Obviously, the time continuum has been disrupted, creating this new...temporal event sequence resulting in this alternate reality.
English, Doc.
Here, here, here. Let me, uh, let me illustrate. [brings over a chalkboard] Imagine that this line [draws a straight line across the board] represents time. Here's the present, 1985, the future and the past. [writes "Past" on left side, "1985" in the middle, and "F" for Future on the right; points at the area before 1985] Prior to this point in time, somewhere in the past, the timeline [draws another line] skewed into this tangent creating an alternate 1985. [writes 1985A on chalkboard] Alternate to you, me and Einstein, but reality for everyone else. [pulls a small, silver plastic bag out of the DeLorean] Recognize this? It's the bag the sports book came in. I know, because the receipt was still inside. I found them in the time machine...along with this. [shows Marty a small-fisted object]
It's the top of Biff's cane. I mean, Old Biff from the future.
Correct. It was in the time machine because Biff was in the time machine, with the Sports Almanac!
Holy shit.
You see, while we were in the future, Biff got the sports book, stole the time machine, [draws an overarching line across the chalkboard] went back in time, and gave the book to himself at some point in the past. [brings over a large newspaper] Look. [scoffs] It says right here that Biff made his first million betting on a horse race in 1958. He wasn't just lucky. He knew because he had all the race results in the Sports Almanac. That's how he made his entire fortune! Look at his pocket with a magnifying glass.
The Almanac. [angrily] Son-of-a-bitch stole my idea! He must have been listening when I-- [realizes; shocked] It's my fault. The whole thing is my fault. If I hadn't bought that damn book, none of this would have ever happened.
That's all in the past.
You mean the future.
Whatever! It demonstrates precisely how time travel can be misused, and why the time machine must be destroyed, after we straighten all of this out.
Right. So, we go back to the future, and we stop Biff from stealing the time machine.
We can't, because if we travel into the future from this point in time, it will be the future of this... [indicates 1985A on the blackboard] reality, in which Biff is corrupt, and powerful, and married to your mother, and in which... [holds up a newspaper; the headline reads: "EMMETT BROWN COMMITTED"] ...this has happened to me! [Einstein moans, and Marty takes the newspaper from Doc] No. Our only chance to repair the present is in the past, at the point where the timeline skewed into this tangent. In order to put the universe back as we remember it and get back to our reality, we have to find out the exact date and specific circumstances of how, where, and when young Biff got his hands on that Sports Almanac.
