Yeah that's a flaw in the movie. It doesen't have many and I would assume they knew it but hoped nobody would notice it. Funny becuase Doc does that whole chalkboard explaination "somewhere in the past the timeline SKEWWWED into this tangent, creating this alternate 1985. Alternate to you, me and Einstein, but reality for eveyone else"... you would think someone would pick up on it (yes I did at 13-years-old, but I pay too close attention to movies), but not alot of people do.
In order to get around this they would have had to change the story so that they didn't destory the time machine at the end of Part 3, bury it again or something and find it in 2015. Something to that effect.
Also, how the fuck does Biff, who is constantly portrayed as a complete idiot, know how to use the time machine? He would have even had to know how to use Mr. Fusion to get back.
On a side note: Hover Boards are real! Watch the making off! I want one! They must be somewhere. I must find them!
<message edited by Lomox on Wednesday, September 07, 2005 12:00 PM>