You know, there’s a serious issue with going back in time. Once you’ve gone to the past, you can never return.
Take the movie ‘Back to the Future’, for instance. At the end of the movie, Marty McFly did not return home. He went to an alternate 1985 where his dad was more successful, Doc Brown hadn’t died, and Biff Tannen had become his father’s lackey. This is not the timeline he left.
As soon as he traveled to the past, Marty changed the course of history. In doing so, one of two things occurred. Either his original timeline ceased to exist, or the timelines split from the moment he reached the past – stranding him from his original chronology. Either way, he could never return to his own 1985. This could have potentially serious consequences.
You see, when Marty entered the DeLorean and traveled to the past, he forfeited his place in history. His interference led to a few important changes. His parents met under slightly different circumstances. They still got married and had a child named Martin, but this child was not Marty. This new Martin grew up and had a life that was not quite the same as original Marty’s.
When Marty traveled ‘back’ to the future and found a new timeline in place, he was a stranger. The new Martin that resulted from his interference was the native. Luckily for Marty, Martin had himself just traveled to the past, never to be seen again. This spared Marty the awkward confrontation with his doppelganger.
But had this confrontation taken place, it would have gone like this…
Marty returns to what he believes to be his home and heads for his room. Exhausted from his adventures in time, he plans to head straight for his bed and take a nap. Upon entering his room, however, he finds someone already in his bed. This someone is Martin – a slightly more spoiled and lazier version of himself. Martin is stunned to see himself walk through the door but Marty pieces it together very quickly. He realizes that he has trespassed in this timeline and that someone is already occupying his place in the world. This is unacceptable. Martin has to go.
Marty capitalizes on Martin’s slow and confused reaction. The struggle is brief but brutal. When it is over, only Marty remains. But what to do with the body? The solution is simple and foolproof. With the DeLorean in the garage and away from prying eyes, he safely loads the body into the car. He drives the DeLorean out to a secluded spot, sets the time circuits, and drops a cinderblock onto the accelerator. He watches the DeLorean, along with the evidence, vanish into oblivion.
Marty briefly wonders what will happen when someone in the past discovers a time machine with a dead body in it, but he quickly puts it out of his mind. The DeLorean and the body are in their own timeline now. They can never come back… to the future.