Back to the Future has one flaw
In the first movie, when Marty is playing songs at prom, and his parents are not really hitting it off, he starts to fade away...as well as his family in the family photo he carried.
This suggests a singular timeline, since if his parents don't get together he will never be born and thus fade away.
HOWEVER, in the sequel where Biff gets sports almanac and then makes it rich, they return to a timeline where Biff is all powerful, and the Doc never invented the time machine...
If, then it was a singular timeline, then Marty could not have time traveled and thus would have faded away...
The fact that they appeared in this alternate timeline makes me believe it is suggesting a branching timeline where each decision point in time generates infinite universes
Head explode.
