In Back to the Future 2, How does Marty and his girlfriend travel into the future, see their future selves and not remember traveling before? I don’t really know the rules of time travel, maybe the SD has it down.
This could be a hypothetical question but then again I still believe the Abyss was based on a true story.
Reported for forum and title change.
Messin with the space time continuum man…
Moved to Cafe Society, and title edited to indicate subject.
Colibri
General Questions Moderator
Sorry about the wrong section and vagueness of the title… dually noted
In the future that Marty and Jennifer traveled to in BTTF2, they hadn’t yet traveled to the future, so their future selves had no idea they’d see them.
And at that point, Jennifer had never time-traveled (and didn’t even know the Delorean existed), thus the screaming.
EDIT: You’re not thinking fourth dimensionally!
Changes to the timeline in the BttFverse have propagation speeds; for example, in the first movie, it takes about a week for a fairly major change to propagate 15 years into the future. (The sequential fading of the McFly siblings from the photo suggests that they began fading as the changewave passed their birth dates.) My personal theory is that the propagation speed is inversely proportional to the scale of the changes, so a minor change would probably propagate more quickly.
Going to the future, observing and possibly meddling a bit, then returning to your present and never acting on the information obtained from your trip would constitute a pretty minor change to the timeline. The change from future-Marty not remembering the trip to remembering the trip might thus propagate more quickly than Marty’s self-deletion, but it also had farther to go. It’s plausible that the changewave introduced by their departure for the future simply hadn’t reached 2015 yet. If Doc and Marty had hung around the future for a few days, it’s possible that future-Marty would come to have always remembered the trip. At that point, he would know where they were at all times, and could go meet them, if he chose. (Doc would undoubtedly disapprove of such a meeting, however.)
It’s also possible that the changewave didn’t actually start propagating until they returned to their present; there are indications that time travelers are somewhat dissociated from the timeline during their travels.
“Rules of Time Travel”? The only rule of time travel is, “Time travel works the way the writers say it works.”
I have two theories:
One, backward time travel is impossible, as you can’t just “jump” from one time to another, but have to pass through them as if it is a dimension, and if you try to move backward, you will bump into yourself from (e.g.) one-one millionth of a second in the past.
Two, when you go back in time, you are now in a “parallel universe”; everyone who was with you just saw you disappear, and any changes you make in “the past” will not affect them. (Spock in the latest Star Trek movie is an example; in the universe he left, Vulcan is still there, decades after it was destroyed in the universe he is in now.)
Here’s an example of how “rules of time travel” aren’t constant; in one of the movies (the second one, I think), when Marty is in the 1950s and burns the book of sports results from the future, it has an immediate effect (presumably because Biff would then never be able to make the horse racing bets he did to start his bankroll); also, in the third movie, when Marty does not participate in the drag race and subsequently does not run into another car, all of the “You’re Fired!” messages from the future suddenly disappear (actually, the paper is still there, but the words just disappear off the page).
Are you sure it’s not, “Do not talk about time travel?”
Anyway, the future selves seen by Marty and his girlfriend are what’s going to happen to them if they don’t alter their future - which means that the versions of themselves that they’re seeing never traveled into the future. If they had, they wouldn’t be living such shitty lives.
Time machines not only do not but cannot exist. Larry Niven proved this logically. We’re not talking the abstruse concept of causality violation but simple nested either-or two-value dichotomies.
Like this:
In any theortetical structure of the universe, time machines either can or cannot exist. If they cannot, QED, so explpore “can”.
In a universe which permits time machines, such machines either can or cannot permit the past to be changed. One which does not permit change differs in no significant way from any other increase in available information, e.g., the Nag Hammadi scrolls or the Internet. Therefore explore “can change.”
In any universe in which time machines capable of effecting changes to the past are possible, such a machine either will be or will not be built and used. If “not”, no time machine, so explore “will be built.”
Any time machiine capable of effecting a change in the past which is in fact built and used will thereby reset the universe, potentially back to step 1, at minimum back to step 3.
A reset universe which still permits construction of a time machine capable of effecting change to the past will thus have to pass through the criteria above again, and if it makes it to step 4, will again recycle. Each time the odds of a time machine capable of changing the past being possible, built, and used diminishes to some degree – how much does not matter.
The net result is that any universe which permits construction of a time machine capable of changing the past will eliminete itself from the sheaf of possible universes, by cycling until either such a machine is impossible, such a machine cannot cause change, or such a machine is never built.
QED
I was referring to “the rules of time travel” in the same context of rules for surviving a zombie apocalypse. The writers put a lot of thought into covering all the angles, this specific instance I was wondering how they made sense of it.
I didn’t want to scare off the OP by talking about temporal hysteresis, but that’s part of my theory. It’s established in the first movie that reversions propagate much more quickly than new changes. Once the George/Lorraine relationship is restarted, we see Marty fade back in–both in the photo and in person–very quickly. Similarly, destroying the book so Biff can’t get it back results in the timeline quickly reverting to its previous state.
The changing fax is a bit more complicated, but it stems from the fact that refusing to race wasn’t actually the change that caused it; that was a symptom of the change. The fax faded because of a change in Marty’s character that happened while he was in 1885–learning not to be taunted into rash actions when someone calls him “chicken”. That change would have begun propagating as soon as he returned to 1985 from 1885. He had been there long enough to walk from the ravine to Jennifer’s house and wake her, return home, then take Jennifer out for a ride in the new truck; this all happened the same day, but it was evidently just long enough for the change to propagate to 2015. That’s not implausible, given that it was a much more minor change than erasing several people from the timeline. The circumstances of the near-wreck reminded Jennifer of the fax, so she pulled it out and looked at it just as the changewave caught up to the point where future-Marty got fired. Since future-Marty wouldn’t have been taunted into joining Needles’ scheme, he wouldn’t have been fired, so the message faded off the paper.
Refusing to race, and thus avoiding the wreck, would have triggered a secondary changewave. This one–assuming Lorraine was correct about Marty’s potential musical career–would have resulted in him becoming a musician, rather than a businessman. That would change his 2015 circumstances more drastically; it’s likely that he would have been living in a different place, among other things. That piece of paper would probably still have existed, and might have wound up in the same fax machine, but unless the alt-future residents of that house received a fax on it before the point at which Jennifer took it, it would remain blank. (Conceivably, if they got more faxes than future-Marty originally did, it could change to bear a completely unrelated message, meant for someone Jennifer will never meet.)
touche… good answer
Years and years ago Michael J. Fox was on Letterman (I think promoting BTTF:II or III) and he mentioned that sometimes fanboys would approach him with these sorts of questions and theories. He said he’d just smile and say, “Sorry, they pay me to say things and move around, can’t help you with any of that…”