So, in Back to the Future Part II, Biff steals the time machine in 2015 and gives his 1955 self future knowledge, causing the timeline to change and create 1985-A, in which Marty has been shipped off to Switzerland and Doc Brown has been committed to a mental institution. The question is, what happened to these versions of Marty and Doc when the time-travelling ones from the original 1985 arrive? Did they fade away or would it have been possible for Marty and Doc to meet their alternates?

Note that this is a different situation from 1985 Marty coexisting with 2015 Marty, as they are from two different time periods. Marty and Marty-A should be about the same age, though Marty would be about a week older if Marty-A never went back to 1955, which is likely if Doc-A were committed in 1983, as the newspaper implied.

This brings up interesting ramifications for Jennifer, as the Parkers apparently live in the same house in 1985-A. It might have been possible for Jennifer-A to find herself on her porch!

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    If you look through recent questions, I think you will find some very similar ones with answers that might satisfy you. – rosesunhill Mar 16 '16 at 20:42
  • Here's one: scifi.stackexchange.com/questions/122189/… – rosesunhill Mar 16 '16 at 20:43
  • @rosesunhill, that's not a similar question. But I will admit that Part II is the most confusing of the trilogy, which is why there are so many questions about it. – John Sensebe Mar 16 '16 at 22:18
  • Okay, I understand that pov. I don't have all the BTTF questions/answers immediately at my mental tips, but I had the impression that most answers viewed the in-universe as overwriting previous timelines, which would seem to eliminate the possibility of meeting an earlier self. Still, Marty did slowly fade out of the photograph, so maybe you're on to some time, I mean something. One Jennifer might have watched her other self slowly appear. – rosesunhill Mar 16 '16 at 22:26

Inspired mainly by this answer (but interpreting matters somewhat differently) I'm going to say that Marty-A and Doc-A never existed. Instead, the universe reformed itself around Marty and Doc, including people having memories of interacting with them in ways that never "actually" happened.

While the differences weren't quite so extreme, the same thing happened at the end of the original BTTF. For example, Lorraine remembered talking to Marty about his planned camping trip with Jennifer, a discussion he never had.

  • That isn't actually the same logic as my answer which you're citing. I didn't mean to suggest that any false memories are created when the timeline re-forms around someone, it's just that when history was over-written by old Biff's actions in 1955, the Marty/Doc/Jennifer in 2015 were not over-written because they were time travelers. But my idea is that there is still a complete history covering every point in time between 1955 and 2015, which would naturally include a version of Marty who grows up without a father since Biff killed George in 1973. – Hypnosifl Mar 16 '16 at 23:22
  • One way to think about the "complete history" issue: imagine someone (say, aliens) had been secretly recording everyone in Hill Valley 24/7 from 1955 on, and storing all the recordings somewhere. If history is changed, then all those recordings should change too, just like photos do. So in 1985A, wouldn't all the recordings show Marty growing up in the alternate timeline with his dad dead and his mom marrying Biff? If the recordings were being done 24/7, how and when would the recordings show this different Marty "becoming" the Marty who arrived in a flying DeLorean? – Hypnosifl Mar 17 '16 at 0:04
  • @Hypnosifl: I've rephrased so as to not misquote you. I prefer my interpretation (and logical consistency be damned, if necessary!) because otherwise we're left with pretty horrible implications. Not that I necessarily mind horrible implications in more dramatic works, mind you, but I'd rather continue to think of BTTF as light comedy and multiple genocide kind of detracts from the mood. :-) – Harry Johnston Mar 17 '16 at 1:12
  • Yeah, I understand that--personally I don't think of it as the alternate versions getting destroyed, just as their memories getting replaced while their identities or "souls" or something remain intact, but I guess that's still kind of creepy in its own way... – Hypnosifl Mar 17 '16 at 3:28

I actually just discussed this one in the course of a very long answer I happened to post a couple minutes before you posted this question. We have no direct onscreen evidence, but in the answer to question 1.19 from the Official BTTF FAQ, Gale and Zemeckis discuss the idea that in the BTTF universe there is a "self-preservation instinct of the spacetime continuum" effect that tries to nudge history back on track when it changes. And in my answer I talked about my speculations about what might happen if history was changed too drastically for this to work, I'll just quote the relevant section below:

What happens if the timeline is too badly altered to ensure that a certain time trip can happen "naturally"? For example, in the "1985A" version of history where Biff is rich and powerful (timeline 4 and 5 on the above chart), Doc has been put in a mental asylum, so unless he escapes and gets the money for equipment, he presumably can't build a time machine. Also, Biff says at one point to Marty "You're supposed to be in Switzerland you little son of a bitch!", indicating that the Marty who grew up in that timeline--let's call him Marty-A--was supposed to be abroad on that date. So it seems unlikely that the self-preservation effect could have ensured that Marty-A would meet up with Doc-A at the location of the Lone Pine Mall (if it even still existed in this timeline) and travel back to 1955 in a DeLorean time machine provided by Doc-A. In general we know the self-preservation effect can't be perfect since if it was there would be no danger of a time traveler erasing themselves from existence by changing the past.

One possibility here is that the "laws" of the BTTF universe would allow two alternate versions of Marty at the same biological age to coexist in a single timeline (with Marty-A still in Switzerland while the Marty from timeline 1 confronts Biff). Another is that Marty-A would simply be forcibly pulled out of time on Oct. 26 1985 of this altered timeline (perhaps along with a DeLorean sitting in a garage somewhere) and would spontaneously jump to 1955 with all memories and physical appearance reset to those of the Marty of timeline 1 upon arrival. This would be a sort of brute-force method the universe could ensure there is only a single version of Marty at each biological age (and biological age seems to be important in the BTTF universe, since the answer to question 1.8 in the official FAQ mentions they had wanted to have old Biff disappearing upon returning to 2015, because in the new altered history he had died at a younger age than the old Biff we saw).

If the brute-force method seems weird, note that there actually is precedent for it in this early BTTF script draft written by Gale and Zemeckis. In this version of the script, the changes Marty made in the past (1952 in this version) had more drastic effects on his present--when he returned to his own time he found a world filled with Jetsons-style retro-futuristic technologies, some labeled as being products of "E. Brown Enterprises", since Doc's experiences with Marty in 1952 led him to abandon time travel as too dangerous and focus his inventive skills on other things. So if the Doc of this timeline never built a time machine, what happened to the Marty who grew up in this timeline? Doc explains that he just disappeared on the appropriate date:

MARTY But if you didn't rebuild the Time Machine, how did I go back in time in the first place?

PROF. BROWN According to your girl friend, Suzy Parker, you and she were at the movies. You went to the restroom, and you never came out. Obviously, you stepped through an inter-dimensional time warp, created by the original operation of the time machine.

  • I think it can be simpler than that; see my answer, based on some of your earlier observations. – Harry Johnston Mar 16 '16 at 23:15

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