FLAW in back to the Future

You should have seen this movie at least 1s now.. Well I have seen this many times now. With number of time HBO repeats this you should have seen it at least 50 times now.

In the second part Marty and the Doc goes to the future to save Marty’s son’s life. Marty buys a sport book which he thinks he take it to the past and do a little bet and get some money. But the Doc just stops him and throws the book in the trash. Old Biff from the year 2015 takes the book and hands it over to the young biff in the year 1955 without Marty’s and Doc’s knowledge and comes back. Which changes the present (year 1985). Marty’s father is been killed by Biff, his mother marries Biff and the whole hill valley town is ruined.

The FLAW:

The moment when the old biff from the future goes to 1955 and gives the book to the young biff in 1955 the time would have taken an alternate path. So the Biff should have returned to the alternate 2015 and not actual 2015. In that alternate path, Marty’s father is dead and his mother is Biff’s wife. And the city is ruined. When old Biff’s returns as well as when Marty, Jennifer and the doc leaves 2015 it would be the actual 2015 and not the alternate 2015. Marty’s father and mother will be still in Marty’s house …