Plot synopsis
Marty, now trapped in 1955, receives a letter from Doc Brown written in 1885 from the Wild West with instructions on how to find the time machine. He succeeds and goes back to 1885 where he saves the Doc’s life.
Marty is careful not to do anything that will alter the course of events through time because when he goes back to 1985, he does not want the timeline to have changed.
When they are ready to return, they realise that the DeLorean time machine has run out of petrol. So, they use a stolen steam train to push it to the required speed. At the last minute, Doc decides to stay, but Marty gets in the car and returns to 1985.
Just after he gets out of the car, an oncoming cargo train completely destroys it, which puts an end the time-travelling adventure once and for all!
My comments
This movie returns to the premise used in the first movie, where one has to be careful not to change too much, or the timeline will diverge forever. This of course could cause the grandfather paradox and prevent Marty from being born. However, I am not sure how Doc staying in the past and marrying will not have consequences in the future.
This brings us to another issue: How much do you have to change the past to make a significant difference in the future? The review of Déjà Vu (2006) discusses this aspect of the double-well model of time more fully.
Summary of time travel
The double-well timeline is used again in this final film of the trilogy. Marty and Doc do not do anything significant enough to cause the timeline to diverge so far that it cannot converge back to the original. Therefore, Marty is able to return to the same 1985 that he left.
The timeline is the same for the both of them, as they start in 1955 and travel to 1885. The only difference is that at the end, Marty travels to 1985 while Doc stays in 1885.
Category of time travel
Science fiction: a time-travel vehicle.
Model of time
Open past, open future with a double-well timeline.
Guyline for Doc:
Guyline for Marty:
