Doc Brown looking confused

It’s little wonder that the "Back to the Future" trilogy is one of the most popular film series in the history of Hollywood. Packed with brilliant characters, funny dialogue, and a whimsical yet compelling story, there’s everything you need across the three movies to keep fans of all ages entertained. Watching Marty McFly travel back in time thanks to Emmett "Doc" Brown’s DeLorean time machine and interact with his parents while trying to fix the timeline simply never grows old.

Yet, when it comes to time travel movies, there’s always some confusion. After all, the complexities of traveling through time and the method by which it actually works are sure to cause some problems and paradoxes. "Back to the Future" is no exception, and while the time travel is pretty simple in theory, it does pose a variety of issues if you look closely enough, and the way characters like Marty and Doc interact with their future and past selves only compounds the confusion.

So it should come as no surprise that fans have some pretty difficult questions about the "Back to the Future" films. Fortunately, most of them can be answered using information from the movies and the filmmakers themselves. If you’ve ever had a burning question about "Back to the Future," the answer you need might be right here.

Why don’t Marty’s parents recognize him?

Marty McFly with his parents

For the majority of "Back to the Future," Marty is stuck in the year 1955 after escaping from Libyan terrorists in the DeLorean. It is here that he encounters his parents in their teenage years. Both his father, George, and his mother, Lorraine, are 17-year-olds about to attend the Enchantment Under the Sea dance. However, the pair are not romantically involved when Marty arrives, and his intervention almost puts a stop to them becoming a couple.

Obviously this development threatens Marty’s very existence, but he’s able to put a plan into action that ends up with him helping George become a more confident person who is able to win the affection of Lorraine. The only problem is that by this time, Marty has spent a decent amount of time with his parents in the guise of "Calvin Klein." This poses the question of why his parents don’t recognize Marty as Calvin in 1985, when they look exactly alike.

This question has been answered directly by Bob Gale, one of the two screenwriters of the original film. Speaking to The Hollywood Reporter, Gale explained that the adult George and Lorraine likely only have a faint memory of Calvin, as those events occurred 30 years prior and they only saw him for a few days. Gale suggests that anyone would struggle to remember exactly what a person looked like under such circumstances without a photograph for reference.

Where did old Biff go?

Old Biff scowls

Much of "Back to the Future Part II" sees Marty and Doc attempting to undo the damage done by Biff traveling back in time to give his younger self the sports almanac so he can make a lot of money. The antagonist is able to steal the DeLorean and travel to 1955, then return to 2015, where he mysteriously disappears and is never seen again. This has led to fans questioning exactly where this older Biff went and what happened to him.

Screenwriters Bob Gale and Robert Zemeckis, who also produced and directed the film, respectively, apparently intended for viewers to see old Biff being erased from the timeline in much the same way that Marty was beginning to be in the original movie. In a scene that was ultimately cut from the final edit, old Biff can be seen stumbling from the DeLorean clutching his chest as he disappears — the exact same symptoms Marty suffered from.

In this case, because Biff had likely died much earlier than 2015 (possibly after being shot by Lorraine), the process of Biff being removed from the timeline was far quicker and more violent than it was for Marty. The filmmakers also suggested that, since the sequence didn’t make it into the movie, other interpretations could involve something like old Biff suffering a heart attack from the sheer shock of his time travel escapades.

What happened to the Libyans?

A Libyan brandishes a gun

Although they’re far from the most important characters in the trilogy, the Libyans who appear at the beginning of "Back to the Future" play an integral part in everything that happens afterward. Doc sourced the plutonium for his DeLorean time machine from a group of Libyan terrorists, who stole it from a nuclear plant. The agreement was supposed to see the scientist build a bomb for them, seemingly so they could use it in some sort of attack. However, Doc misled the terrorists, prompting them to try and get revenge by gunning him down.

The last viewers see of the Libyans is when they’re chasing Marty through the parking lot, and they aren’t mentioned at all when he returns to 1985. This has led to questions about where they ended up. The novelization based on the movie by author George Gipe has some answers about what may have happened, however. According to the book, the Libyans crash their van when Marty goes into the past and are trapped in the vehicle while police sirens can be heard in the background. This suggests that they’re captured by law enforcement almost immediately and thrown in jail.

Why didn’t Doc create gasoline in 1885?

Doc and Marty in cowboy costumes

A major plot point in "Back to the Future Part III" is that Marty becomes trapped in 1885 after he travels back to save Doc from being shot and killed by Buford Tannen — the DeLorean doesn’t have enough gasoline to drive because its fuel line was damaged when Marty first arrived. This means it can’t reach the 88 miles per hour it needs to time travel, despite modifications that make the use of plutonium unnecessary.

Many fans wonder, however, why Doc can’t just make some gasoline himself. After all, a scientist capable of developing time travel would surely not have any issue with creating gasoline or a similar substance to power the car, and it would make the whole plan to push the DeLorean with a steam train unnecessary.

That’s actually not the case, though, at least according to Screen Rant. Doc’s speciality is physics, not chemistry, so he might not have the expertise required to create gasoline — or at least, not the quality of gasoline needed to get a modern car up to speed. Meanwhile, the DeLorean hidden in the cave for Marty to find in the future would also not be a viable option, as Doc would have either drained the car of fuel before storing it to stop the gasoline going bad or prevented Marty from using it because of possible time travel paradoxes and potential damage to the space-time continuum.

How did George originally get together with Lorraine?

George and Lorraine kissing at the dance.

Near the end of "Back to the Future," Marty is attacked by Biff and locked in the trunk of the band’s car. Biff proceeds to try and forcefully kiss Lorraine — until George comes to the rescue and punches the bully, knocking him unconscious and saving Lorraine from further harm. The pair then go to the dance to share their first kiss and fall in love, as they were originally meant to. Only one thing stands in their way — a previously unseen student who comes along and forces Lorraine to dance with him, instead, until the newly confident George stands up to him and pushes him away.

The only reason George is able to make a stand like this is because he was given the confidence to do so by interacting with Marty throughout the week. And yet, in the original timeline, he still ends up with Lorraine, which begs the question: How did he manage to push the jerk away without Marty’s intervention?

This is actually an easy question to answer. The only reason this other student comes over to dance with Lorraine in that particular moment is because Marty delayed the evening’s events, first by taking Lorraine to the dance in George’s place, then by getting locked in the truck, delaying the band’s performance. If he hadn’t traveled back in time, George and Lorraine would have started dancing much earlier and would have kissed long before the jerk arrived.

How does the DeLorean time travel when struck by lightning?

The DeLorean being struck by lightning.

When Doc designed the DeLorean, he required it to reach 88 miles per hour before it could activate the flux capacitor, which is the core time travel mechanic of the "Back to the Future" series. However, the DeLorean travels to 1885 at the end of "Back to the Future Part II" after getting struck by lightning in a seemingly stationary position. That shouldn’t be possible according to the rules established in the franchise.

The solution is partially explained in the letter that Doc sends Marty from 1885 at the end of "Back to the Future Part II" — the lightning strike overloaded the time circuits in the DeLorean and activated the flux capacitor. Bob Gale and Robert Zemeckis later stated that the strike forced the car into a rapid spin, causing it to reach a speed of 88 mph while rotating. This is also the reason there appear to be flaming spirals in the air in the wake of the strike — the DeLorean leaves a trail of fire when time traveling, and the spirals are clear evidence of the spin.

Where does Marty get the hairdryer?

Marty McFly as Darth Vader

During one of Marty’s first encounters with his teenage father in 1955, he dresses up as an alien being known as Darth Vader in a misguided attempt to use George’s love of science fiction to influence him into pursuing Lorraine. Dressed in what appears to be protective clothing, Marty blasts Van Halen music at George and has a modern hair dryer tucked into his belt. But lightweight handheld hair dryers like this one wouldn’t be widely available until years later, so how did Marty get his hands on the device?

According to Bob Gale and Robert Zemeckis, Doc packed the hair dryer in a suitcase that was tucked away in the trunk of the DeLorean. So when Marty arrived in 1955, he simply had to search the car to find the suitcase with the hair dryer inside. Because it was such an unusual item for the time, it made sense to use it to scare George and help convince him that he was an alien being. A scene showing the hair dryer being discovered by the past version of Doc in 1955 was filmed but cut from the final version of the movie.

What happened to Biff’s son?

Griff and his gang

Biff Tannen is one of the main characters in the "Back to The Future" series and plays a central role throughout the franchise. Viewers get a chance to see Biff in the main 1985 timeline as a contemporary of George and Lorraine, as well as his teenage self from 1955. "Back to the Future Part II," meanwhile, introduces the audience to Griff, Biff’s grandson, who is a teenager in 2015 and leader of a gang of juveniles. But while "Back to the Future Part III" gives us a glimpse at Biff’s ancestor, Buford "Mad Dog" Tannen, some fans have questioned why we never get to see Biff’s son.

On the official "Back to the Future" site, Bob Gale and Robert Zemeckis suggested that it’s entirely possible Biff doesn’t have a son. While both Biff and Buford share the name Tannen, Griff’s surname is never actually established, so it’s unknown whether he is actually named Tannen. This makes it entirely possible that Biff had a daughter who then gave birth to Griff at some point in the future.

Why does Jennifer faint when she sees herself?

Old and young Jennifer meeting each other

In "Back to the Future Part II," Marty, Doc, and Marty’s girlfriend, Jennifer Parker, travel to 2015. Once there, Doc knocks Jennifer unconscious using a futuristic device to stop her learning too much about the future before he and Marty go off to try and help the couple’s children. While she’s asleep and abandoned in a back alley, police discover Jennifer and identify her before giving her a lift to her future home, where she encounters her future self. Both characters faint almost immediately — but it’s never explained why.

Doc is aware of the problems with Jennifer running into her future self, telling Marty that it could threaten the entire fabric of the universe if the two meet. While this doesn’t happen, it still seems strange that the Jennifers faint, especially when other characters have met their future or past selves with little consequence. According to the filmmakers, the reason Jennifer faints is simply because of shock — the older Jennifer obviously recognizes her younger self, and the younger Jennifer knows she’s meeting her future self and was not prepared for the sight of herself as an older woman. In contrast, when old Biff interacts with his younger self, the teenage version doesn’t recognize him and understandably isn’t shocked into unconsciousness by the sight of what is, to him, a random old man.

Why doesn’t Doc remember everything that has happened to him in the past?

Doc in his lab

There are multiple instances throughout the three "Back to the Future" films in which Doc learns about future or past events, and yet he often doesn’t seem to remember that these things happened. For example, Doc seemingly forgets that back in 1955, he suggested Marty wear a cowboy outfit when traveling back to the Old West. Similarly, the Doc from 1985 should be aware that Buford Tannen is going to shoot him while he’s stranded in the past, since the 1955 version of Doc learns this information via Marty.

Bob Gale and Robert Zemeckis have offered several explanations for why Doc doesn’t seem to remember this type of information. The first is that time travel doesn’t actually affect human memory, so knowledge like that listed above doesn’t ripple throughout the timeline. The second is that Doc has suffered from some kind of memory loss between 1955 and 1985, possibly as a result of an accident or experiment (or, as the filmmakers suggest, drug use in the 1960s).

The third explanation is that Doc does remember the information, but chooses to ignore it, taking care to do the things he originally did so as to not cause any paradoxes. Finally, Gale and Zemeckis point out that the space-time continuum might naturally erase important information like this in order to protect itself and stop paradoxes from happening on its own.

How does Marty know about the stopped clock if it was never broken by lightning?

The stopped clock in Back to the Future

The finale of "Back to the Future" sees Marty and Doc take advantage of a lightning strike to power the DeLorean and allow Marty to make it back to 1985. The pair know exactly when the lightning will strike thanks to the fact that the strike broke the clock, stopping its hands at 10:04 pm. Marty becomes aware of this in 1985, when a charity worker hands him a pamphlet about preserving the courtroom clock as a piece of the town’s history.

To get the energy from the lightning to the DeLorean, Doc fixes cables from the top of the clock down to the road. This presumably means the electricity bypasses the clock, which in turn means it never gets stuck at that time. This creates a paradox — how would Marty know when the lightning strike would be in 1985 if the clock was never actually struck and its hands never stopped?

There are two possible answers to this question, both of which essentially argue that the clock still gets broken, even with Marty and Doc altering events. First, the cables are wrapped around the clock’s hands, so the lightning strike could possibly have still damaged it. Second, Doc may have taken it upon himself to deliberately ensure the clock was stopped at 10:04 to stop any potential paradox, well aware of the danger such a thing could cause.