I thought they explained it with context clues in the movie. His older brother works at Burger King, and Docs initial lab is located next to a Burger King. Since all the initial McFlys were losers I can see his brother having worked at that same Burger King for years and Marty visiting his brother at work one day might have accidentally bumped into Doc Brown in the middle of an experiment, helped him with something, and a friendship was made.
His older brother working at Burger King is definitely in the movie, but is the thing about Doc’s lab location in the movie? I’ve seen it a lot of times and I don’t remember that.
Initially, the garage served primarily as Doc’s laboratory, but when the mansion burned down in 1962, the garage became a free-standing structure that was eventually built around as Riverside Drive became John F. Kennedy Drive; by 1985, it was adjacent to a Burger King restaurant. It served as Doc’s home from that point on.
Very clearly. Well, you learn something new every day. That is the sort of economy I’d expect of Back to the Future.
So did I. I never noticed the Burger King, I had to go looking for a clip.
On a previous trip through time, Marty accidentally murdered Ray Kroc.
Nah. My hair is a lot longer.
“Whatever you do, Nas, don’t go to 2020.”
I enjoy them all but number 2 is my favorite. It mentions my Chicago Cubs.
But they were off by a year. 
What I need to know is, has there been any improvement in giant speaker technology:
Like others here, I rank them 1, 3, and 2. But it’s been years since I’ve watched any of them. In my recollection, 1 is a perfectly good standalone film, while 2 and 3 are essentially one film split into two parts.
What always messes me up, though, is the end of the first film, when Marty gets back to 1985 and watches himself go back to the past. Except that’s not himself. It’s an entirely different Marty, one who grew up with cool, successful parents and well-adjusted siblings. He has different childhood memories and likely a different personality altogether. And then original Marty simply replaces Marty2 in the new new timeline. What happens to Marty2? Does he end up in the original timeline, thereby returning to a crappier life than the one he left? Or has he now started an infinite loop of Martys replacing other Martys in timeline after timeline? And if this is the case, isn’t it conceivable that somewhere along the way there’s a Marty who never became friends with Doc in the first place? Then you have a timeline with two Martys, and a McFly family who’s lost their son forever!
It hurts my brain to think about all this, but I can’t help it.
Here’s a youtube video that prompted me to re-watch them again this year. The cast gets together to talk about the film
It’s quite an enjoyable few minutes
//i\\
This.
Nope. Remember the note that Doc has? He knows he needs to have Marty around that night so he’ll always need a Marty in 1955 to write the note; it’s a closed loop.
I worry about him, too.
He lost his girl, his truck, and who knows what else.
And Marty-prime is going to mess up sooner or later (most likely sooner, as in, immediately) by not knowing something “he” should know.
My take is he just created a new timeline that immediately replaced the one from the movie. but, the cameras are stuck in that imeline, that’s why we see it and not the new one.
I suspect Marty2 knows how to drive offload so he never crashed the car or old man Peabody’s pine breeding experiments.
PS: A bullet proof vest won’t stop AK-47 rounds.
Don’t forget the ripple effect.
NIJ Level iii
Level iii armor is a hard armor rated for rifle protection. Level iii armor is rated to withstand 7.62 mm FMJ (US military M80) rounds with a mass of 147 grains and a velocity of 2780 ft/s. Yes, level III will defeat an AK 47 round.
I don’t know if this was available when the movie was filmed but Doc might have invented his own vest or improved on existing tech.
Star Trek IV, as has been alluded to here (beginning with JAQ). The crew travels to present day earth and desperately needs something that hasn’t been invented yet (transparent aluminum). So they walk into a metallurgy shop and ask to speak to the chemist, and give him the formula. As Scotty says…“How do we know he isn’t the guy who invented it?”
In the novelization, Scotty recognizes him by name as the inventor.
Also, it was a plastics manufacturer.