Flying Spaghetti Monster wrote:
Of course they can always say that Doc Brown will eventually go to the future and introduce these devices (like iPhones) into the 80's and the 50's.
Oh wait, in order for that to work, we'd have go with the Bill and Ted theory of time travel where all future interference happens in one single timeline!
Which, really, is how it'd probably "really work" because we ARE in one timeline. Anything that's happened in the past has already happened even if it involved stuff that HASN'T happened yet. Which actually can fuck with the mind when it comes to free-will. Of course this brings into some question about the future's motivations for "saving" Bill and Ted since they'd likely know how time travel works, unless they knew Rufus had to go back to help them to ensure things, but... Bah!
Anyway, the key to how Bill and Ted treated this comes both with the stuff with Ted's father's keys and the stuff at the Circle-K. There's a minor plot thread in the beginning of the movie with Ted's father looking for his keys, we later discovered that Ted stole them by going into the past at some point in the future, stealing them, and hiding them for him and Bill to use to save the historical figures. Then, of course, we see Bill and Ted arrive at the Circle-K and the interaction there before Bill and Ted have left, or even realize what is going on.
It's really a very, very, beautiful use of time-travel.