In Back to the Future Part II, Doc picks up Marty in 1985 and takes him to 2015. Then old Biff realizes the Delorean is a time machine. Old Biff steals the Delorean and travels from 2015 to 1955 to give the 1955 version of himself the 2015 sports almanac.

When old Biff then returned to 2015 from 1955, shouldn't he have arrived in a way-different 2015? Instead, he arrives in the same 2015 that he departed, where Doc and Marty are still running around as if nothing changed.

Here's pic of Doc Brown in BTTF2 explaining how Old Biff created new timeline:

doc brown at chalkboard

I think this is a problem created by perspective. When Old Biff takes the Delorean back in time, we viewers do not go along for the ride. We're left hanging in a 2015 that becomes obsolete when Old Biff changes 1955. Seems our 2015 has two options: continue to exist as an alternate to the 2015 Old Biff created, or cease to exist. Either way, still seems our 2015 would be unreachable by Old Biff and the Delorean on their return from 1955.

  • 2
    So, if Old Biff faded out of existence in 2015, how did the Doc find the broken part of his cane and the almanac receipt? It was quite awhile before he found them. Not until he got back to 1985A. Wouldn't those have also faded? Even if the flux capacitor created a protective bubble, once Doc took them out of the DeLorean wouldn't they have disappeared?
    – user3965
    Commented Jan 25, 2013 at 20:22
  • Old Biff came back to 2015, and it was still the same, because Marty already got the book back from him. So, really, alternative 1985 should not have even came to be. Its all really confusing to me. Can somebody explain this part?
    – user5460
    Commented Jul 18, 2013 at 17:01
  • 6
    "If you're wondering how they eat and breathe, and other science facts, repeat to yourself, 'It's just a show, I should really just relax'"
    – fluffy
    Commented Oct 28, 2013 at 16:42
  • Biff is kind of a knucklehead. It's very possible that even with the Almanac, he'd screw up his bets. :P Didn't see the movie, so that's the best I can do. Commented Aug 15, 2016 at 14:40
  • Same as with many questions regarding Star Wars - just a bad plot. Nevertheless, BttF itself is a great trilogy :) Commented Aug 4, 2019 at 16:33

8 Answers 8


Speculation: Old Biff returns to the changed 2015 (designated 2015A). Doc and Marty "transitioned" to 2015A without noticing. Why didn't they notice? Maybe because they were out on the street when it happened and Hilldale looks the same in 2015A.

BTW, time travelers "transitioning" between changed timelines is implied by Doc Brow when he tells Marty not to worry about leaving Jennifer on the porch in "alternate 1985". After they restored the timeline Jennifer was still sleeping on the porch.*

Also, from Futurpedia:

In scenes deleted from the film, Biff Tannen of 2015 fades out of existence (much like Marty was in the original movie when interfering with his parents' meeting) once arriving in the future, having been erased from existence in that time period.

This can be explained for two different reasons:

  • First, these events created a time paradox. Having created an alternate timeline by giving his younger self the almanac, the old Biff from 2015 no longer existed, once 2015A became part of the 1985A timeline.

  • Another possibility is that Lorraine, in 1996 of the alternate timeline, shot and killed Biff.

These events are never depicted in the trilogy, although Robert Zemeckis and Bob Gale suggest this theory as a way of explaining Biff's "disappearance."

I took some screenshots from a YouTube clip:





  • 3
    +1 so Old Biff's changes to the past meant he no longer existed, causing him to fade out, just like Marty almost did in BTTF1 -- but Old Biff was able to get back in the Delorean and return to 2015 before fading out completely. I like it!
    – Shiz Z.
    Commented Oct 1, 2012 at 15:10
  • I am on verge of accepting this answer... only hesitating because the scene in this answer does not actually occur in the movie. So some might argue it is not valid. But I think I still will accept....
    – Shiz Z.
    Commented Oct 1, 2012 at 15:12
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    @ShaneFinneran - Speculation: Old Biff returns to the changed 2015 (designated 2015A). Doc and Marty "transitioned" to 2015A without noticing. Why didn't they notice? Maybe because they were out on the street when it happened and Hilldale looks the same in 2015A.
    – Oliver_C
    Commented Oct 1, 2012 at 16:48
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    BTW, time travelers "transitioning" between changed timelines is implied by Doc Brow when he tells Marty not to worry about leaving Jennifer on the porch in "alternate 1985". After they restored the timeline Jennifer was still sleeping on the porch.
    – Oliver_C
    Commented Oct 1, 2012 at 16:58
  • 1
    Biff altering the past creates a massive paradox. In 1985-A Doc was committed to a mental institution in 1983, which was 2 years prior to the events of the first movie. That means he never invented time travel, which means Old Biff could have never gone back to 1955 to make himself rich. Even if we do allow that somehow Old Biff returned to 2015-A, there's that cut scene that shows Old Biff fading away when he returns to 2015, but shouldn't the DeLorean have faded away as well? Commented Apr 18, 2018 at 18:13

In all the Back to the Future movies, a major component of the plot is reality taking time to catch up to events. Typically, this is represented as pictures with gradually changing features, which the protagonists are trying to prevent from changing. Marty's family photo in the first movie, and the tombstone in the third are examples of this.

From this behavior, we can infer it takes time for changes to propagate to the future. Otherwise, Marty would have blinked out of existence in the first movie as soon as he pushed his father out of the street; and the rest of the movies would have been... different, to say the least.

So since old Biff returned to his present as soon as he interacted with his younger self, the changes hadn't had time to take effect, yet. This is also required for Doc and Marty to go back to the 50's. In the altered future, the new Doc and Marty would neither have had the ability, nor known about the change which needed fixing.

  • 1
    But there's a difference: in both instances of slow fading, the timeline change that started the fading IS UNDONE before anyone jumps ahead to the future -- whereas Biff left his timeline change IN EFFECT and then jumped to 2015 -- so that 2015 he arrived at should have been Biff Paradise.
    – Shiz Z.
    Commented Feb 5, 2012 at 0:46
  • 3
    Also seeming to refute the "takes time to catch up" theory is how in BTTF2, just minutes after Old Biff returns to 2015 from 1955, Doc and Marty travel from 2015 to 1985, and 1985 has completely changed.
    – Shiz Z.
    Commented Feb 5, 2012 at 0:47
  • 1
    Old Biff outran the ripple, but 2015 changed just as Doc and Marty were returning Jennifer to 1985. Commented Apr 21, 2014 at 19:19
  • @ShizZ. "Both" instances? There were more than two, and some of them were not "undone". Marty and family fading out of the photo was one, but then there was the photo of Docs/Marty's/nobody's tombstone, the "You're Fired!" fax, and assorted newspaper headlines (e.g. "Emmett Brown Committed/Commended", "McFly/Gang Arrested at Courthouse" - n.b. paraphrasing here.), not to mention many other things that changed which we never saw fade (e.g. Clayton/Eastwood Ravine, Twin Pines/Lone Pine Mall), etc. Commented Oct 29, 2015 at 18:41
  • I would like to suggest that traveling in a time machine changes the traveler in fundamental ways, allowing memories that would have been erased to persist and perhaps making them resistant somewhat to physical changes caused by their own direct or indirect interference in time. We really will never know how time travel affects physiology -- I can state this with some confidence.
    – Jeff
    Commented Jan 31, 2018 at 23:36

I explained something similar to this over on the Sci-fi/Fantasy site, but this one is actually easier to answer. If the change you made in time affects the future you have to wait for it to catch up to you. An example of this is when Marty saves his dad he alters history but it takes about a week to catch up to his present and erase him from time. Even if he had jumped in the time machine and traveled back to 1985 Hill Valley he would have had to wait a week.

If you travel back into time from an altered future point (from 2015 to Biff altered 1985) the transition is instantaneous. This is because you are traveling down the time stream rather than in static time waiting for events to catch up.

At first this may seem like a contradiction but it really isn't. My belief is that the Flux Capacitor creates a temporary bubble around time travelers that allow them to be absorbed into a changed time line rather than sudden disruption. So Old Biff would not have been able to travel to future Biff ruled 1985 or even 2015 because he is such a completely different individual in those times as well as the world around him has changed so drastically. Marty was able to travel to an alternative 1985 instantly in the first Back to the Future because it was so close to his current 1985.

In other words there is one time stream in Back to the Future. It can branch and make new futures but those are eventually absorbed into the one time stream. The further it branches off from the original time stream the longer it takes for changes to catch up to current time. So the answer is the greater the change made to time the longer it takes to affect it especially if there is a possibility of correction to the original time stream.

  • There is something to this, but it ultimately doesn't hold water. It becomes magical. There are no rules to this, any plot hole can be covered by making the supposition that the time line was or wasn't altered to the extent needed for the difference. Take the 3 different 1985s. Who is to say that the Biff-hell version is less different for the starting point than the others? Both can have far reaching changes across the timeline. How does this account for time-travel duplicates? And for the fading Marty in BttF3 still seen while the duplicate doesn't fade?
    – DampeS8N
    Commented Feb 20, 2012 at 20:53
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    No it's not magical it's actually logical and one of the most logical time travel movies there is. Amazingly enough. There are no real time-travel duplicates (two of the same version from the same time) there are only older versions and younger versions of the same person. Observable differences and amount of difference that it alters the original time line is what determines the amount of time it takes for the change to happen to whatever the present is. Commented Feb 20, 2012 at 22:19
  • You say and believe that, but you haven't offered convincing evidence of that. Something can be logical and magical at the same time. It is magical because you are proposing magical physics to explain the events. Not physics based on how our real world appears to work. Time travel is muddy when it doesn't subscribe to a predetermined or divergent multiple timeline system because our universe appears to be one of these two. Marty 2 watching Marty 1 should fade too, his future is again in just as much peril. If Marty 2 is safe, so is Marty 1 by definition, and neither should fade.
    – DampeS8N
    Commented Feb 21, 2012 at 1:00
  • Marty 2 watching Marty 1 would not start to fade because his past has been secured. He has done it has happened in fact it's happening and he can see it. If Marty 1 did not succeed in getting his parents together then he would most likely instantly cease to be, there would be no fading. It's not muddy and it's not magical. The best physics example that I can think of would be Schrodinger's Cat Marty is both secured in his time line (Marty 2)and unsecured (Marty 1)at the same time. If you don't agree that's fine but like quantum mechanics just because you don't understand doesn't make it magic Commented Feb 21, 2012 at 14:07
  • Schrodinger's Cat doesn't apply here. I do understand quantum physics and the cat problem refers to unobserved objects being a collection of probabilities until observed. Marty 1 is being observed by many people, including himself. If the future one's life is secure, so to is the past's. Otherwise you are introducing a paradox. And not the silly kind that says how can you kill your own grandpa, which is resolved by either creating a new timeline OR it can't happen. Anyway, this grows too long for comments, feel free to ding me in SFF chat.
    – DampeS8N
    Commented Feb 21, 2012 at 15:12

I believe that 'Back to the Future 2' follows the same logic as the 2005 movie 'A Sound of Thunder' based on the Ray Bradbury story. In 'A Sound of Thunder' (the movie) when someone went back to the time of the dinosaurs and they made even the smallest change, and then returned to their own time, then sometime later timewaves would catch up to the present and everything would change all at once. The difference between BTTF2 and 'A Sound of Thunder' is that the timewaves were so subtle in BTTF2 that no one in 2015-B noticed them. Had Marty and Doc remained in 2015-B long enough, then reality would have changed around them into the 2015-C (Biff-altered reality). Marty and Doc left 2015-B soon enough to arrive in a 1985-C that the timewaves from 1955-C had already caught up to.


The fact that old Biff made it back to his own timeline should have been an indication to him that his plans didn't work out in the end. There were effectively two timelines old Biff created when he gave the almanac to his younger self.However, once Marty got the almanac back in the alternate 1985, there was then no longer an alternate 2015. The alternate 1985 effectively stopped once Marty was able to fix things again. So when old Biff went back to 2015, there was only one version of 2015, since by that time the alternate timeline had been closed.

Got all that? ;)

  • 1
    I understand your theory, but it seems inconsistent with how time travel works elsewhere in BTTF series. For example, when Doc and Marty realize they are in a 1985 where Biff is a millionaire, Doc says that they can't return to the original 2015 until after they undo Biff's 1955 disruption. So after Old Biff dropped off the sports almanac in 1955, and then jumped ahead to 2015 without anyone undoing anything, he should have arrived in 2015 where he had been millionaire.
    – Shiz Z.
    Commented Feb 6, 2012 at 16:48
  • @ShaneFinneran, I believe the idea is that while they are in a specific timeline, everything remains the same relative to that timeline. Only when you go back do you run the risk of crossing over into another timeline. To put it another way, once old Biff went back and created 1985 B (so to speak), Marty and Doc were still in 2015 A. Only when they went back, did they switch over to the B timeline. Once stuck in that timeline, they could not, indeed, go back to 2015, as they would then be travelling along the same B timeline. Commented Feb 7, 2012 at 9:40
  • When old Biff came back to 2015, he stayed in the A timeline, since that remained the dominant timeline, as Marty and Doc eventually went back to fix things. Had Marty and Doc stayed where they were (or had old Biff not bothered to return the time vehicle back for them), old Biff would have then been in timeline B. However, I feel that even then, he wouldn't have thought things through enough: his younger self would very likely had had old Biff killed so as not to share in his wealth. Commented Feb 7, 2012 at 9:46
  • problem with your theory is it is violated by Old Biff... he goes back to 1955 and creates timeline B, but when he travels forward, he gets right back on timeline A... which is precisely what characters CANNOT do elsewhere in the trilogy, creating much of the drama. Though you brought to mind a motivation question about Old Biff... why wouldn't he have stayed in 1955 with Young Biff, to enjoy the money when it started rolling in? Why would he have gone back to the old timeline where he was a loser?
    – Shiz Z.
    Commented Feb 7, 2012 at 16:21
  • @ShaneFinneran, let's follow your logic a bit further - if Biff had, indeed, permanently changed the future, then everything around Marty and Doc should have shifted the moment Biff left for 1955. Old Biff was a sort of time anomaly - he directly influenced his future, the same way Marty indirectly influenced his own future when Marty first went back to 1955. As such, he either should have disappeared the moment he handed over the almanac (since in Timeline B, he wouldn't have been able to go back to 1955 as Doc was at an insane asylum), or else the timeline remained stable when he left the Commented Feb 8, 2012 at 10:23

When old Biff goes back to 1955 and creates a timeline B (which is reality now), he started to fade in 1955 of timeline A after handing the magazine to his younger self. Maybe this is because he doesn't live to be that old in timeline A after he makes his younger self a billionaire. Maybe it gets him killed before he can get past 1985 and that old. In fact, Marty actually stops timeline B from happening after all.

So when he was fading back in 1955 after handing in the magazine, he thought the only way he can survive is by quickly going back to the future. But he arrives at the timeline A instead of B because he doesn't even exist in timeline B in 2015 because he gets killed long before 2015 in B.

Also he still survives in timeline A for few seconds after arriving because of the slow fading theory and because he doesn't belong to timeline A either. Because time still allows you a few minutes to correct your mistakes, Biff arrived in timeline A.

If he was smarter, he could arrive back in 2015 10 mins earlier so that he could stop himself from taking the Delorean back to 1955, thus stopping any changes or his death or go 10 mins behind in 1955 to stop himself giving the magazine to his younger self. But he was stupid and came to future where time was already changed and he didnt exist, so why A?

He had a better chance to rectify his mistakes at timeline A than in B. He was more linked to A than B because he came from A and never been to B and the Delorean also belonged to A. Marty and Doc could not go back in A because they exist in B now. Old Biff doesn't exist in either, but came to A just by the mercy of time as a chance to rectify or bring the Delorean's molecular structure to where it belonged.


(Yes, I know this topic was started over an year ago)

I didn't know about Biff's deleted scene where he fades out of existence. Because of that, this has become my point of view:

  • In BTTF1, Marty traveled back to 1955-A and changed his future, thus creating a 1985-B where he didn't exist. The future took some time to change, but since he was 30 years in the past, changes took longer to catch up to him so it took almost half the movie for him to start disappearing, giving him the chance to fix things. When his parents finally got back together, he created a new 1985-C where he did exist and also time traveled, so he stopped disappearing.

  • In BTTF2, Doc, Marty and Jennifer traveled to the future. How can their future selfs exist there if they disappeared in 1985? Because the timeline takes time to adjust like in BTTF1. If they had stayed long enough, they would have transitioned/faded into a new 2015 where their future selfs don't exist. Also, any changes they made to their future will be futile because the moment you know something about your future, you're already changing it.

  • Biff traveled back to 1955-C and drastically changed the future, thus creating 1985-D and 2015-D (we never saw 2015-D). Again, changes took some time to happen, so when he returned to 2015, it was still 2015-C. He eventually faded into 2015-D in the deleted scene (dead or alive, doesn't matter) taking much less time than Marty in the 1st movie.

  • Doc, Marty and Jennifer were still in 2015-C, but they weren't the ones responsible for the new 2015-D neither they belonged in 2015, so 2015-C only ceased to exist for them when they left in the Delorean. By traveling back to 1985, they entered the new 1985-D timeline created by Biff.

  • Since they traveled back 30 years into the past, and then another 30 years into 1955, they had enough time to fix things before starting to disappear. The Delorean didn't exist in 1985-D because Doc was in an Asylum and never created it, but since it's the only tie-in between timelines, it cannot simply cease to exist, but it could still take damage, and eventually was destroyed in BTTF3.

  • In BTTF3, Doc and Marty didn't disappear because their future was fixed, they only needed to return to it. Jennifer was left on the porch in 1985-D and when Doc and Marty shot their way into a new timeline (changing Clayton Ravine to Eastwood Ravine), she transitioned/faded from 1985-D into 1985-E while she was sleeping.

Basically, all the original plot needed to be more consistent was the deleted scene and a better explanation from Doc about the "fading", but that could become too technical for the audience.

(Edited to include all 3 movies) (edited to explain Marty's existence in the future of BTTF2)

  • "(Yes, I know this topic was started over an year ago)" - In general there is absolutely no problem in posting some new ideas to an already old question. This is a Q&A site and not a discussion forum. So if you think you have a valuable answer that might give new insights, don't hesitate to post it.
    – Napoleon Wilson
    Commented Oct 28, 2013 at 14:25
  • Thanks, that was my purpose. I just edited to justify Marty visiting himself in the future, so that practically explains all 3 movies events.
    – Johnye
    Commented Oct 28, 2013 at 16:41
  • +1 I like your in depth explanation. It's been by long belief that if you diverge time, it WILL slowly correct itself. Meaning, that time already has, sort of a path that it is going to follow. Slight changes and variations can/will and DO exist, but for the most part, you will follow your destiny, no matter what.
    – LarryF
    Commented Dec 31, 2016 at 0:11

Old Biff lest 1955 before young Biff had started to use the Almanac, or even realize its potential, so old Biff was ale to beat the ripple effect in the time machine to 2015. Remember that in the first movie, it took about a week for Marty's accidental change to the timeline to catch up with him, and that was thirty years of "new time". Now Biff has effected a change sixty years in his own past. If the ripple effect were linear, old Biff (and the original 2015) should hang around for about two weeks before changing.

When Doc and Marty travel back to 1985, they run headlong into the ripple effect and end up in the alternate timeline.

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