One of my favourite scenes in that film is when Marty arrives back to 1985 at the end of the movie. He races back to the mall just in time to see his earlier self jump in the DeLorean and vanish.
Or so I thought.
I realised some time ago that it's not 1985; it's 1985(i). A parallel world where the "Twin Pines Mall" is the "Lone Pine Mall". Where George(i) McFly is a successful writer, and smugly lords his success over auto-detailer Biff(i) (who, by the way, seems to be suffering some sort of severe emotional damage)
Everyone in the family is more successful. Linda(i) is omg dating and Dave(i) wears a suit! Mom(i) is younger-looking, happier and has no problems with her son driving up the the lake with his girlfriend and truck.
There's nothing missing from this perfect family picture, right?
Except Marty(i). Where's the son from this better family?
Well, you know the answer to that if you've seen the end of the movie, or read the first line of this essay. Marty got back to the mall just in time to see Marty(i) vanish in the DeLorean. That wasn't his earlier self, that was his parallel universe copy. The one who owned the truck, smugly lorded it over Biff(i) and grew up reading his father's books and stories. The man - and this is a big one - the man who Jennifer(i) fell in love with.
Whatever you think of the moral implications of Marty waltzing in and taking his doppelganger's truck, girl, and family (all's fair in Love and Time War) there's a more serious question to answer.
Where the fuck did Marty(i) go?
He didn't show up back in 1955. Marty was there twice, and didn't meet him, and there's no alternative 1955 he could have wound up in.
Did Doc(i) know about all of this, and set DeLorean(i)'s flux capacitor to a different date, so as to avoid causing the collapse of reality by having two DeLoreans arrive simultaneously in the same spot in November 1955?
Perhaps Marty(i) did go to a different year, and had his own wacky adventure. Doing so spawned another parallel world to return to, where he had *TWO* girlfriends. And a bigger truck.
Or maybe, the DeLorean(i)'s time circuits did not work at all. Doc(i) made a calucation error, and so it disintegrated completely, leaving nothing but two parallel lines of fire in the tarmac.
After all, we never saw it, or its driver, again.