Back to the future:
Marty: This can't be happening! (reads) March 15th 1973? No, oh please God no, no, please God, please God, no, this can't be happening! This can't be happening! This can't be.....
A shadow appears on the gravestone. Marty hears a twig snap and turns around. It's DOC and EINSTEIN!
Doc: I'm afraid it is happening Marty, all of it!
Marty: Doc!
Doc: When I learnt about your father, I figured you'd come here.
Marty: Then you know what happened to him? You know what happened, March 15th 1973?
Doc: Yes Marty, I know.
Cut to Doc's garage. It's a mess. Doc opens a book - Hill Valley Telegraph Archives March 1st - April 30th 1973. On the page he turns to is a headline - "George McFly Murdered: Local Author Shot Dead." We stay focused on the paper as Doc speaks.
Doc: (v.o) I went to the public library to try and make sense out of all the madness. The place was boarded up, shut down, so I broke in and borrowed some newspapers.
The camera turns to Marty and Doc.
Marty: I don't get it Doc, I mean how can this be happening? It's like we're in hell or something.
Doc: No, its Hill Valley, although I can't imagine hell being much worse!
Einstein whines. Doc takes a candle and goes over to him.
Doc: Oh Einie, I'm sorry boy, the lab is an awful, awful, awful, awful mess!
Doc gets Einstein's basket and he gets inside.
Doc: Atta boy. (to Marty) Obviously the time continuum has been disrupted creating this new temporally venced sequence resulting in this alternative reality.
Marty: English, Doc!
Doc: Here, here, here, let me illustrate.
Doc finds blackboard and stands it up. He picks up some chalk.
Doc: Imagine that this line represents time.....
Doc draws a line on the blackboard.
Doc: ...Here's the present, 1985 (He writes "1985" on the board), the future (he writes "F"), and the past (he writes "Past"). Prior to this point in time... (He points to 1985) ...somewhere in the past, the timeline skewed into this tangent, creating an alternate 1985.
Doc draws the tangent on the board and writes "1985-A" on it.
Doc: Alternate to you, me and Einstein. But reality for everyone else.
Doc goes to the DeLorean and gets a bag out.
Doc: Recognise this? It's the bag the sports book came in. I know, because the receipt is still inside. I found them in the time machine, along with this!
Doc shows Marty what he found. It's the top of 2015 Biff's cane!
Marty: It's the top of Biff's cane, I mean old Biff from the future!
Doc: Correct! It was in the time machine because Biff was in the time machine - with the sports almanac!
Marty: Holy shit!
Doc: You see, whilst we were in the future, Biff got the sports book, stole the time machine, went back in time and gave the book to himself at some point in the past.
Doc draws a line from the "F" on the board to the point where the tangent skewed into 1985-A. He then takes out a copy of the Hill Valley Telegraph, "Hill Valley Man Wins Big At Races". Next to it is a picture of Biff.
Doc: Look! (chuckles in a "how simple!" style) It says, right here, that Biff won 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 in his pocket with a magnifying glass.
Marty does so. He sees the almanac in Biff's pocket.
Marty: The almanac! (Doc chuckles again) That son of a bitch stole my idea!
Marty slams his fist on the table.
Marty: He must have been listening when I..... it's my fault! If I hadn't bought that damn book, none of this would ever have happened!
Doc: Well, that's all in the past.
Marty: You mean the future.
Doc: 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 almanac.
Doc: We can't! Because, if we travel into the future from this point in time, it will be the future of this reality! (He underlines 1985-A on the board). In which Biff is corrupt, and powerful, and married to your mother; and in which this has happened to me!
Doc shows Marty another paper. The headline says "Emmett Brown Committed - Crackpot Inventor Declared Legally Insane." A side story says "Biffco To Build New Dioxin Plant" and "Nixon To Seek 5th Term." Einstein whines as Marty takes it.
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 the specific circumstances of how, where and when, young Biff got his hands on that sports almanac.
Marty: I'll ask him.
Spaceballs:
DARK HELMET
(mask down) Have you found them yet?
CORPORAL
No, Lord Helmet. They're still not on the scanners.
DARK HELMET
Well, keep looking for them. (drinks coffee through his mask)
COL SANDURZ
Pardon me, sir. I have an idea. Corporal, get me the video cassette of Spaceballs-the Movie.
CORPORAL
Yes, sir.
CORPORAL walks to a wall labeled, "Mr. Rental." The wall opens. He looks through the selections.
DARK HELMET
Colonel Sandurz, may I speak with you, please?
COL SANDURZ
Yes, sir.
DARK HELMET
(lifts up mask) How could there be a cassette of Spaceballs-the Movie. We're still in the middle of making it.
COL SANDURZ
That's true, sir, but there's been a new breakthrough in home-video marketing.
DARK HELMET
There has?
COL SANDURZ
Yes. Instant cassettes. They're out in stores before the movie is finished.
DARK HELMET
Naaaaa.
CORPORAL
Here it is, sir. Spaceballs.
COL SANDURZ
Good work, Corporal. Punch it up.
CORPORAL
starts the tape. It starts on the FBI Warning.
COL SANDURZ
Started much too early. Prepare to fast-forward.
CORPORAL
Preparing to fast-forward.
COL SANDURZ
Fast-forward.
CORPORAL
Fast-forwarding, sir.
He Starts fast-forwarding through the ludicrous speed scene. Helmet is thrown into the panel at a high-speed.
DARK HELMET
Nnnnno. Go past this, past this part. In fact, never play this again.
COL SANDURZ
Try here. Stop.
The movie stops at the exact same thing that is actually happening now. DARK HELMET looks at the camera, then he turns back to the monitor. COL SANDURZ looks at the camera when DARK HELMET looks back at the monitor, then he looks back at the monitor. DARK HELMET looks at the camera when COL SANDURZ looks back at the monitor. When DARK HELMET turns back, he waves his hand. He turns back to the camera.
DARK HELMET
What the hell am I looking at? When does this happen in the movie?
COL SANDURZ
Now. You're looking at now, sir. Everything that happens now, is happening now.
DARK HELMET
What happened to then?
COL SANDURZ
We passed then?
DARK HELMET
When?
COL SANDURZ
Just now. We're at now, now.
DARK HELMET
Go back to then.
COL SANDURZ
When?
DARK HELMET
Now.
COL SANDURZ
Now?
DARK HELMET
Now.
COL SANDURZ
I can't.
DARK HELMET
Why?
COL SANDURZ
We missed it.
DARK HELMET
When?
COL SANDURZ
Just now.
DARK HELMET
When will then be now?
CORPORAL rewinds the tape. He stops at the point when LONE STARR, BARF, VESPA and DOT are walking through the desert.
COL SANDURZ
Soon.
DARK HELMET
How soon?
CORPORAL
Sir.
DARK HELMET
What?
CORPORAL
We've identified their location.
DARK HELMET
Where?
CORPORAL
It's the Moon of Vega.
COL SANDURZ
Good work. Set a course, and prepare for our arrival.
DARK HELMET
When?
CORPORAL
Nineteen-hundred hours, sir.
COL SANDURZ
By high-noon, tomorrow, they will be our prisoners.