2. Why Did Marty Not Start To Disappear Earlier In The Film?
As mentioned before, time travel is a tricky subject to put over on screen. Establishing how it works can lead to inconsistencies, and Back To The Future has a load of them, and the way the films showed changes in time taking effect is one of these inconsistencies that makes little sense. In Part One we see Marty look at a photo of himself with his brother and sister. As the film progresses, starting with his eldest sibling they all start to disappear, effectively fading away from time. Later in parts Two and Three we see newspapers headlines, faxes and photos of grave stones magically alter themselves to reflect changes in time. The inconsistency comes in that other than the photo of Marty and his siblings all of the other changes are instantly. And whilst these instant changes are obviously just the simplest way to show the audience what has happened, they do nevertheless highlight a flaw in the way time is altered throughout the series. When Marty burns the sports almanac at the end of part two we see headlines instantly change to see that George McFly no longer dies and that the Doc is commended rather than committed. If changes in time are instant in their effect it suggests Marty wasted a lot of time trying to put things right in Part One when he didnt need to. These swift changes suggest that Marty's continued meddling in time in Part One was the reason his brother and sister continued to vanish from the photo. Had he left well alone after just his brother's hair disappeared he could have expected to return to 1985 t at worst find Dave was bald on top. The slow progression of change to the photo means that time was probably going to put itself right or Marty should have instantly vanished the moment he pushed his father from in front of that car.