Marty has always been inexplicably protected from the changes in the timeline. Thus he operates with a memory of the original timeline in which the "time machine" was never invented (or never used).

In Back to the Future when Marty returns from the past; Marty is unaware of the following changes to the timeline that his meddling has caused:

  • that his father wrote a book
  • the socio-economic status of his family members
  • the truck

These things don't make a lot of sense if Marty is traveling through time in the same universe, because the instant he changed something he should immediately be converted into the updated Marty which already knows all these things. But he isn't. Marty is just lucky he arrived in a universe where his doppelganger (the Marty native to that universe) also jumps in a "time machine" and disappears with a flash.

In Back to the Future 2 Marty travels to the future and his actions result in an old Biffy traveling back to 1955 and changing history. Subsequently When Doc Brown, Jennifer, Einstein, and Marty attempt to return to 1985 they think they are in an alter timeline. Things that suggest Marty is in parallel universes:

  • Marty encounters himself in the future, but our Marty never returns from this future, so this future Marty shouldn't exist (he should have disappeared in 1985 never to be seen again, just like the original universe from which original Marty left).
  • When Marty returns to 1985 there is another Marty in this world already. The one who is attending boarding school somewhere.
  • In this universe Doc Brown never created the "time machine" and Marty never went back in time.

I'm thinking when old Biffy went back in time, he did so to another universe, one which he changed but for which events didn't depend on the creation of a "time machine."

I'm putting "time machine" in quotes because it now seems to me that the machine really travels between parallel universes AND time.

In Back to the Future 3 Marty travels to 1885. This same Marty (and Doc Brown) have knowledge of Clayton Ravine and its history, despite their meddling which causes this future to no longer exist.

Has Marty been hopping through parallel universes all this time, never returning to his original one?


6 Answers 6


Yes, he is/has.

Futurepedia, the Back to the Future Wiki, makes a well documented case for 8 different parallel universes. In part II of the series, Doc himself explains that when one travels back in time and modifies history, a new alternate universe is created at the point-of-entry. To prevent paradoxes, the previous timeline is erased from that point on, even though their events can be remembered by the time travelers.

There seems to be some "lag" in the destruction of the voided timeline, however, as can be seen when Marty's brother ans sister, and eventually himself, only disappear from the picture after a good amount of time, and not immediately. This is because the picture is from a now defunct alternate universe and the changes need to somehow travel back to it before they take effect.

This video contains some relevant bits from the movies regarding this issue, especially the beginning where Doc traces the timeline on the board while attempting to explain the changes brought by Biff's travel through time.

  • 2
    Doc does not ever say the timelines are "parallel", the multiple timelines can be explained in terms of the idea of the timeline "changing" in some kind of meta-time dimension, as in the "type 3" time travel at xibalba.demon.co.uk/jbr/chrono.html ...in this case other timelines did exist "earlier" in meta-time, but they cease to exist when changes are made. Whereas truly parallel timelines would continue to exist even after you had changed the past and ended up in an alternate timeline.
    – Hypnosifl
    Mar 13, 2014 at 21:10
  • 1
    Also, if BTTF was explained in terms of parallel universes, then when old Biff went back and gave himself the almanac in 1955, when he returned to the future he should have returned to a different "2015-B" than the "2015-A" he had left, while Marty/Doc/Jennifer stayed in 2015-A since they were there when he left and didn't go back with Biff. But the official BTTF FAQ at bttf.wikidot.com/official-bttf-faq (written by Bob Gale and Robert Zemeckis) suggest in answer 1.9 that 2015 had actually altered around M/D/J via the ripple effect, so "original" 2015-A may no longer exist.
    – Hypnosifl
    Mar 13, 2014 at 21:12
  • So, not fully Time Travel+Causation = Many-Worlds, but with an element of The Langoliers built in.
    – Spencer
    May 16, 2023 at 14:09


Marty is not traveling to parallel universes. If he were doing so, preventing his own birth in parallel universes would cause no paradox. In the movies, when he has failed to correct the disturbances he causes, he starts to become translucent and "fade away". This would not be the case in a parallel universe, where causing an alteration to the past would merely prevent a parallel doppleganger from being born.

  • 1
    good point, but then his memories should keep chaning all the time. Apr 8, 2013 at 19:02
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    Strictly speaking this would be true, but we've already seen that he has hours or days to correct alterations. It could be that memories lag even further. Additionally, since it was written for mass appeal, the finer points of logic might be glossed over so as not to confuse less sophisticated viewers, certainly it could have impacted the popularity of the film to include such details.
    – John O
    Apr 8, 2013 at 19:06
  • It is true that the parallel universe does not explain the changing photographs. Apr 8, 2013 at 19:07
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    The memories must lag quite a bit behind indeed then. From the end of BttF1 to the end of BttF3 at least a week had passed (roughly the same amount of time Marty spent in 1955 in BttF1), yet Marty never give any indication that he suddenly "remembers" his changed 18 years, growing up with his altered parents from BttF1.
    – Xantec
    Apr 8, 2013 at 19:14
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    Also, not all changes are slow moving. When Marty's father took back his mother on the dance floor, Marty immediately sprung up whole and the picture was completely restored. Logically the restoration should have taken the same amount of time as the dissolution, and during that time Marty then could have then been altered along with everything else.
    – Xantec
    Apr 8, 2013 at 19:16

I suppose the flux capacitor keeps him from the very likely overwelmimg disturbances his actions in the past are causing. But apparently his memories never catch up, so yes I think he keeps reappearing in different parallel universes, just as Doc explains the obvious 1985A parallel universe.

The Doc even explains the time machine can only travel back and forward along the timeline (TM). So if his actions cause other turns to be taken by individuals, the time machine has to follow these new paths.

  • 2
    Doc Brown wasn't a particularly good inventor. And even when he hit upon one that worked (the time machine) he had to spend his entire fortune to build it. Considering the first test of the machine was with Einstein in BttF1, I wouldn't really call the Doc an expert on what it could or couldn't do.
    – Xantec
    Apr 8, 2013 at 19:19
  • @Xantec Oh, he wasn't? The insanely precise rifle, the fridge, the reverse engineered micro chip, the adaption of the futureistic Mr. Fusion and two(!) aggressively loving time machines, and you dare implying he is not good at what he does, just because he is not churning out movie-worth inventions like a factory? I wonder how many big break throughs, in the order of magnitude of time machines in 1985, the average sucessful scientist has in their live. Sep 26, 2018 at 7:22
  • Correct, he wasn't a good inventor. He was a good scientist and engineer, but aside from the time machine everything you've listed was invented by someone else.
    – Xantec
    Sep 26, 2018 at 11:16

In many stories pertaining to time travel, it is usually assumed that the traveler is somewhat protected from alterations and changes that they inadvertently make, due to the fact they are simply a visitor. So technically memories shouldn't change (look at Time Cop), but then again, shouldn't Marty also be protected from disappearing from the first one if his parents didn't hook up?

  • I think you're on the right track with the first portion of your answer, but you should remove the part where you start asking your own question. Open a new one if you feel it is distinctly different enough to warrant it.
    – phantom42
    May 7, 2013 at 15:20

No, No, a thousand times No!

..if you mean, are there multiple co-existing universes?

At no point in the trilogy is it suggested that new universes are created (and the old ones continue to exist) every time they travel back in time. This would destroy the entire plot and purpose of the movies!

There would be no need for any of the urgency in that he has in putting things to right (e.g. getting his parents together or preventing Biff getting the Almanac, etc.), the movie would be about getting him back to his own universe. And as John O said, preventing his parents meeting would not endanger his existence. But that's what the films are all about! (Never, "how am I going to get back to my own universe?", like in Sliders)

In BTTF 2, the Doc does draw a diagram of the timeline splitting into two, but this is more an illustration to show Marty (and us) how the timeline diverged from the "correct" one, rather than meaning to imply that there are now two co-existing universes.

Now you do ask why they remember life from their own timeline. The movie treats a time-traveller's memory as sacrosanct in this case, for the purposes of story telling - they always remember the history of the timeline they came from, but this only applies to time travellers' memories. It doesn't apply to (say) the newspapers, fax-printouts, photographs or matchboxes or anything else that they bring with them - these all change to keep up with the changes in the timeline even though they should not if they came from a parallel universe.

In this case, we just have to accept that one of the movie's rules of time-travel is that a person's memory is special - this is consistent throughout the trilogy.


Personally, I didnt see the sequels to Back To The Future because I firmly believe that any possible time travel creates or justifies alternate universes/simultaneous existances, which I believe people in real life go through but dont know about ... (Hopefully, after our physical death)

You have two Martys ... one in Universe A that has depressing parents but is connected to Doc Brown ... and another in Universe B, who through Doc Browns time machine, and the courage to help his father become stronger and win his mothers love, has a better life with stronger parents, who know secretly, what their son will help Doc Brown do ...

When we see Marty come back from the past to the future at the end of the first film, he is watching Marty in Universe A but comes home in Universe B, thinking its the same when it isnt ...

  • 1
    Hi, welcome to SF&F. You may personally believe that any time travel creates parallel universes, but do you have any evidence that the writers/creators of the movies intended that this would be the case? Please support any personal theories with evidence from the movies or from other public statements from the creators.
    – DavidW
    Jun 19, 2020 at 22:03

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