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    Date Display 

  • The date indicator on the time machine only has room for four numbers for the year. So what if you wanted to go back to say, see the dinosaurs (i.e at least 65 million B.C) you just can't go back before 0 A.D?
    • Scrolling displays have existed for a while.
    • The DeLorean we see is largely a prototype. Doc was more interested in making sure it worked than before addressing UI issues like these. Computer displays of the 1980s were bulky (CRT) and/or expensive (monochrome LCD) to fit into a cramped interior like the DeLorean's; so Doc would probably be better off travelling to the future to get a fancy screen regardless.
    • Also quite possible the time machine can't go back that far anyway. It might have an upper limit, though admittedly it didn't in the cartoon (where the display was also longer).
    • In a Back to the Future fanfic where Doc's kids go back 65-million years, one of his sons hooks up a special display to the time circuits to properly display that year only for Doc to later explain that it wasn't necessary, you just needed to enter the correct year, it simply wouldn't be properly displayed.
    • Maybe there really wasn't anything before 0000, and the birth of Christ is a thing that happened in this universe as Doc stated.

  • So what would happen if you went to 11:59 p.m. on December 31, 9999 and waited one minute?
    • The Y 10 K bug strands you in a post-apocalyptic wasteland...obviously.
    • Or, integer overflow causes it to roll back to Jan 1, 0000.
    • Just because it's possible to display times up to 9999 AD doesn't mean it's able to handle dates that far, so it might conk out long before (Truth in Television - some older computer systems would break by Jan 19, 2038). If it can though, assuming it stores time in minutes since 0000-01-01 00:00, you'd need at least 33 bits to store the value which would actually cover you until approximately the beginning of April 16332. If it's stored as the number of seconds since 0000-01-01 00:00, you'd need at least a 39-bit unsigned integer, which would cover you until roughly mid-January 17421.
    • Assuming the Delorean can travel that far into the future, you would arrive the year 9999 on December 31 at 11:59 and... that would be that. The date display records the time you're travelling to, but it doesn't continue ticking over once you've arrived. It just means that it would be difficult to set the Delorean to travel at any point further than that.
    • What would the present time readout display in this scenario?

    Doc being awfully shut-mouth 

  • How come Marty and Doc are okay with Doc bending the rules and wearing a bullet proof vest to avoid being killed, but Doc flat-out refuses to tell Marty about the accident that'll break his hand? Admittedly, the message is stronger knowing that Marty made the right choice of his own accord, but it does make one wonder why Marty didn't call the Doc out for being hypocritical - the guy was willing to bend the rules to save his own life, and even help his kids from going down a dark path.
    • If Doc hadn't worn the bulletproof vest, he would have died. While Marty knackering his hand and ending up a loser is unfortunate, it's not exactly life-threatening. Plus, Doc only ended up being willing to bend the rules and wear the bulletproof vest because Marty was insistent.
      • Given Marty's an aspiring musician though, breaking his hand seems pretty life-altering.
    • Doc's always been careful about giving away info about the future, it's Marty who isn't concerned about it. Who knows, maybe in the original timeline Marty broke his hand and later on found out Doc knew, giving him a big chewing out, but we never see it because it happened off-camera.

    Why does everyone dislike Doc? 

  • As we learn in the second film, Doc Brown is a good enough scientist that he received an award for his work before the events of the first movie (chronicled in the local paper, no less).
    • The only people who outright call Doc crazy are Strickland and Old Biff, who are both jerks, and the former probably has impossibly high standards. It's possible that most of the town may view Doc as eccentric but harmless. He does seem to have his own business and can afford to have a truck associated with said business.

    Marty's ancestors 

  • How come Marty doesn't have any ancestors who look like George, Dave or Linda?
    • He probably did, but we just didn't happen to meet them over the movies.
    • How come Seamus, Marty Jr., Marty's daughter and William McFly (as seen in the old photograph in the library) all look like Marty, yet George, Dave, and Linda look nothing like any of them?
      • Recessive/dormant genes?
      • The Telltale game has Artie McFly, Marty's grandfather/George's father, look and sound roughly like Crispin Glover.
      • Maybe Arthur McFly took more after his mother (let's call her Miss Jones) than his father William McFly. George takes after his father and looks more like a Jones than a McFly. Dave and Linda take after their father, still with the Jones look. Yet the "recessive" McFly genes reappear with Marty.

    Marty's friendship with Doc 

  • Do Marty's parents even know he and Doc Brown are friends? There are a few close calls here and there (notably at the end of the first movie/beginning of the second), but they never see the two of them together that we're aware of, not counting when 1955 Lorraine follows Marty to Doc's house to ask him to the dance. The only adult who makes any mention of their being friends is Principal Strickland.
    • Most likely yes. Word of God says that Marty has been friends with the Doc for 3-4 years by the events of the film, and he actually had a part-time job as the Doc's lab assistant. Unless George and Lorraine are REALLY that neglectful towards their children, they had to know.
    • It's understandable if Lorraine in the original timeline disliked Doc, seeing how she seemed to be a judgmental type. More likely, Lorraine of the newer timeline was accepting of him, especially if she remembers him supposedly being the uncle of "Calvin Klein".
    • The spin off material confirms that they know. As for the movies, the various 1985 versions of George and Lorraine each only appear for a few minutes each and there's no real reason for Doc to come up in conversation then.

    Plutonium 

  • If Plutonium/Mr. Fusion is only used to power the actual time travel components of the DeLorean, why did it keep shorting out during the first movie?
    • Truth in Television. One of the main reasons why DeLoreans were unsuccessful as cars was that they had incredibly unreliable ignition.
  • For that matter, why is plutonium/Mr. Fusion stated to only power the time travel in the third movie, when Doc specifically says in the first that the car itself is electric?
    • No, he says that the time travel circuits are electric, but need such a huge electric charge that plutonium is the only way to generate it. The car itself is gas-powered, otherwise Marty shouldn't have been able to drive around in 1955.
      • With the time travel taking a whopping 1.21GW though, there should be plenty of juice to drive even if there isn't enough for time travel. It's not even like Marty drove it a lot; it died shortly after he arrives and from then on it's either being towed or pushed around, the next time it actually drives is during the lightning sequence.
      • The car itself doesn't use the electricity generated by the reactor. At all. This is a major plot point in the third film. Even if there is surplus electricity, the car can't use it because it has a gas-powered motor rather than an electric motor.

    Spacetime 

  • The DeLorean obviously travels through time, but how does it also travel through space? Consider this: the Earth is tearing through space at fantastic speeds. Even when Doc sent Einstein on a just one-minute trip, the Earth still will have moved quite a bit. If Einstein's coordinates only move through time, and not space, shouldn't he pop out in outer space, where the Earth was one minute ago?
    • Perhaps the Flux Capacitor locks itself onto a gravity well.
    • There are no absolute coordinates in the universe anyway. If it stayed in place, it would have to be in relationship to some other object. Might as well make that object the earth.
    • It's less of teleportation-styled time travel and more of wormholes or portals through time. Essentially, the DeLorean opens wormholes from one location to the next.

     88 MPH requirements 

  • So, does the DeLorean need to be going at 88 MPH or does it just need to achieve that speed? Put another way, if you were going at 89 MPH and you turned on the time circuits, would you go back in time or would have to drop down to 88? What about flying? Is 88 miles per hour the ground or air speed? What about flying against (or with) the wind?
    • Obviously the DeLorean has to be moving forward at 88 mph, not just spinning its wheels, or Doc could just jack the back of the car off the ground and gun the engine until the time circuits kicked in.

  • Also, why has it to be 88 MPH anyway? Is it just an arbitrary setting by the Doc? If so, he probably could have changed it when they were stranded in 1885 to a lower speed, perhaps the speed they could reach and maintain using the horses... So this can't be it...
    • Probably has something to do with how the Flux Capacitor works. Chalk it up to some weird law of science, like the speeds of light and sound.
    • Perhaps Doc picked this number to avoid having accidental activation of the time machine. 88 is faster than highway and residential speeds, so if Doc is driving the DeLorean somewhere and accidentally turns it on (or it malfunctions or something), he doesn't risk zipping off to the crucifixion in the middle of I-90. After all, both Marty (when being chased by Libyans) and Doc (when trying to land after destroying the Almanac) did exactly that; it was just unfortunate both times they also happened to reach 88
    • Since "flux capacitor" is a mishmash of electromagnetic terms, and Doc said that the DeLorean's steel frame is important, the 88MPH requirement is probably to create a powerful electromagnetic field to trigger the time jump. A moving electric charge creates a magnetic field and vice versa, so Doc's apparently either charging or magnetizing the DeLorean's exterior, and then speeding the car up to generate a strong enough EM field.
    • It's a little joke by Doc Brown. To travel through time, you must (on Einsteinian theory) exceed light-speed. Exceeding light-speed in theory means your mass goes beyond infinity, yes? Which is unbelievable on its own, but you must then somehow catch up and reassemble the infinite number of photons that have spun out since the moment you want to go back to. That would be a task in the order of double infinity, yes? Thus, 88.
    • Consider those crazy sparks that appear in front of the DeLorean as it accelerates. The flux capacitor might be creating waves of wormhole portal energy that travel at 88, which is why the DeLorean also has to be traveling at 88mph - so it can actually pass through the wormhole and time travel.
    • Word of God is that there is absolutely no deep meaning behind it - it's just an easy-to-remember number that sounds impressive..

    The De Lorean's flight capabilities 

  • What actually powers the flying ability of the DeLorean? The Time Circuits & Flux Capacitor were powered by Mr Fusion & the Internal Combustion Engine was run on Gasoline, what was the Hover ability run on?
    • The most likely explanation is also the internal combustion engine. Mr Fusion was, after all, a non-standard mod added by Doc.

    Why is the De Lorean still gas powered? 

  • So Doc (sensibly) stuck with a gas engine in 1985 because the nuclear reactor is carefully matched to the time circuits and it's impractical to power the motive capabilities of the car from plutonium as well. But why does this persist after he's had the car flight-converted and Mr-Fusioned? He now has a reactor that can effortlessly power everything in the car with a few banana peels, why not make the drivetrain electric as well and get rid of a potential problem?
    • To be fair, it's not exactly a problem that one would foresee cropping up. Going by that logic Doc would need to replace the tires with something else too, in case they get popped or something, but he also didn't do that, since the chances are low and Doc presumed he should be able to get a replacement easily enough. One can't prepare for every contingency.
    • It's also a prototype. It was meant to be as much a proof-of-concept as a time machine. The movie's commentary describes the car's look as "dangerous" with parts hanging off of it. Had Doc been planning for much longer trips, he'd use a different vehicle and plan for other contingencies. He simply didn't build another time machine until circumstances required it. Besides, the time periods he was visiting had gasoline and usable parts available.

    Doc, go back and fix all this! 

  • So on Doc's "personal timeline" he ends up with a time train and pretty much full knowledge of the events of the movies. Why not just use the train to go back and let himself know at various parts what he has to do to ensure the "ideal" future?
    • Why would he want to do that? Everything worked out perfectly in the end. Why would he want to risk messing that up?
      • Because he already did it at least once: he heeded Marty's letter warning him of his own death, and took steps to prevent it, way back in the first movie:
        Marty: What about all that talk — about screwing up future events, the space-time continuum?
        Doc: Well, I figured, what the hell.
      • But in that case he actually had something to prevent, namely his own death. As of the end of Part III, what would he want to prevent? George's success? Biff's comeuppance? Marty avoiding the auto accident? Not really. He wouldn't change anything because there's nothing to change. Everything is already perfect.
    • For this to work, the Doc would have to travel through time talking to other versions of himself. In II he makes it quite clear that he and Marty should not be interacting with their older selves, and goes to great lengths to avoid his older self seeing his face in the Square. Also, doing all this could have created a paradox where he never ends up in 1885, and thus never gets the chance to create the train time machine.

    The flying De Lorean's controls 

  • How on earth does Doc control his height and altitude in the hover-converted DeLorean? Surely we should see him doing more than merely turning the steering wheel—that should only turn him left or right. Shouldn't there be an extra lever or something somewhere?
    • Maybe by additional foot pedals?
    • Or pressure pads in the steering wheel that act sort of like a non-obtrusive version of the wing-flap controls on a model plane remote control?
    • Maybe you just push and pull on the steering wheel the same you do on a plane's yoke.

    Doc and Marty becoming acquainted 

  • How in the world would have Doc and Marty known one another in the first place? They are not exactly what one would call similar. One is a Musician, the other is an Eccentric Scientist.
    • Word of God is right here. Turns out that Marty was just a curious kid circa 1981, and wanted to see this crazy inventor who everyone told him to avoid. Doc found Marty's curiosity to be heartwarming, and hired the lad on as a part-time lab assistant. The filmmakers cut this because they had a lot of exposition to get through and didn't think that bit of information was especially important. And they reasoned that kids are naturally drawn to eccentric people anyway.
    • Doc having a super awesome human-sized guitar amplifier at his place provides a plausible reason for a wannabe rock god like Marty to befriend him.
    • The comic book series features an origin story. The Readers' Digest version: in 1982, Needles broke the vacuum tube from Marty's guitar amplifier, and Marty went looking for a new one, only to find the music store had just sold their entire stock to Doc, whom he knew by reputation only at the time. Doc had a series of puzzles that allowed access to his lab for anyone who could solve them, and Marty was the first one who could, so he offered him a job. As for the tubes, he just needed the box they came in because it was the right size for one of his experiments.

     DeLorean covered with ice after traveling through time 

  • When the DeLorean finishes a jump through time, it emerges freezing cold (Doc even visibly recoils in pain when touching the door to open it, because it's so cold). Where does the ice come from? The ice is just frozen moisture, but it emerges from time travel covered with ice. If time travel is instantaneous, how does it have time (no pun intended) for it to get that cold and accumulate so much ice? The ice doesn't form on it after arriving because the car is so cold, it's already there. What's happening to the DeLorean during the time jump, and what kind of atmosphere or dimension is it traveling through, where it gets so cold and there's so much moisture that it emerges covered in ice? Is time travel truly instantaneous, or does it only seem instantaneous from the point of view of the passengers? Also, when Doc emerges from the future to warn Marty and Jennifer about their kids, the DeLorean is not covered in ice and isn't so cold that Doc can't touch it, as he touches it several times with no reaction when dumping stuff in Mr. Fusion for fuel. Does the DeLorean only go through a region of intense cold when traveling forward in time, but not backwards?
    • As to why it's covered in ice at all, the pilot episode of Stargate SG-1 may actually answer that. After a journey through the Star Gate, people come out covered in a thin layer of frost, much like the DeLorean. The reasoning she gives is that it's the result of the compression the molecules undergo during the millisecond required for reconstitution. As for the other, when Marty first arrived in 1955 and crashed in to the barn, the car was indeed covered in a thin layer of frost (which quickly evaporated and melted in to water droplets). Upon his return to 1985, you can clearly see ice on the car. When Doc meets Marty and Jennifer at the end of the film, there is a bit of frost on the front of the car.

     What would happen if the DeLorean didn't slow down and had enough fuel for multiple trips 
  • If the driver didn't slow down from 88 miles per hour upon arriving at the destination and had more fuel then he needed, would the DeLorean keep going back in time a few seconds and would an external observer see several DeLoreans appear in a line for a sit second after the Delayed Ripple Effect had finished its work?
    • For the most part, every time the DeLorean makes 'the jump', it appears the driver (usually Marty) either hits the brakes, or eases up on the gas pedal. Part of the Flux Capacitor's name includes the word "capacitor", since it appears the car needs to be at 88 for several second before it jumps, it would take several seconds after the jump before it could again.
    • No doubt, besides the hardware, there's likely software that would only allow for one jump at a time. It's plausible that once the car completes a jump, it won't activate the flux capacitor again until a new destination is entered, there's fuel for the reactor, and you accelerate to 88.

     He'd tear through us like we were tin foil 
  • In Part II, Doc tells Marty that they can't land on Biff's car because the Delorean is too fragile (Truth in Television as the stainless steel construction was extremely brittle). How is it, then, that in the first movie, it survives head-on collisions with a scarecrow, barn door, bale of hay, a pine tree, a movie theater door, and a garbage can without taking any damage?
    • The DeLorean isn't actually made of stainless steel, it's stainless steel body panels attached to a fiberglass tub with a backbone steel chassis that holds the running gear and suspension. Landing on top of any car would've caused serious damage, ripping through critical systems like tinfoil, causing a crash and making the DeLorean un-drive-able. In any case, the car isn't a tank.
    • As to how it survives head-on collisions with various objects without sustaining damage? Part of it can be attributed to movie magic with one exception: the pine tree. After arriving in 1955, the car failed to start after running over the pine tree. It's possible that something got snagged underneath and caused starter issues, was not properly repaired and led to intermittent problems that were later corrected in 1985.

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