our assumption… or did it?

“The time travel in this movie created an alternate reality,” announced director Anthony Russo during an interview with Chinese outlet QQ (translated via Reddit). “He lived a completely different life in that world. We don’t know how exactly his life turned out, but I’d like to believe he still helped many others when they were needed in that world.”

It’s hard to argue with one of the people responsible for ultimately realizing “Endgame” on the big screen. That is, unless you’re a different person responsible. Shortly after Anthony Russos’ comments were made, screenwriters Christopher Markus and Stephen McFeely, in conversation with Fandango, argued for precisely the opposite perspective.

“Steve going back and just being there would not create a new timeline,” said Markus. “So I reject the ‘Steve is in an alternate reality’ theory. I do believe that there is simply a period in world history from about ’48 to now where there are two Steve Rogers. And anyway, for a large chunk of that, one of them is frozen in ice. So it’s not like they’d be running into each other.”

There are certainly arguments to be made for both perspectives. If Captain America returned to the prime MCU timeline and lived a secret life with Peggy, it means that he would have had to make some harsh choices. With his knowledge of the future, Steve could have prevented global tragedies, ranging from real world events like 9/11 to MCU specific losses, such as the death of Howard and Maria Stark. How could Steve live a happy life with the knowledge that Bucky is out there functioning as a Hydra brainwashed killing machine? If we are to accept Steve’s time travel as predestination event within the existing timeline, we must accept that he had no choice and that he refrained from changing history in an effort to eventually get back to the same point in 2023 that he left.

It’s worth noting that Peggy Carter’s personal history is muddied as far back as 2014’s “Captain America: The Winter Soldier” (also scripted by Marcus and McFeely and directed by the Russos). In a 1953 filmed interview, Peggy refers to her unnamed husband as being a man that Captain America saved. Naturally, she wouldn’t be able to reveal that her husband is a time traveler, but there’s also a poetic angle at play if we interpret it as Captain America having ultimately saved Steve Rogers.

When 2014 Steve visits a dying Peggy in the hospital in “Winter Soldier,” her lines can also be read with a double meaning.

“I have lived a life,” she tells Steve as he looks at old framed photographs of Peggy and her children. “My only regret is that you didn’t get to live yours.”

Is she expressing sorrow that Steve didn’t get to live his life because he was frozen in ice, or is she hinting that he gave up his post-2023 existence for her? Could those two children secretly be Steve’s own?

Are these Peggy Carter and Steve Rogers' children?

Things are a lot more simple in the “alternate timeline” camp, but there are still some serious issues. Because we’re not privy to any of the details of that potential timeline, maybe Steve immediately rescued Bucky and began doing what he could to chart the best course possible for the future of America. There are, nonetheless, some serious moral questions that this raises. If Steve altered history to be with Peggy, he is effectively stealing the life of the mystery man that Peggy married in the timeline and, worse, erasing those two children from existence. There would also be another Steve Rogers still frozen in ice and, even if he is recovered and awakened early, it’s not exactly a happy ending for that version of Steve. The love of his life has already settled down with a man with whom he cannot compete: himself.

Although it’s not impossible to “No-Prize” together an answer, “Endgame” itself does not explain how the Steve from this potential split reality could then return to the prime timeline as an old man at the end. If it was always the same timeline, the answer is simple: he just lived through it.

“Avengers: Endgame” is far from the only film whose creators have different interpretations of the narrative. Star Harrison Ford and director Ridley Scott had diametrically opposed viewpoints on whether Ford’s Rick Deckard was a human or a replicant in 1982’s “Blade Runner”. On the audio commentary track for 1999’s “The Limey,” director Steven Soderbergh argues with screenwriter Lem Dobbs on crucial elements of the film’s plot, including whether or not the film is a sequel to Ken Loach’s 1967 drama “Poor Cow” (scenes of which were used as flashbacks in the latter film).

So who’s right? If we look at it through the lens of quantum theory, both viewpoints are simultaneously correct until proven otherwise. That’s because of a principle known as quantum superposition during which atomic and subatomic particles are said to exist in multiple states at the same time. That is, until those particles are measured and a single state is revealed.

In 1935, an Austrian physicist named Erwin Schrödinger devised a thought experiment to demonstrate the seemingly paradoxical nature of quantum superposition. In it, a hypothetical cat is placed inside a sealed box with a poison vial and a radioactive source. If the radioactive particles exist in an excited state, a Geiger counter reading will cause a hammer will strike to vial, releasing the poison and killing the cat. If the particles exist in a ground state, nothing will happen and the cat will be fine. If we are to accept that quantum superposition is causing those particles to exist in both states simultaneously, the cat is therefore both alive and dead at the same time. That is, until the moment we open the box and one of those potential realities collapses.

So until another film ultimately proves it to be one way or the other, let’s consider the fate of Steve Rogers in the MCU as “Schrödinger’s Cap”. Peggy and Steve lived happily ever after in the prime timeline and in an alternate reality, simultaneously existing in both states until one of those theories is collapsed in favor of the other. Of course, with the new “Spider-Man: Far From Home” trailer teasing the potential for a mighty Marvel multiverse, that collapse could happen sooner rather than later…


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.