4 ms·

There is also no way he could have met himself in the future. Edit: Unless the time machine was capable of visiting parallel universes.

by adam12 11y ago

serge2k 11y ago
Why not? 1. Marty leaves timeline to go to 2015 2. Marty meets Marty-F in the 2015 3. Marty returns to 1985 and grows up to be Marty-F. Of course this means that he knew, but that's okay.
- hawkice 11y ago
  A good possibility, but Back To The Future's time travel doesn't require 'immediate' consistency. Could be that changes are propagating at 2†, so Marty can meet his future self and watch him fade into a future self that is experiencing his present choices. † Because the propagation would be occurring in sec/sec, the units cancel, so it's just a number -- I jest, those aren't the same 'seconds' unit, you you see the point.
  - thaumasiotes 11y ago
    Wikipedia would have you believe that "parts per million" is a dimensionless coefficient, by a similar argument. It's not true; for example, grams of gold is not the same unit as grams of seawater.
    - hawkice 11y ago
      Indeed, their argument is belied by the old intro to Chemistry technique I learned -- start with what you know, and keep multiplying by 1, or things that are true expressed in fractions, like 3.28m/ft, stuff like that. That example fact is context-less (although it has dimension), but most aren't, so it's not "gram" as a unit, but "gram of gold in solution", otherwise you will get completely screwed up (particular if you don't specify "in reagent X" as part of the unit context -- wowzers the errors can jump out at you pretty quickly).
  - icodestuff 11y ago
    Substantially faster than 2, but somewhat inconsistently. Marty's brother started fading after only 9-10 hours. Marty doesn't start fading until nearly the week is gone. Old Biff starts fading after an hour or so? The tombstone fades immediately, and the matchbook and newspapers change within a few minutes of Marty stealing back the almanac for the last time, or possibly immediately after it's burned.
    - hawkice 11y ago
      The more I consider this the less it seems like there even IS a rate of propagation, because if it was _only_ sec/sec delays then things would change instantly, not fade in and out.
- jkarneges 11y ago
  The problem is that once he leaves 1985 to go to 2015, from everyone else's perspective he would have effectively disappeared. He (and Jennifer) wouldn't be around anymore to grow up and have a family, so there'd be no future Marty or Jennifer to visit. At most, Marty could visit his parents, who would have continued to exist the whole time and would be pretty shocked to see him after he went missing for 30 years. In order for Marty to go to the future and see himself, he'd need to continue to exist in 1985 somehow. I'm not sure how to reconcile him getting into the DeLorean with Doc and yet simultaneously going back into his house to live the rest of his life normally. A parallel universe seems like the only way for this to work, despite adding a bunch of extra complexity. It also conveniently allows old Marty to be unaware (to some extent) of young Marty's visit, because old Marty would have lived a life where he didn't take that trip.
  - jonnathanson 11y ago
    This is the most consistent explanation I've heard yet, but it doesn't seem to square with BTTF I's strong suggestion that Marty is traveling within the same universe. For instance, the fading photograph implies that whatever universe Marty visited in 1955 is causally connected to the 1985 universe in which the photograph was taken.
  - kruczek 11y ago
    > He (and Jennifer) wouldn't be around anymore to grow up and have a family, so there'd be no future Marty or Jennifer to visit. Why? They could travel to the future, meet their future selves, then travel back to the past, live their lives and in the future meet their time-travelling selves.
    - jkarneges 11y ago
      That's true. BTTF isn't normally predeterministic [1] though, but maybe the desired result could be achieved through a couple of history rewrites. For example, young Marty visits a weird future where old Marty doesn't exist, then he goes back to the original present to live normally. We can then envision a replay of young Marty's experience in the future, wherein things fade in/out around him to create a world where old Marty exists too. [1] By predeterministic I'm thinking of something like Crichton's Timeline, where the characters visit the past not to change it but to fulfil it (i.e. there is no rewriting or branching, their existence in the past is a constant).

There is also no way he could have met himself in the future. Edit: Unless the time machine was capable of visiting parallel universes.

by adam12 11y ago

There is also no way he could have met himself in the future. Edit: Unless the time machine was capable of visiting parallel universes.

serge2k 11y ago

Why not? 1. Marty leaves timeline to go to 2015 2. Marty meets Marty-F in the 2015 3. Marty returns to 1985 and grows up to be Marty-F. Of course this means that he knew, but that's okay.

hawkice 11y ago
A good possibility, but Back To The Future's time travel doesn't require 'immediate' consistency. Could be that changes are propagating at 2†, so Marty can meet his future self and watch him fade into a future self that is experiencing his present choices. † Because the propagation would be occurring in sec/sec, the units cancel, so it's just a number -- I jest, those aren't the same 'seconds' unit, you you see the point.
- thaumasiotes 11y ago
  Wikipedia would have you believe that "parts per million" is a dimensionless coefficient, by a similar argument. It's not true; for example, grams of gold is not the same unit as grams of seawater.
  - hawkice 11y ago
    Indeed, their argument is belied by the old intro to Chemistry technique I learned -- start with what you know, and keep multiplying by 1, or things that are true expressed in fractions, like 3.28m/ft, stuff like that. That example fact is context-less (although it has dimension), but most aren't, so it's not "gram" as a unit, but "gram of gold in solution", otherwise you will get completely screwed up (particular if you don't specify "in reagent X" as part of the unit context -- wowzers the errors can jump out at you pretty quickly).
- icodestuff 11y ago
  Substantially faster than 2, but somewhat inconsistently. Marty's brother started fading after only 9-10 hours. Marty doesn't start fading until nearly the week is gone. Old Biff starts fading after an hour or so? The tombstone fades immediately, and the matchbook and newspapers change within a few minutes of Marty stealing back the almanac for the last time, or possibly immediately after it's burned.
  - hawkice 11y ago
    The more I consider this the less it seems like there even IS a rate of propagation, because if it was _only_ sec/sec delays then things would change instantly, not fade in and out.
jkarneges 11y ago
The problem is that once he leaves 1985 to go to 2015, from everyone else's perspective he would have effectively disappeared. He (and Jennifer) wouldn't be around anymore to grow up and have a family, so there'd be no future Marty or Jennifer to visit. At most, Marty could visit his parents, who would have continued to exist the whole time and would be pretty shocked to see him after he went missing for 30 years. In order for Marty to go to the future and see himself, he'd need to continue to exist in 1985 somehow. I'm not sure how to reconcile him getting into the DeLorean with Doc and yet simultaneously going back into his house to live the rest of his life normally. A parallel universe seems like the only way for this to work, despite adding a bunch of extra complexity. It also conveniently allows old Marty to be unaware (to some extent) of young Marty's visit, because old Marty would have lived a life where he didn't take that trip.
- jonnathanson 11y ago
  This is the most consistent explanation I've heard yet, but it doesn't seem to square with BTTF I's strong suggestion that Marty is traveling within the same universe. For instance, the fading photograph implies that whatever universe Marty visited in 1955 is causally connected to the 1985 universe in which the photograph was taken.
- kruczek 11y ago
  > He (and Jennifer) wouldn't be around anymore to grow up and have a family, so there'd be no future Marty or Jennifer to visit. Why? They could travel to the future, meet their future selves, then travel back to the past, live their lives and in the future meet their time-travelling selves.
  - jkarneges 11y ago
    That's true. BTTF isn't normally predeterministic [1] though, but maybe the desired result could be achieved through a couple of history rewrites. For example, young Marty visits a weird future where old Marty doesn't exist, then he goes back to the original present to live normally. We can then envision a replay of young Marty's experience in the future, wherein things fade in/out around him to create a world where old Marty exists too. [1] By predeterministic I'm thinking of something like Crichton's Timeline, where the characters visit the past not to change it but to fulfil it (i.e. there is no rewriting or branching, their existence in the past is a constant).