[Marty and Doc notice the cops taking an unconscious Jennifer away]
They're taking her home, to your future home! We'll arrive shortly thereafter, get her out of there, and go back to 1985.
Marty You mean, I'm gonna see where I live? I'm gonna see myself as an old man?
No, no, no, Marty. That could result in a [gasps] Great Scott! Jennifer could conceivably encounter her future self! The consequences of that could be disastrous!
Marty Doc, what do you mean?
I foresee two possibilities. 1: coming face to face with herself 30 years older would put her into shock and she'd simply pass out. Or 2: the encounter could create a time paradox, the result of which could cause a chain reaction that would unravel the very fabric of the spacetime continuum and destroy the entire universe! Granted, that's a worst-case scenario. The destruction might in fact be very localised, limited to merely our own galaxy.
Marty Well, that's a relief.
Marty 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 reality [indicates the alternate reality on a blackboard, 1985A], in which Biff is corrupt, powerful, and married to your mother, and in which this has happened to me! [holds up a newspaper; the headline reads: "EMMETT BROWN COMMITTED"] 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, when, and where young Biff got his hands on that sports almanac.
Marty I'll ask him.
Marty [Western Union presents Marty with a letter from Doc] [reads the letter]
"Dear Marty, if my calculations are correct, you will receive this letter immediately after you saw the DeLorean struck by lightning. First, let me assure you that I am alive and well. I've been living happily these past eight months in the year 1885. The lightning bolt that…" [looks at the date] 1885! September 1885!
DM Delivery man
Whoa! Wait, kid! What's this all about?!
Marty He's alive! The Doc's alive! He's in the Old West, but he's alive!
DM Delivery man
Kid, you all right?! You need any help?!
Marty There's only one man who can help me!
Marty [after Marty has gone back to 1985, the Marty that came from the alternate 1985 suddenly shows up from down the street and runs to the unsuspecting 1955 Doc]
Doc, Doc! [grabs Doc, who shouts in shock] Okay. Okay! Relax, Doc! It's me! It's Marty!
No! It can't be! I just sent you back to the future.
Marty I know. You did send me back to the future, but I'm back. I'm back from the future.
Obviously, the time continuum has been disrupted, creating this new...temporal event sequence resulting in this alternate reality.
Marty 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]
Marty 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!
Marty 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.
Marty 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.
Marty 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.
Marty 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.
Marty [determined]
I'll ask him.
