Originally Posted by sn939
Marty starts to fade out because the probability of his very EXISTENCE is coming precariously close to 0 when George and Lorraine almost don't kiss. Its really that simple...
The argument you're making for Doc is far more convoluted...
Okay, let us assume the age-related argument for Doc is true. Now imagine this scenario-
Original Marty is at least a little over two weeks older than FCB Marty, because of all the time travel he's done in the movies and the game so far.
Now let us assume that at some point while he's in FCB 1986, Marty decides to kill off his alternate counterpart. So he hires an assassin and gives that assassin PRECISE instructions to kill his alternate self exactly ONE WEEK later! The assassin has a 100 percent success rate and essentially, there is absolutely NO CHANCE in hell that FCB Marty can avoid getting killed. His fate is sealed. The most likely future is one where FCB Marty is DEAD a week from now.
Now, by your logic, the moment Original Marty gives the assassin the instructions which seal his alternate counterparts fate beyond a shadow of a doubt...he should fade from existence! Why? Because if FCB Marty is X years old, and Original Marty is X+2 years old...then Original Marty cannot possibly exist any longer because the timeline KNOWS that FCB Marty is not going to live beyond X+1 years...never mind the fact that the killing is scheduled for a WEEK later!
You can see now how illogical and convoluted this argument is...
Well there is no proof an alternate marty still exists. In fact there's proof it doesn't work this way; the eastwood timeline is an alternate timeline for marty (who is from twin pine). He's been there for 6 months and there's clearly no eastwood Marty lurking around.
There is proof the timeline can predict the future without time travel; in part II when Marty burns the almanac, the newspapers from 1973 and 1983 immediately change. Not unreasonable at all to predict FCB does not live to age 90.