Thanks to the series' place in pop culture and the nature of the franchise, Back to the Future trilogy theories have popped up across the internet for years. It's no wonder Back to the Future is often regarded as one of the best '80s movies. Fans have written a George McFly theory about his belief that Marty is an alien, a Lorraine Baines theory about her dark past with Biff, and countless others. Although casual viewers may be unaware of this vast underworld, many passionate Back to the Future fans regularly comb the pages of Reddit to find the best Biff Tannen theory or dark Doc Brown theory.
Some of the most innovative notions use elements that occurred behind the scenes of the films, ultimately claiming them as canon. For example, one Marty McFly theory hypothesizes that actor Eric Stoltz - Marty's original actor who was ultimately replaced by Michael J. Fox - actually existed in the Back to the Future timeline. On a rainy day, try rewatching the Back to the Future films and see if the following fan theories hold water. And if you're a real BTF fan, beware of this list of Back to the Future plot holes that might ruin the whole series for you.
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.