Although Back to the Future’s ending should technically feature at least two different versions of Marty McFly, there are a few explanations for how the sci-fi comedy sidestepped this obvious logical problem. The Back to the Future movies don’t run on pristine logic. Back to the Future’s depiction of lightning might be surprisingly accurate, as a strike does provide the amount of energy that Doc Brown claimed the DeLorean needed. However, there are plenty of infamous plot holes that prove the trilogy’s depiction of time travel relies on viewers ignoring a lot of missing explanations.

Take, for example, the way that the almanac changes in Back to the Future Part II. Every time Biff bets on a sporting event, his win should change the outcome of the next event, and so on. However, this never becomes an issue thanks to the ripple effect ensuring that the sports almanac’s contents change to reflect this new reality. This seems fine until viewers ask why the publisher published the same almanac in every version of his reality, how Marty happened to find it in every version of this reality, and how Biff stole it in each one.

There Should Be Two Versions Of Marty McFly At The End Of Back To The Future

Back to the Future Ignores The New 1985’s Resident Version Of Marty

This is just one of many times that the trilogy’s logic doesn’t quite add up. For every well-researched moment in the trilogy, like Back to the Future Part III’s surprisingly accurate “Dude,” there are plenty of plot holes like this. Perhaps one of the most infamous is the question of what happened to the original version of Marty in the original movie’s ending. When Marty returns to the new, improved 1985, he replaces himself in his now-happy life where his family is now rich and successful.

The problem is that the original movie never explains what happened to the version of Marty that already lived in the ending’s perfect reality. In Back to the Future‘s ending, this version of Mart is preparing to travel through time just as the main Marty arrives back in Hill Valley, but the movie never tells viewers what becomes of him. Not only that, but this version of Marty will eventually return from 1955 and another, third version of him will leave for 1955, meaning viewers are left with an unending string of Martys all traveling to 1955 and altering their futures.

Did The Second Marty McFly Travel Back In Time Just Before Our Marty Came Back?

Marty McFly May Have Time Travelled To Avoid This Paradox

Theoretically, the version of Marty who lives in the happy timeline is leaving for 1955 when Marty sees him in Back to the Future’s ending. However, it is important to note that Marty’s life is already perfect in this version of reality. As such, he doesn’t need to change the past again, meaning there is now no reason for this version of Marty to travel back in time. If anything, he is likely to unintentionally make things worse.

This is what happens later in the trilogy when Doc Brown’s Back to the Future Part III story sees him accidentally get himself killed when traveling back to the Wild West. This event is undone before the trilogy wraps up, but it still draws attention to the biggest problem with this plot. To avoid destroying the perfect life that he created by traveling to 1955, Marty would need to stop his alternate self from changing the timeline again. This could cause further issues, leading to the question of whether the second Marty must stop the third version of himself and so on ad nauseam.

If The Second Marty Went To 1955 Too, He Must Have Changed The Timeline Again

Marty Time Traveling Again Would Further Alter The Timeline

Inevitably, the second version of Marty wouldn’t be able to change the timeline in the same way as his predecessor, meaning he would likely make things worse for Marty in the present 1985. After all, all of Marty’s problems were solved when he returned to 1985. Any further changes risk jeopardizing this and don’t necessarily come with extra benefits.

As such, it seems reasonable to suggest that Marty needs to close this loop as soon as possible. The problem is that this would mean killing an alternate version of himself, which is exactly what one Back to the Future fan theory proposes. This might be the canonical solution, but there is another, less bleak explanation of the character’s fate.

Back To The Future’s “One Timeline” Rule Creates An Infinite Marty McFly Problem

Marty Eventually Must Replace Himself For The Franchise’s Timeline To Work

The main reason that every version of Marty can’t exist simultaneously is the franchise’s vague “One timeline” rule. Put simply, Doc Brown informs Marty that no amount of changing the timeline can alter things too drastically, and the one true reality will always eventually reinstate itself one way or another. Viewers can see this theory in effect throughout the series in both minor and major ways, as history seems to repeat itself over a hundred years in Hill Valley.

The same family that owns a horse dealership in the Wild West own a car dealership in 1955, 1985, and 2015. This proves some things never change, judging by this Back to the Future trilogy Easter egg. There are plenty of similar hints that Marty can’t alter reality too drastically no matter what he does throughout the series, since the main timeline will always eventually reᴀssert itself. However, if viewers ᴀssume that Doc was wrong about this hypothesis, there could be an infinite number of realities coexisting simultaneously. Then, the Martys could all exist without destroying each other.

There Is An Easy, Dark Solution To Back To The Future’s Marty McFly Problem

Doc Brown Could Have Killed The Second Marty

Even though this seemingly disproves Doc Brown’s expertise, it remains the most likely explanation for what happened to the other Marty in Back to the Future’s ending. After all, the alternative explanation is that Doc Brown intentionally programmed the DeLorean to ensure that version of Marty would die, meaning the loop would no longer continue. This makes logical sense, but would be a profound betrayal of the pair’s relationship.

Some viewers might be able to stomach the idea of Doc killing off an alternate version of Marty out of necessity, but it seems much easier to imagine that his understanding of the timeline was off. While Back to the Future‘s DeLorean plays a big role in shaping the reality of the series, it is hard to see Doc using it to kill off his research ᴀssistant and friend to avoid a temporal paradox. As such, viewers could take the absence of Marty’s second self in Back to the Future’s ending as evidence that the multiverse is real.