After all of this time travel, the 1985 film Back to the Future sounded like a good conclusion; however, behind its positive implication, Marty's family appears to have improved substantially; his father is no longer bullied, and his siblings are happier and better adjusted. The film's premise sees Doc (Christopher Lloyd) take Marty (Michael J. Fox) to the past where he accidentally disrupts his parents' chance meeting and threatens his existence. He then spends his time
Since Marty was stuck in the past, it slowly becomes apparent that another version of the character had been born into the new timeline that allowed for a happier and more comfortable version of his family. This alternate version of Marty would have different memories and ultimately a different existence than the one he had before leaving for the past.
Doc takes Marty away to do another time travel adventure shortly after, allowing the audience and Marty to ask questions about the present situation.
A Version of Marty was erased by Back to the Future.
Marty returns to 1985 a few minutes earlier so he can rescue Doc from being shot down by Libyan terrorists. Before escaping in the DeLorean, Marty sees another Marty from the same perspective as the beginning when Marty teleported to the past. Does that mean that Back to the Future closed the loop with that end?
It is safe to assume that the second Marty was completely erased from existence since that version of Marty never returned and the original Marty continues to live his life. This is quite horrifying as the Marty we follow through the franchise is essentially an imposter from another timeline who has taken their son's place.
Doc Brown might have saved the McFlys from knowing the truth.
Doc's insistence on Marty leaving with him at the end of Back to the Future implies that he knows something wrong with the well-off Marty. This suggests that if Marty were to remain, he might tell his parents about the time travel adventures, which might lead to Marty's being erased as discussed above.
It is difficult to look back at the ending of Back to the Future without acknowledging the secretly horrifying fact that Marty is an alien to a new timeline, and that the version of Marty that belonged to that era had been erased and forgotten. This dark ending hidden behind a happy conclusion demonstrates how fascinating, unknown, and unpredictable time travel is in the science world.
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