'Back to the Future' Fan Theories

Doc Brown may have actually used the time machine to save Marty's life on at least two definite occasions, according to Redditor /u/MECHEndal. The first occurs in BttF II when Marty jumps off Biff's building and Doc is, conveniently, there to save him. The same coincidence holds true later in the film when Biff chases Marty, who's riding the hoverboard - Doc arrives at the tunnel just in time with a string of flags to save him.

In both instances, Doc Brown seems to know exactly where to go to save Marty's life, which would be highly unlikely unless he had witnessed Marty perish before and was using the time machine to go back and save him.

Everyone likely remembers the scene where Biff tries to force himself on Lorraine before George stops him. One theory claims, however, that there may have been another event that directly contributed to Marty's originally dismal home life.

Redditor /u/mybustersword theorized that the depressed and alcohol-dependent Lorraine from the beginning of the movie suffered trauma from Biff's actions in her original past. The user pointed out that "when Marty allows George to stand up and protect Lorraine instead of doing so himself, Lorraine undergoes a miraculous personality change in the future." Not only does she get a happy marriage, but Biff is never able to violate her.

Redditor /u/amanwhodrinks may have stumbled upon the reason why Doc Brown decides to re-tape the letter Marty gives him in 1955. After Marty shares that he witnessed his father punching Biff outside of the dance - something George had never done previously - his picture with his siblings is still restored. Despite George doing something out of place, the space-time continuum is not disturbed.

This action may have given Doc the courage to read Marty's letter warning him about his impending end in 1985. The user further explained, "This makes more sense than having a major character keep such strong convictions for 95% of a movie and then in the last 10 minutes decides to do an about face for seemingly no reason."

Redditor /u/Ochobobo proposed that George isn't as clueless as many assume - he actually knows his son traveled to the past. Over time, George recognizes many of the actions, items, and inventions Marty mentions in 1955 as they come to fruition, such as Tab soda, the song "Johnny B. Goode," and both Star Wars and Star Trek.

In addition, Marty's prediction of George's 8-year-old son setting fire to the carpet would also indicate Marty's identity. As George was a sci-fi enthusiast, he may have been open to the notion of time travel.

By the end of BttF, Marty’s home life has completely altered for the better: His father's a successful writer and his mother has a much more optimistic personality. In addition, Biff is detailing cars and working for Marty's father, rather than the other way around.

Although Biff seems to get his just desserts, Redditor /u/SatNav pointed out that perhaps Biff's life takes a turn for the better. The theory claims that, after the events of 1955, Biff may have discovered a love for detailing after he cleaned his car following the manure accident. He may have discovered a skillset he excelled in, leading him to develop his business, Biff's Automotive Detailing.

One of the lingering questions from the original BttF film is how Marty's parents fail to recognize that their son grows up to look just like their mysterious high school friend. To answer this age-old query, Redditor /u/BPJordan38 proposed that George McFly - Marty's father - simply believes the Marty he met in the '50s was an alien.

George recognizes the fact that Marty begins pushing for him to ask Lorraine out at the same time he receives the mysterious visit from "Darth Vader from Planet Vulcan." Even the sci-fi book George later publishes adds substance to this theory. The Redditor explained:

I've become even more convinced of this because of George McFly's book. If you look closely at it near the end of the movie, it's called "A Match Made in Space." The cover features a boy who looks like George about to kiss a girl that looks like Lorraine being brought together by an alien wearing a suit. I've always thought that George McFly's book is just a re-telling of the whole film. George McFly wrote this book, which is to him a nonfiction account of what happened to him, but to the world is a science-fiction masterpiece by a little-known author.