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Actually, Marty Didn’t Go Back to the Future: Graphing the Train Scene of BTTF3 (francoismaillet.com)
98 points by ddcarnage on Nov 4, 2015 | hide | past | web | favorite | 45 comments



Well I saw the movie, and Marty did make it back to 1985. The problem is that the analysis assumes that every second in the film corresponds to a second in real life. That's not true, the shots overlap in real life but are shown after one another in a sequence to make showing what happened (possibly at the same time) more practical. This overlapping is often used in dramatic representations of real events in movies.

One hint is when the author notes that acceleration happens much more quickly during the few short shots when the speedometer is visible, i.e. the acceleration is much quicker compared to the assumed linear acceleration in-between those shots.

It would be an interesting project to analyse the sequence of shots and figure out which ones overlapped by how much, to make the time/distances/accelerations work out. [Edit: copyediting]


OP here.

You're probably right it's not all real time. I figured it wasn't completely unreasonable to treat it as such because when you watch it, most of it does feel RT and we pretty much see everything that happens in an uninterrupted way.

But for the sake of argument, even if the analysis is skewed a bit, it does suggests they were missing a lot of tracks. So if some of the sequence can be considered RT and some of it not, for them to reach the 88 mph in under 3 miles, probably a lot of it would need to be non-RT, which didn't feel right to me based on the way it's presented in the movie.

Totally agree it would be awesome to be able to figure out what overlaps. Thanks for the comment!


;) A classic example that exaggerates the different passing of time of movie vs real time happens in Monty Python and the Holy Grail: https://youtu.be/DPXG4pdPj4w?t=20s


Went to school for video/film production and time compression was the subject of a couple of fun projects. In TV and movies, you rarely see things in "real time" unless it's specifically done for an effect (like the gimmick of "24" or to create some level of tension).

Normally, you compress time to a greater or lesser degree because you just don't need to see every single action that someone takes in the course of a given hour or event. Like you point out in the Python clip, you wouldn't normally shoot the entirety of a guy running across a long field. You'd show him start running, cut to a closer shot with him making progress, cut to the person/place he's running toward for reaction or to re-establish the destination, and then cut back to the guy as he's getting there.

When you drag these kinds of things out, it can be a good gag because it's almost like a bad storyteller who includes every irrelevant detail. It makes us uncomfortable and throws off timing. In a more tense scene, time is often screwy because maybe you want to drag things out and show all of the characters' reactions to create anxiety and the feeling that "they'll never make it".

Anyway, thanks for the reminder about the Python bit. Always makes me smile :)


This is also something used in fight scenes, where a person will say, throw a punch, then the camera angle shifts, and the person will be seen to throw the punch again - "The Asian Cut" [0]

[0] https://www.youtube.com/watch?v=Z1PCtIaM_GQ


I love the little touches. Guard: "hey..."


It's more than just non-overlapping scenes. Most movies play very loose with time, drawing it out to make it seem more dramatic. See also: any movie with a bomb counting down to zero.


While I've grown with people who spend their after-cinema time analyzing how realistic the film was, and do acknowledge it can be fun to some extent, it's just refitting the art into a whole another game and that's by definition completely unfair. It's like writing a car review of the new Toyota Yaris and complaining it doesn't handle well on a race track.

The art of cinema is to pull people inside in a story that is generally mostly fiction. It's like deception by definition: you only offer the viewer enough pieces of an alternate reality to help his imagination get started and do the rest. The point of that exercise is to tell a story, and pulling the viewer into the reality of the film is just a tool in presenting that story. There is no point making the film's reality more realistic other than to be able to suggest it to the majority of viewers as a plausible setting for the story.

The train scene is a typical timed action scene. It's enough to repeatedly show an increasing velocity reading, similarly to how you might show a countdown timer in a bomb-defusing scene. The point of flashing those gauges or numbers every now and then during the scene is to increase excitement and tension, which I'm sure the original author well understands. Assuming the movie is in wallclock time could turn out to be a fun exercise but in this case it did not because the timing analysis just ended up pointing out an irrelevant detail in the movie that was never even designed to be coherent. So, the discovery is not fun in itself, it doesn't add anything to the movie experience, and thus wouldn't really be worth much attention.


Is anyone really criticizing the movie for this? Did anyone really expect these minor details to be realistic and accurate?

I don't think anyone is upset over this. It's just a fun exercise.


Ah Toyota Yaris, the best and first car I ever drove. Probably because it was the first.


"So, the discovery is not fun in itself, it doesn't add anything to the movie experience, and thus wouldn't really be worth much attention."

Sorry Fun Police, but you don't get to decide what's fun for everyone. This wasn't a movie review, and if you're not interested in people enjoying trying to decide if a completely impossible concept (a car from 1985 traveling through time) would have worked within the reality constructed by the movie, then feel free to skip down to the next HN story.

Reading, then commenting on, a story which is self described to be on a topic you have no interest in, can be considered nothing more than trolling.


Actually, there is no way Sierra No. 3 could take a curve at 88 mph as shown. It's not a power problem. 19th century 4-6-0 designs are unbalanced and prone to derailment. There's a solution to that involving a complex suspension, but that came later.

More than you ever wanted to know about locomotive suspensions.[1]

[1] https://books.google.com/books?id=1A4iiGAz628C&pg=PA62#v=one...


This is a fun exercise, but...

> we assume events occur in real-time

this is completely unwarranted and invalidates the rest of the analysis.


I address this in answer to ant6n's comment.


...but considering that they only need to fall from an height of 258.88 feet to reach 88 miles per hours Marty most likely did made it to the future! Unfortunately he then died instantly by hitting the the bottom of the ravine once he arrived to 1985. :(


But because of the rotation of the Earth and in fact the whole Galaxy in the meantime, the vertical component of the ravine became the horizontal component of the road :)


If we assume time travel is possible which is quite a leap already, why do people fixate on things things having to keep their fixed point in space relative to... well.. relative to what? Frames of reference can really complicate this.

Perhaps time and gravity are related in a manner that means as an object travels through time it maintains position relative to gravitational influences (and local ones affect it far more than others due to the inverse-square relationship) and maybe the effect is strong enough on each part of the travelling body that it maintains orientation relative to those gravitation influences too (so the car not only stays on the road but conveniently wheels-down as well).


You only need to die instantly in that timeline.

1. Write yourself a note to keep a jerry can in the Delorean, put it on your person.

2. Set destination time back by a week.

3. Marty gets in Delorean and Doc pushes it off of cliff.

4. Next of kin and Marty read note given to them at the morgue.

5. Plot of BttF 3 evaporates.

Edit: This is too complicated. Just visit Western Union again and send a second letter about the jerry can.

Edit 2: Wait, there should be a 2nd Delorean in 1885 after Marty arrives. So Doc's Delorean should have some fuel unless Doc was joy-riding. I'm really not thinking 4th dimensionally.


Hadn't thought of that! And considering that based on what I calculated in the post he goes off the edge at about 70mph, he probably needs way less that 258 feet right?


The 70mph is horizontal velocity, gravity is vertical acceleration from 0. Total velocity is sqrt(sum of squares). It's unclear how much horizontal velocity the train would lose due to air resistance and due to the unclean launch from the ravine. (Would it fly off the end of the track, or tip off the end and tumble down?)


This analysis doesn't address the fact that the flux capacitor on board twisted the rules of physics locally :)


There is also no way he could have met himself in the future.

Edit: Unless the time machine was capable of visiting parallel universes.


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.


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.


> 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.

This is something I've mentally struggled with since the second film came out. His leaving 1985 temporally is an exit event; he ceases to exist in his own timeline. The only explanation I could come up with is that he does indeed visit an alternate timeline where Doc never created the time machine and therefore Marty never goes back in time to "fix" his father's resolve. There are hints about that; Old Marty is still unsure of himself and allows his boss to run all over him, his son took on his and his father's bad traits, etc. The only way this works is if Doc is unable to visit the same timeline going forward, and can only do so going backwards. The problem becomes, if every forward time travel event leads to an alternate timeline (as is necessary for existential reasons), and any changes made to his own past timeline also cause a new timeline to branch off, why is Doc so worried about fixing the past in order to fix the future? They aren't his past and future anymore, just ones he created by traveling through time in the first place.


"why is Doc so worried about fixing the past in order to fix the future? They aren't his past and future anymore, just ones he created by traveling through time in the first place."

Is it possible that an inventor brilliant enough to have built a time machine doesn't subscribe to the parallel-realities hypothesis, and is unaware of how his invention really works? We'd need to answer this question to get to why Doc Brown cares so much.


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.


>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.

They did that all after he got back. He left and returned at the same point, so from the perspective of an observer outside his timeline he was never actually gone.


> 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.


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).


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.


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.


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.


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.


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).


> it’s a shame Doc didn’t equip the Delorean with Tesla electric motors when he visited 2015. That would have made things easier considering the Delorean was equipped with a working Mr. Fusion generator in 1885

He put flying car parts into it. Why the hell would he want some lousy electric motors?


If the writers could actually see into the future they would have installed a LFTR mini thorium reactor instead of Mr Fusion(tm).


> He put flying car parts into it. Why the hell would he want some lousy electric motors?

I think the author is referring to the fact that then the Mr. Fusion could also have powered the vehicle while driving around on land. Perhaps flying would still be impossible without magical alternative-2015 fuel/parts, but at least you'd be mobile on land in almost any situation.


Was it working? I always thought Mr Fusion was damaged along with the time circuits when the Delorean was struck by lightning.


The Doc specifically mentions that Mr Fusion only powers the time circuits, not the rest of the car. So to get Back to the Present it would have had to have been functional, given the plutonium system was removed between BTTF1 and BTTF2.


Mr Fusion at least had to have been working. Otherwise in 1885 they wouldn't have been able to power the time circuits. That said, that doesn't mean the flying cart upgrades were still.


No, Mr Fusion is fine (hence no need to go trying to find ONE POINT TWENTY ONE JIGGAWATTS). The flying circuits were fried.


Enough all ready with this 88 mph requirement before the flux capacitor is activated. All they have to do is point the DeLorean east and the rotation of the earth will do the rest. Not to mention the earths orbital speed round the sun, the suns trajectory round the milky way and the milky ways trajectory in relation to the inertial reference frame, that's about 1.3 million miles per hour in the direction of Virgo.

Besides why didn't old-doc just post a letter to future-doc and get him to bury some plutonium in the desert in the past. Then old doc goes and collects the plutonium and goes-back-to-the-future and collects the letter and goes back to 1785 and burys some plutonium in the desert, then goes-back-to-the future .. my brain hurts ...


Well, relativity tells us there are no preferred reference frames. But I believe relativity also tells us that time travel is not possible.


There are more plausible depictions of travelling through time out there than using a DeLorean travelling at 88 mph. Take Primer for instance:

"Primer (2004)" http://www.imdb.com/title/tt0390384/




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