The original Back to the Future is undoubtedly one of the greatest movies ever made - possibly even the greatest science-fiction movie as well. The writing is top notch, and unlike many other fantastical stories regarding time travel, it actually makes a lot of sense, is well-constructed, and doesn't leave behind a lot of lingering questions.
But it still leaves behind some lingering questions. As tightly plotted as the story is, it's certainly not perfect, and like all time travel movies, some of its inner logic doesn't really make a whole lot of sense. Of course, most of these "problems" are made in jest. The movie is still amazing.
Marty Looks A Lot Like Marty
One of the greatest questions concerning Back to the Future is the incredible similarities between "Calvin" and Marty. Did George and Lorraine never notice that their child looked a lot like Marty? That one guy they named their child after?
Of course, they only knew Marty for a week at best, so it's not like his face would be permanently engrained in their memories. But surely, they have some idea of his looks and voice, considering he played such a monumental role in their relationship and lives? Such an important person is not easily forgotten.
Dave Is Apparently A Better Name Than Marty
Another weird thing to consider is the naming of the McFly children. At the climax of Back to the Future, Marty reveals his true name to Lorraine, and she clearly takes a liking to it. The implication is that she named Marty after the Marty she met in 1955. But Marty isn't her first child - that's Marty's older brother, Dave. So why didn't Lorraine name her first son Marty if she liked the name so much?
It's not really a big deal, but it's still interesting to consider why she eventually came back to Marty rather than just using it the first time.
The Famous Grandfather Paradox
Okay, so Marty accidentally stops his parents from meeting and getting together. This results in Marty slowly disappearing from existence, as his parents never got together and Lorraine never gave birth to Marty. Fair enough. But what would have happened if Marty actually disappeared?
If he disappeared, that would mean he wouldn't exist in the present, which would mean he never accidentally prevented his parents from meeting, as he never traveled back in time... right? And for that matter...
The Conveniently Fading Family Photo
What exactly is the point of the fading? The fading photo is used to indicate the disappearing present, as George and Lorraine veer further and further from meeting each other and starting the McFly family. It isn't until George stops the guy from dancing with Lorraine that both the photo and Marty are fully restored to their original selves.
But the "fading" seems like little more than a plot contrivance meant to indicate "time is running out" for both Marty and the audience. There's literally no other reason for the photo (and Marty) to do that.
Marty Deliberately Cuts It Too Close
During the ending, Marty cuts it incredibly close making it back to Doc and the mall (famously now the Lone Pine Mall). But he has a literal time traveling machine and could have traveled back to any point in 1985.
He could have gone back a couple hours before the events at the mall took place, have a coffee, re-adjust to life in the '80s, and then go back to the mall with plenty of time to spare. But no, he decides to go back eleven minutes before Doc gets shot. Talk about playing with fire!
Doc's Bullet Proof Vest Is Too Strong
Speaking of the ending, it's very weird to consider that a mere bulletproof vest was the only safety precaution that Doc took to prevent his death. Doc is a smart person, and he is fully aware of his impending death, and yet he does the absolute bare minimum to protect himself. If he was shot in the head, he's... well... dead. Heck, if he was shot in a vital part of the leg he could have bled out in the parking lot.
And for that matter, there's no way that one Kevlar vest would protect Doc from those kinds of rounds and that kind of range. No matter how it's sliced, Doc should technically be a dead man.
Marty Is Too Cool For Alternate Timelines
At the end of the film, every member of the McFly family is depicted as being "cooler" than their pre-time travel selves. They seem more financially successful, they dress better, they have more ambition, they look healthier and more put together, and they're far happier as a family. Yet Marty is seemingly unchanged.
No one is curious as to a returning Marty's sudden change in behavior or even his rather plain clothes. By all accounts, "returning" Marty is exactly the same as his post-travel self. He must have been too cool for "more successful" alternate timelines.
Marty Orders A Pepsi Free In 1955
Back to the Future makes an easy joke when Marty arrives in the past by having him order both a Pepsi Free and a Tab Soda. But there's one small problem with this. Pepsi Free was introduced in 1982, only three short years before the events of the movie's present and decades after the movie's past.
Surely, Marty would have remembered its introduction and be fully aware that Pepsi Free doesn't exist in 1955. Of course, it's possible that this slipped his mind in the excitement of traveling back in time.
The McFly Family Is Too Trusting Of Biff
By all accounts, Biff is a horrible person. He legitimately tried killing Marty in the town square and even attempted to rape Lorraine at the school dance. So why on Earth are George and Lorraine keeping him around as the househelp?
Surely, Lorraine would be uncomfortable with keeping her attempted rapist not just in her life, but her home? Even if Biff doesn't gain access to time-travel, keeping him around seems like a recipe for disaster. It's obvious that Biff is totally subservient to George and his demands in the ideal future, but this still raises a lot of questions and red flags.
Darth Vader From The Planet Vulcan & Copyright Issues
In one of the most famous scenes, Marty appears to George in the middle of the night by pretending to be Darth Vader from the planet Vulcan. This disguise makes sense, as neither Star Trek nor Star Wars had been released yet, so George would really think this Vader is the real deal. But what happens when Star Wars and Star Trek finally do exist?
Surely, a few years later, George would have thought it awful weird and convenient that the "alien" who visited him shares the same names as a Star Wars villain and a planet in Star Trek. He also never forgot about the encounter or the alien's name and heritage, as the experience clearly influenced the novel he published in 1985 -- decades after the debuts of Star Wars and Star Trek. Did George get into a copyright battle with George Lucas and Gene Roddenberry? If so, who won? More importantly, how?!