But… can it, though? If it changes, was what you changed still history? Or is it a new history?
Marty: Where the hell are they? Doc: The appropriate question is, "when the hell are they?"
Although we already knew going in that this was a time travel movie, this is the first time we're told about it point blank. A dog in a DeLorean vanishes, and it's not because he's been magically whisked away to Disneyland; rather, he's sent one minute into the future. And by the way, if PETA catches wind of this, Doc will wish he only had to deal with the Libyan nationalists.
Doc: He's fine, and he's completely unaware that anything happened. As far as he's concerned the trip was instantaneous. That's why Einstein's watch is exactly one minute behind mine. He skipped over that minute to instantly arrive at this moment in time.
Here's where we get the explanation, and it's setting the stage for what's to come. We're told a bit about how time travel works, but we get the information in the form of an exciting, one-minute canine journey, rather than just being lectured at in a chunk of exposition.
Stella: Oh honey, he's teasing you, nobody has two television sets.
In case you thought the 1950's were basically the same as the 1980's, only with more poodle skirts, this line should instantly dispel that opinion. The idea of having two television sets in the 1950's was unheard of. Why would you need two?
Marty: I guess you guys aren't ready for that yet. But your kids are gonna love it.
Another line that points to the cultural divide between generations. The music that, 60 years ago, was considered edgy and dangerous is now considered an "oldie." Heaven knows what those kids from the 1950's would have thought about today's music.
Marty: Damn it, Doc, why did you have to tear up that letter? If only I had more time. Wait a minute. I got all the time I want. I got a time machine. I'll just go back and warn him.
How awesome would it be to just go back in time any time we made a mistake or wanted to save someone else from making one? The possibilities are attractive…even if the downside is terrifying.