“He would have realised that the flux capacitor would send itself through time but not through space so the only form of travel would be limited to whatever held the device itself. To begin his experiments, it would then be logical to stay within the area of Hill Valley.
“This would allow him to easily return to his ‘safe harbour’ of 1985 and measure if anything he did in the past had altered the future. No matter how much he would try to avoid disrupting the timeline, the butterfly effect would still be in place though there is no way to know for sure exactly how much of an effect that this could have on the timeline.”
But once Doc had his home base of 1985, the fan believes the inventor needed someone close by with a family history in Hill Valley from the very beginning; someone who he could monitor and note the changes in the timeline after he time travelled.
READ MORE: Back to the Future theory: Marty’s 1955 actions improved Biff’s life
The theorist argued: “Throughout history, his family also had a pattern of being bullies with an entourage.
“This means that they have always been too well known; if a small change happened in the Tannen timeline, it could have large, rippling effects on history.
“Looking at the Tannen family in the 1980s, there was only one Tannen that was an option – a middle-aged, alcoholic bully. This threw out that option.”
They continued: “Around since the beginning of Hill Valley, this family seemingly has no large contribution to its history – mediocre from beginning to the present. Small variances to this family’s history would cause no large, sweeping changes to the timeline.
“Looking at the family in the 1980s, you have an average American family not making any ripples. The older brother works at a fast food restaurant, the sister seems vain, one parent a pushover and the other an alcoholic, then there is the youngest son – a boy with ambition who dreams big and is only held back by the family in which he was raised.
“He dreams big, has an open mind, and is more intelligent than he lets on. This is the perfect person for Doc to keep as his ‘constant’ in 1985.”
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“The McFlys were always around and would be influenced by the town but never did any influencing of their own. If there is a change in Marty, Doc can trace back the McFly timeline and see what he accidentally did to affect the timeline.”
Of course, they also pointed out that Doc didn’t expect to be shot dead by terrorists when attempting to time travel for the first time.
As a result, Marty went back to 1955 by accident and then saved his life by writing that warning letter and giving it to younger Doc.
By the time we get to Back to the Future Part III, 1955 Doc has met two Marty McFlys and sent the latest version of “future boy” back to 1885 to stop 1985 Doc being killed by Mad Dog Tannen.
The 1955 Doc in this final timeline would grow up knowing everything and so would purposely seek out a friendship with Marty; not to monitor the timeline but purely to maintain it based on the casual loop or bootstrap paradox that he has experienced.
READ THE FULL REDDIT FAN THEORY HERE