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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 Televsion - 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?

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    Wrecking the Car 

  • In the altered 1985 McFly household why does everybody freak out - notably Dave ("why wasn't I informed?!") - when Marty inaccurately notes that Biff wrecked THE car as if that would leave the whole family stranded? Marty certainly has his own super-cool ride as it turns out. Shouldn't Dave the businessman (who still lives at home) at least have his as well?
    • They're less worried about being stranded and more freaking out that there was a major accident with their property that nobody told them about.
    • It's also plausible that they were alarmed by Marty's story because they're finding out about this alleged vehicular damage from Marty. From their perspective, it makes it sound like the kid might've taken his parents' car without permission and totaled it, so they're freaking out that Marty A) might've done that, and B) if he had, could've gotten himself killed in the crash.

    Hooking up the camcorder 

  • How does Marty take a 1985 camcorder and hook it up to a 1955 TV system? Even if Marty brought cables, it's unlikely that TVs of that era had any inputs (besides the antenna). The Doc doesn't look like a A/V expert. The only way he could do that if he took apart the TV and used a soldering iron. What gives?
    • Bit of Reality Is Unrealistic - 1980s camcorders are largely backwards compatible with 1950s TV sets; this was specifically mandated when the US started adopting color TV. In fact, connecting to old 1950s set would be a lot easier to do that to than a modern one as the connection would be physical wires instead of circuit boards, so it's simply a matter of bridging them.
    • Don't forget, Doc's a Mad Scientist. If he can make a time machine, he can get a camera to work on a TV set.
    • An earlier version of the screenplay had Marty as an A/V whiz of sorts, so maybe it's a hidden talent of Marty's that the filmmakers didn't really expand on in the films proper.
    • Possibly Doc had previously modified that TV as part of one of his non-time-travel-related experiments?

    Marty visiting Doc 

  • What the heck was Marty doing going over to Doc's garage at the beginning of the film, anyway? He can't possibly blame the fact that he was late for school on Doc's clocks — he was only there for a few minutes, and he was wearing a wristwatch.
    • He probably went by to use the speaker since Doc had said he'd be out, and spent more time there than we actually saw, maybe straightening things up and getting ready a bit, and didn't think to look at his wristwatch because he was surrounded by clocks that all said the same thing.
    • Marty also shakes his wrist on a few occasions after looking at his watch, implying it works poorly.
    • Alternatively, he looked at his watch, saw he had some time to waste before going to school, did so, and (upon seeing all the clocks in Doc's garage) thought his watch had gone bust and he had more time than he originally thought.

    Just tell him! 

  • The first couple times Marty tries to tell Doc about the future (and the fact that he'll get shot), one thinks he ought to have been far more assertive.
    • Doc's just as stubborn and assertive about not wanting to listen. Marty did eventually try at the climax, but they got distracted because Doc had to hook the cable back to the clock tower. Plus, it's kind of a hard thing to broach with someone, especially a close friend — "Hey, you're gonna be gunned down in thirty years, I know because I was watching!"

    Car keys 

  • Who the hell keeps their car keys in the trunk?!
    • Most likely, one of Biff's helpers must have swiped the keys from the top of the car and threw them in the trunk so no one could get him out.
    • Or maybe the band member who owns the car just set them down by accident in there and forgot to pick them back up.
    • Or the keys were sitting on the bumper, laid there absentmindedly and they got knocked in when Marty was thrown into the trunk.
    • Older cars had trunks that had to be manually locked, and the car's owner didn't.

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    Cutting it a bit close there, Marty? 

  • Marty could have traveled to any point in 1985. Why choose a point that was only eleven minutes before Doc got shot?! That wouldn't exactly be enough time to do anything about it even if he got there. Why not a day? When he got to 1985, he could have called Doc and told him.
    • Maybe some of that paradox talk actually seeped through and Marty was trying to minimize interference in events 'he' was involved in. Or maybe he was just in panic mode and went with the first idea that came to him. After all there was a lot going on at the moment.
    • Had the DeLorean not broken down, it would be more than enough time to get to the mall, and pick up the Doc before the terrorists arrived. It would probably cause a huge paradox, as it would keep himself from traveling back in time, but that's probably what he planned on doing.
    • Plus he isn't very good at thinking fourth-dimensionally.

    Just a vest? 

  • When Doc taped up the letter and found out what Marty had been trying to tell him all this time, why was a bulletproof vest his only precaution? A bulletproof vest in and of itself isn't going to protect you from more than a pistol, and it definitely won't protect you from getting shot in the head, so he's damn lucky that didn't happen. Why not get a gun or something?
    • He had a gun, but it jammed and he threw it away. Doc probably chose a vest because he calculated it gave him the best chances of survival without tipping Marty off to its presence and thus causing a paradox.
    • Doc might also have reinforced the vest.
    • As for the reason why they don't shoot him in the head: Most gunmen are trained to aim for the center of mass as it's the best chance for actually hitting something, let alone someplace vital. The guns they're using aren't too terribly accurate in the first place and a headshot, even at relatively close range, would be hard to make.
      • They may not have been aiming for his head, but there's still a chance they could have hit him there anyway, or his neck, or his arms and legs. Marty's note just said Doc would be "shot by terrorists"; he didn't specify where.
      • That's from a perspective of someone who's trying to survive. Doc, as a scientist, seems more concerned about not destorying the universe via paradoxes, so his train of thought is roughly "Well, this is the best I could do. If it still fails, I hope Marty takes good care of Einstein".
      • That white jumpsuit Doc wears over the vest probably makes his torso a very inviting target, too.
    • He probably went with the vest so that it would look like he was killed so that when Marty went back, he would still think that he was killed and warn his younger self.
      • Couldn't he just feign collapsing, though?

  • Did bulletproof vests that could protect you from several 7.62 rounds fired at relatively close range, exist in the 80s? I've been investigating a bit, and the standard issue back then in the US military was the PASGT vest, which was only Level II (meaning it could stop most handgun rounds, but not rifle rounds), and even modern day armor will only save you from an AK if you are wearing ballistic inserts underneath the vest.
    • General consensus is that Doc Mad Scienced the vest to beef it up.

    What happened to the Libyans? 

  • As Cracked.com pointed out, after crashing into the photo booth, the Libyan terrorists are still there, but we don't hear from them for the rest of the movie — or the rest of the trilogy, for that matter. What's up with that?
    • The crash likely killed them - remember they were traveling close to 88MPH, and the photo booth was already on fire from the DeLorean's time jump, so even if they were just knocked out, they probably burned to death soon after.

    Crossing the wire 

  • How in the world did Marty manage to cross the wire at exactly the right second? Especially considering the problems with the car's ignition? Talk about catching a lucky break.
    • Fridge Brilliance. Lightning takes the path of least resistance; the differential charge had been building up for a while, and the sudden contact between wire and hook created a better conduit for the electrical discharge than the clock tower alone, so instead of going to the clock tower an unknown number of seconds after the clock hands shifted, it took this path of least resistance immediately. Doc's rig didn't just intercept the lightning bolt, it attracted it.
    • It doesn't need to be the same exact moment, anyway; as long as Marty was going >88MPH, the time travel should kick in.

    Marty tearing a page out a phone book 

  • What was with Marty tearing a whole page out of a phone book just to get one number? And why was the café owner so blasé about it?
    • It's a page from a phone book. Phone books were and are replaced with relative frequency and not exactly rare or difficult to acquire; in fact, it was probably given to the café for free from whoever phone company they were subscribed to.
    • The owner isn't blasé. He's actually pissed. When Marty first walks in, the owner is neutral. Once he sees that Marty has torn a page out of the book, he responds with an annoyed "Are you gonna order something?". The implication is that Marty had better do something to make up for the phone book he just ripped.
      • The owner's "Are you gonna order something?" seems more because he thinks Marty is a mooch/timewaster.
    • Marty rips the whole page because he had no pen available to take notes, and it'd be messy if he tried to tear only the part he wanted out.

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    Doc's fine after being struck by lightning 

  • How did that bolt of lightning not kill Doc, gloves or no gloves? Not only did he survive, he practically no-sold it — he simply fell to the ground and got back up after a few seconds.
    • Because the bolt of lightning didn't go through him. Electricity is going to take the path of least resistance, and human bodies are actually pretty resistant. Given the options of going through a human body and through a metal cable explicitly designed and made to move electricity, electricity is going to go through the cable.
      • That's inaccurate. Electricity takes all paths, the available current being divided between the paths, inversely proportional to the relative resistance of each. (e.g. if one path is 50 ohms and the other path 100, then the 50 ohm path gets twice the current of the 100 ohm path.) So even though the cable provided a nice low impedance path to ground, One'd expect some of the current to go through Doc.
    That said, a lot of the people are struck by lightning every year survive. It's a hella lot of current, but it's also very very brief. They aren't necessarily just fine, though. Mental problems are not uncommon in lightning strike victims.
    • Doc knew he'd be clambering around on a rooftop in a lightning storm, and he had no guarantees that the tower wouldn't be struck again after the first discharge. He probably wore rubber-soled boots, rubber gloves under his work gloves, and whatever else he could find as insulation.

    Doc wrecking the plaza 

  • Doc's tinkering with cables in the center of town, a policeman explicitly sees him, then a lightning bolt destroys the clock tower and sets fire to the road. How does he not end up in trouble over this? How can he justify it? "Weather experiment" doesn't quite cut it anymore after the strike happens.
    • In a deleted scene, Doc bribes the cop with $50 and the officer says "You're not going to set anything on fire this time, are ya Doc?", indicating Doc's done stuff like this before. As for the fire trails, they disappear within a minute as evidenced by the end of BTTF2 and beginning of BTTF3.
    • Well, Doc can't be blamed for the existence of bolts of lighting, can he? He can simply say that it was an unexpected disaster.

    Going to 2015 instead of 2010 

  • What made Doc change his mind and go to 2015 instead of 2010?
    • He says right then and there that he changed his mind because he felt 30 years was a nice round number.
    • Doc wanted 25 years in the future before Marty went (30 years) through time and changed history, sharing a big adventure together. Upon seeing the "current" Marty and taking him home he was possibly inspired to have his own 30 year future jump.
    • In the original screenplay, the present was 1980 but Marty still went back to 1955, not 1950 - i.e. only 25 years back. Doc's mention of seeing who wins the next 25 World Series is a remnant of that; at that point, the time travel was in increments of 25 years rather than 30. By the time the movie was made, that one line hadn't been changed, and by that time, 25 years in the future = 2010.

    George allowing Biff to stick around 

  • Why would George want Biff anywhere near his wife and kids? He was a breath away from raping Lorraine the night of the dance. Even ignoring that he's still an asshole who is still physically stronger than him. He could come back anytime and get revenge.
    • Combination of time and Values Dissonance. Attempted Rape (and even "successful" rape) wasn't as big a deal even in the 1980s (let alone the 1950s) as it is today. George and Lorraine, of the 50's upbringing, just chalked it up to "youthful high spirits" and "drunken indiscretion" and didn't really poke at it any more than that; add on three decades and they might've forgiven him.
    • Plus, sometimes you simply can't get rid of the bad people in your life, if you live in a small community.
    • Alternatively, George keeps Biff around because he's a living trophy, evidence of that time he bravely took down the school bully and had his life changed. As for why Biff doesn't try to 'get revenge', even a complete dumbass like him will be aware that, as George is his superior, he's in no position to try anything funny.
    • In the comic series, there's a scene that takes place only days after the attempted rape where Lorraine reaches out to Biff to console him for the loss of his grandmother. This of course muddies the waters even further: she couldn't have forgotten that quickly what he'd done!
      • You don't have to forget to forgive, or even to forgive to be compassionate. Rubbing salt in the wound might have been satisfying, but Lorraine is a better person than that.

    The letter 

  • In the end of the movie after Doc survives being shot at, he hands Marty's warning note to him and explains that "Well I figured...what the hell?" Ok, so he had that thought and then what? He'd torn up the letter and thrown it way, so how did he get it back?
    • "Common Knowledge". Doc never actually threw it away. He rips up the letter, then covers his ears when Marty starts to tell him about the Libyans. When the tree branch falls and disconnects the wire, Doc yells, "Great Scott!" Doc looks down at the fallen wire, up at the clocktower, and then (quickly) stuffs the letter fragments into his coat pocket right before he runs over to grab some rope. It's a quick sleight of hand, and you need to have a good eye to see it, but it's definitely there.

    Digital watch 

  • When Marty first enters the 1955 diner in the first film, his digital watch starts beeping and he has to hide it from Lou. So why doesn't he show it to Doc when Doc doesn't believe he's from the future? Doc can dismiss funny clothes, the picture of Marty's family, and Ronald Reagan as the President, but a high tech future watch would be pretty impressive.
    • On rewatch it appears that Marty doesn't have his watch on him when trying to convince the Doc he's from the future.
      • But he had it in the diner (he had to hide it from Lou when it beeped), so that means he must have lost it somewhere in town (maybe Lorraine took it off him).
      • Marty probably took it off after the beeping incident and shoved it in his pocket, forgetting about it when he was trying to prove himself to Doc.

    Marty already seems not to be like father like son? 

  • The Marty we see at the beginning of the first film is vastly cooler than anyone else in his family and probably among the top 5% cool kids at school. He plays guitar, fronts a rock band, is an expert skateboarder, is dating someone who looks like Claudia Wells, and all the girls in the aerobics studio wave to him too. Now the running gag through all of the films is that everyone is like their parents and their parents are like their parents, but George and Lorraine are complete losers. How'd Marty-1 escape his destiny, even before he changed his past?
    • Remember Lorraine was a cool and popular girl in high school; she only became a loser after marrying George. And as we see in Part II, Marty's life, even after fixing his family, follows the same path.
    • The thing he inherited from his father was his lack of drive and refusal to fight for what he thinks is important. Both he and his father are interested in creative works, but refuse to send their work out to companies out of a fear of rejection. As a result, Marty in the original timeline is implied to end up like his dad and take the route of least resistance, working a desk job or something instead of doing what he really wants. This was a point in the second and third films: Marty's Berserk Button is calling him a coward or chicken. Someone does this and it blows his future.

    Shifting gears 

  • How does Doc shift gears when the DeLorean is under RC control? While automatic was an option on the DeLorean, it's fairly well established that the one used for the time machine has a manual transmission since Marty shifts into 5th gear just before going back to 1955.
    • Close-ups of the shifter show it surrounded by wires. Doc probably rigged it and the clutch with small servos to do the shifting via remote.

    Everyone's different except Marty 

  • How come Marty altering the events of 1955 changed the lives all the other members of his family, but not his? His brother and sister are very different from the ones in the original timeline, but Marty still has the same room, wears the same type of clothes (if he wouldn't, his family members should be surprised of his clothes, just like he was of his brother's fancy suit), dates the same girl, etc. All that changed for him, apparently, was that he got a cool car.
    • There's a theory that something did change for him. Notice how the "Don't call me chicken" Berserk Button doesn't exist in the first film, but is prominent in the second and third. The theory goes that growing up with an assertive father figure made it such that Marty felt he had to prove himself in ways he didn't when he had a pushover for a father.
      • There's not any real evidence in the movies that changing the past changes the personality of a time traveller when he returns to the altered future, it's only the setting of his life that has changed. Regardless of how the past is changed, Marty and Doc remain the same as they were in the beginning of the first movie. It's true that the "chicken" Berserk Button doesn't seem to appear until the second movie, but on the other hand no one in the first movie calls Marty "chicken" or anything similar, so it's perfectly possible the button was always there.
    • Marty's young, and seems to be the most independent-minded of the family. He's apparently always sort of done his own thing, so it's not too surprising he changes the least from bettered circumstances. To judge from the car the major difference is that his parents seem to appreciate his personality and are willing to reward it and encourage him. In the original timeline Marty was independent and outgoing in spite of his father, in the new timeline he's probably that way because of his father.

    Back at the Mall - now what? 

  • When Marty goes back to 1985, what was he exactly gonna do to save Doc cause he probably assumes Doc didn't read the warning letter in 1955? The DeLorean stops and he sees the Libyans drive by and he tries to run after them. But if the DeLorean didn't stop and he made it in time to Doc before the Libyans came, what would he do cause we clearly see the other Marty is there with Doc?
    • He would have gone to the mall as fast as he could, and screamed "The Libyans are coming!" so that Doc and his former self would flee. Of course, this would create a paradox. But Marty isn't really thinking about that.

    Lightning strike time 

  • The whole plan in the first movie is based on the fact that they know the exact moment lightning strikes the clock. One problem with that: the clock is two-handed and therefore cannot show seconds. The lightning could strike at 10:04:05, or 10:04:17, or 10:04:58, but they act like it will definitely happen at 10:04:00.
    • Just because the clock doesn't have a second hand doesn't mean that someone couldn't figure out from the internal mechanisms when it stopped.
    • When Doc is reading the flyer out loud for the first time, he mentions that lightning will strike the clock tower at "precisely" 10:04 PM. This means right when the clock changes over. How he / anyone knew that is another question.
      • It's possible the person who wrote the article determined the exact time by examining where the clock's gears stopped.
    • Furthermore, even if it's exactly 10:04:00.00000000 down to Planck time, leap seconds have been added to account for irregularities in Earth's orbit ever since 1972. Does the DeLorean account for any intermediate leap-seconds between the origin and destination time-frame? Can it extrapolate for times before 1972 or likely leap-seconds in the future? Will Doc go to the end of time and get the definitive list of leap-seconds, leap-days, and other timekeeping aberrations for all of history?
    • The exact second doesn't matter. Marty (or indeed any human) won't be able to drive accurately enough, and even if they knew the exact supposed second by the clock's third hand it might not be accurate (the clock could still move a couple of more seconds after the strike or be delayed, etc). The best they can do is hope that between the moment the lighting strikes and the moment the car touches the cable the electric current is still running through the cable, for which they have several seconds, maybe a whole minute. Thus they calculate that the car will touch the cable in the same minute the lighting strikes and hope for the best.
    • A headscratcher above suggested it's a reverse cause-and-effect thing: the DeLorean contacting the cable allowed the lightning to flow and thus, it did. In the original timeline, the bolt might very well have occured in a different second.
    • Doc could also have installed some capacitors to accomodate.

    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.
    • Who says that Doc ever actually knew that future-Marty's misfortunes specifically stemmed from a broken hand suffered in 1985? Jennifer only found out because the police dropped her off at the McFly house to eavesdrop. All we know for sure is that Doc knew Marty's kids got themselves arrested in 2015. He could've read about it in the USA Today while waiting for the DeLorean's flight conversion to be completed at the garage.
      • In Part III, Doc specifically says "Marty, you can't go losing your judgment every time someone calls you a name! That's exactly what causes you to get into that accident in the future." This shows that he does know about it.

    Future money 

  • In the diner in 1955, Marty asks the guy behind the counter for something without sugar in it, to which the guy responds by giving him a cup of coffee. Marty then pays for the coffee with the loose change in his pocket, which came from 1985. Wouldn't the guy behind the counter have noticed something funny about that money? In 1955, dimes and quarters were made out of silver, not a nickel-copper sandwich like they were in 1985, and the two metals don't look the same. The proprietor should have suspected him of trying to pass off cheap counterfeit slugs.
    • They might be made from different metals, but they look the same and pass a casual scrutiny, which most who aren't coin collectors would do.
    • It could also be that, by the luck of the draw, Marty happened to have been carrying change that came from 1955 or earlier.
    • The novelization specifies that the cost of the coffee was five cents. Nickels were made from the same material in 1955 as in 1985. So unless Lou looked at the date (and he clearly doesn't), there's no reason for him to be suspicious about it.
    • This scene did in fact happen in the first draft of the script, with Marty being thrown out of the cafe for trying to pay with 'counterfeit' money, at which point he saw George being hassled by Biff.

    How far is the Mall from Hill Valley? 

  • Twin Pines Ranch is where the Twin (Lone) Pines Mall is in 1985. When Marty crashes in 1955 he drives long enough to escape Peabody and until the sun rises, and still has to walk a mile or two to downtown Hill Valley (as the sign indicates), but when he returns to 1985, he spies the terrorists rounding the corner and is forced to pursue them on foot. Not only does he get back not too long after the terrorists gun down Doc, but he managed to cover >2 miles or so in less than ten minutes?
    • This is assuming the mall/farm is farther from town than Lyon Estates. But if Marty was initially heading home, he might not have been heading towards town after leaving the farm.
    • Sunrise wasn't actually that far off. The destination time on the time circuits said 6 AM, and sunrise was about 15~20 minutes after in CA on Nov 5, 1955.
    • To run two miles in ten minutes, you'd be running at 12mph. Google says the average human running speed is 10-15mph, so what Marty does isn't implausible at all, especially for a young man in good shape and, as mentioned below, a big motivation to keep his adrenaline flowing.

    Biff breaking George's arm? 

  • What would have happened if Biff was successful in breaking George's arm?
    • He probably would have trouble standing up to Biff from then, Lorraine would have been raped, and George probably would have become even more afraid.

    What does George do? 

  • We see the McFly household in the improved timeline has a lot more money, no doubt because of George's new assertive attitude and powerful work ethic but it's mentioned that George just had his first novel published 30 years later. Was it mentioned what his new day job was? Was it freelance writer, or did he write for the Hill Valley times or something?
    • In the second movie the newspaper article outlining his death — chronologically published several years before the year the movie is set in — describes him as a local writer. Presumably he worked freelance.
    • Alternately, many English majors and writers go into/start off teaching. George could've made a living as a college professor (possibly of literature or creative writing) while waiting for his big break.

    Biff's job 

  • Why in 1985A does Biff decide to go into a car detailing business instead of being a supervisor at whatever job they were both at in the original? What changed in him specifically?
    • Probably because he never got a job there in that timeline. In the original timeline, it's implied he's the supervisor because he pushes George around to do all his work. In the new timeline, even if he's not less confident about pushing people around to begin with, since George isn't there Biff's own incompetence is more easily exposed.
    • A scene from the second movie shows Biff arguing with an auto detailer over the amount of money he's being charged for the repairs on his car after the first manure truck accident. That probably inspired Biff into pursuing that career.

    Doc still inviting Marty to the Mall after having met him in 1955 

  • Doc, having met him 30 years earlier, knows that Marty'll be accidentally sent to the past if he invites him to his parking lot time travel experiment. Why doesn't he just not invite him and spare everyone the trouble? It doesn't make any sense that Doc would act the exact same way and do the exact same things in the 80s given what he learned in the 50s unless he WANTS Marty to be sent back.
    • If Doc doesn't invite him, he creates a paradox.
    • This may be a case of You Already Changed the Past. Notice how at the start of the movie, Doc urges Marty to be at the mall at a very specific time. If his plan was just to demonstrate time travel with his dog, then why would that time be so important at all?
      • The time is important because the mall parking lot is completely empty at 1 am. Doc needs a huge, wide-open and paved space to demonstrate the time machine.
      • Time travel does not work that way in BTTF. Doc has no knowledge that Marty "will" end up stuck in 1955 "before" Marty actually goes there and back again, and the new timeline overwrites the old one. We see that the old timeline developed as if Marty was never there (screwed-up family, Twin Pines Mall), so why would Doc be different?
    • Doc knows that, back in 1955, one time-lost Marty was sent to 1985. What would happen if he didn't send the 1985 Marty to the past? Well, 1955 Marty would appear anyway, and then... imagine him getting into his own bedroom and, instead of finding a girl of an Afro-American family, he finds another version of himself. Great Scott!

    Einstein being a lab rat 

  • Doc, don't you want to make absolutely, positively sure that time travel won't harm living creatures before you use your dog to test your machine? Maybe send a lab rat or something back first instead of your beloved pet?
    • He knows it is safe and works, Marty told him so in 1955.
      • If he knew it was safe why send a dog instead of himself?
      • As a scientist, he needs to be outside observing. Also, he's making a recording of the experiment
    • Remember also that Doc is from a generation of scientists that did things like shoot dogs, chimps and cats into space. Animal welfare was... not exactly a high concern at that time.
      • Yes, but... sentiments. Presumably even people from those times would be more hesitant to experiment with their pet than a random animal.

    Don't stop, drive! 

  • Why is the couple in the car, the first people Marty meets in 1955 after Peabody's family, so hostile/scared of him? He's just a kid in a life vest.
    • It's a radiation suit, not a life vest. Just a few scenes later, Doc himself asks "what on earth is this thing I'm wearing?" when Marty shows him the video footage from 1985. If a scientist can't identify a radiation suit, then it's doubtful that some old couple in their 60s or 70s can. Considering he's by himself in the middle of the road on a Sunday morning wearing this bizarre suit, it's understandable that the old couple would freak out. After all, he might be a Commie.
    • There was a bit of a moral panic about wild, out-of-control teenage kids in the 1950s, and this is a teenage kid in a strange costume approaching them on an abandoned road. The couple assumed he was hopped up on something and panicked.
    • Also keep in mind a DeLorean looks wildly different from any car in the fifties. Mistaking it for a spaceship might be over the top, but thinking it's at least some sort of crazy government experiment seems probable.
      • But would there be reason to be scared of a government experiment, though? It might be out of the ordinary, but you'd know (or believe) it's still human in origin.

    Can't Marty just take the car for another round? 

  • Marty couldn't warn Doc about the Libyans shoot him, but luckily he read the letter and wore a bulletproof vest. But even if Doc hadn't taken precautions, surely this wouldn't have mattered? Marty still had a DeLorean - and, as we see at the beginning of the movie, Doc's plutonium supply is nearby; so surely, Marty could have retrieved some plutonium, put it in the DeLorean to power it, then gone back, say 30 minutes this time, and warned him properly?
    • The car is, at that stage, bricked. The engine was malfunctioning, so Marty would need to get someone to tow it, and a mechanic to fix it, without drawing unwanted attention about all the attachments. Then, consider the last trip is done with the car jury-rigged to power the time circuits from a lightning bolt. That must have required some tinkering, and it's very unlikely that Marty, knowing nothing of the inner workings of the machine, could undo the modifications and have it work from the plutonium reactor again.

    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). However, both Lorraine and Strickland warn Marty against spending time with him. Strickland is something of a jerk, and could perhaps just not have a taste for scientists, but there's no real reason Lorraine would be so dismissive of the Doc.
    • He's still an eccentric weirdo; just because someone's won an award for science doesn't mean that they're necessarily a good role model for your kids to hang out with.
    • Lorraine is never shown to be dismissive of Doc Brown. Original timeline Lorraine disapproves of Marty's relationship with Jennifer but 1985 Lorraine of any timeline never mentions Doc Brown ever.
    • The award happened a while ago. The impression is that Doc, after hitting his head, slowly went mad (or so it seemed to people) over the next 30 years trying to invent the time machine.
      • According to the newspaper in Part II, the award was in 1983, only two years before the film and well after hitting his head. It's possible that 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.
    • Even if they have nothing in particular against Doc Brown, it's not unreasonable for Marty's parents to disapprove of Marty spending so much time with the man that it's making him late for school.

    Libyans finding Doc 

  • How did the Libyans know that Doc Brown was at the mall in the first place?
    • Doc himself didn't know, why would we?
    • There could be any number of ways. Doc Brown was in the phone book and his address was well known. Perhaps they went to his home first, and when he wasn't there they searched the place until they found a clue to Twin Pines Mall. Or they just drove around until they found his truck. There's no evidence that they had one, but if the Libyans had a Geiger counter they would have been able to use it to find the plutonium.
    • More likely, they knew that Marty was Doc's best friend and had someone following him. As soon as their lookout spotted Doc and Marty at the mall, they called the Libyans who hightailed it over to the mall. That would explain why they showed up when they did.
      • There's no indication that the Libyans knew who Marty was, let alone that he was friends with Doc. Them trying to shoot him was most likely just to leave no witnesses.
    • They could have found where he lived and tapped his phone. That would let them hear exactly where Doc said he would be at exactly what time.

    When Doc drives out the truck in the car 

  • When the van opens up and gives us our first spectacular look at the DeLorean, reversing it out if the van and opening those glorious doors skyward while Doc Brown steps out. While a great shot, since the DeLorean's doors are opening up, rather than out- how did Doc get inside the car? There wasn't enough room inside the van to accommodate for one of those doors opening up. Did he really get in the car while he was outside and drive it into the van, just to back it out just so he could unveil it to Marty?
    • Doc has a flair for the theatrical?
    • The gull wing doors of the DeLorean actually don't require as much horizontal clearance to open as it seems.
    • Or Doc modified the side of the van with an opening section to make ingress/egress easier.

    Music 

  • What song is used by Darth Vader from planet Vulcan to fry George's brain?
    • Apparently it was just a random guitar solo that Eddie Van Halen specifically made for the movie.

  • As a non-musician, is "Okay guys, this is a blues riff in b, watch me for the changes and try and keep up okay?" enough information for the Starlighters to play a song they never heard before absolutely perfectly, sax riffs and everything?
    • Yes. Twelve bar Blues, sometimes just called Blues (which "Johnny B Goode" is,) is extremely common, even for 1955. You'll find that there are many blues jams today where people just improvise over a known beat and style. The easiest method for someone is to use the "Blues scale" (a modified minor pentatonic scale) although there are many other ways to riff over basic twelve bar Blues. Any R&B band worth hiring would know how to play that progression.
    • As for the sax riffs matching, the gag is that the song is a Stable Time Loop. Chuck Berry got an earful of Marty's performance from his cousin's phone call and copied them when he recorded the song. Which makes the Starlighters' sax player the actual composer for those riffs, albeit uncredited.

    Dave's still living with his parents 

  • In the original timeline, Dave (Marty's brother) is depicted as a loser, which would explain why he's working at some fast food joint and living with his parents even though he appears to be in his mid-20s. But in the altered timeline at the movie's end, he's now a successful yuppie with a nice suit, yet he's still living at his parents' place. What's up with that?
    • Who said Dave has a permanent residence? He could just be visiting, or changing homes.
    • Or his job didn't require him to move from home, so he's taking advantage of the free room and board to save up more than if he'd had to rent an apartment.
    • There are plenty of people who still live with their parents into their twenties. According to the card game, Dave is 22 at the time, so he probably just got out of college a few months prior.

    Implausible odds? 

  • What were the odds that the day that Doc invented time travel just happened to be the same day that Marty's parents met?
    • David Hand's Improbability Principle. In short, you'd likely ask the same question if it was any other significant event in Marty's life: his parents getting married, him getting born, one or the other moving into Hill Valley...heck, you'd probably ask if any significant event in Marty's life happened on November 5th. So the odds for this specific combo is low, but the odds for anything we'd point as "unusual" is quite high.

    Which way is the direction of Hill Valley? 

  • When Marty rides home from the town square at the beginning of the movie he comes in from the audience's right to pull into Lyon Estates. However when Marty goes back to 1955 and he sees his future home, he is riding in from the same direction. Then he continues forward, to the left of Lyon Estates and eventually arrives at the town square. So did he make a significant detour while riding home at the beginning?
    • There was a road that didn't exist in 1955 that cut time, perhaps.

    John F. Kennedy drive 

  • When Marty referred to Riverside Drive as John F. Kennedy Drive, why did his grandfather say, "Who the hell is John F. Kennedy?" as if you're supposed to know who streets are named after? Why not say, "Never heard of that street?"
    • Because typically, if a street has a full name and middle initial, it's named after someone extremely well-known. John F. Kennedy was still a fairly obscure US Senator in 1955.

    The jacket 

  • When Marty and Lorraine were in the car at the dance, Lorraine was wearing a white jacket that she removed before Biff showed up. After George punches out Biff and he and Lorraine walk to the dance, the jacket was left behind in the car. However, when Marty says his goodbyes to George and Lorraine, George puts that jacket Lorraine had over her shoulders. (And yes, it is Lorraine's and not George's since George was holding his over his shoulder.) How did they get it? They didn't have during the dance and they couldn't have gone to get it after Marty finished playing the guitar since Part II shows that he walked off stage immediately after his "your kids are going to love it" comment.

    Calling the cops on Biff 

  • Why doesn't anyone call the cops or something on Biff after George prevents him from raping Lorraine? Yeah, it was the Fifties, but people back then weren't so unenlightened as to seriously think (attempted) rape is a-O.K. What gives?
    • People didn't "think it was a-O.K." George just figured getting decked and knocked out was punishment enough and nobody else saw it.
    • At the time, date rape could incur a heavy stigma for the victim. Accusing Biff, even with George as a witness, would have hurt Lorraine's reputation and probably incurred all sorts of counter-accusations about her "asking for it". Not something she'd want to go through or George would want to see her subjected to.

    Wearing a suit to the office 

  • At the end of the first movie, Dave says that he "always wears a suit to the office". Does he also typically go to the office on Saturdays?
    • Maybe he had an extraordinary meeting on that day.
    • There are businesses and offices open on the weekends by necessity. Daily newspapers, for instance, or utilities companies.

    Is Lorraine really a hypocrite? 

  • Lorraine's puritanical attitude about Jennifer before Marty goes to 1955 is almost always pointed to as hypocrisy on her part vis a vis the way she acts with Marty in 1955. But could it be that she wasn't that way in the first 1955? Maybe pursuing Marty for that week made her realize it wasn't a bad thing for a girl to go after a boy she liked, even if she came to realize Marty was all wrong for her. That would explain why her attitude in the new 1985 is the opposite of the original one. (And that original attitude, although puritanical, would at least be consistent with her original beliefs.)
    • Lorraine tries to jump Marty's bones as soon as he wakes up, and it's strongly implied she has done things like this before. So meeting Marty certainly didn't change her in that regard, she was already like that. "Do as I say, not as I do" mindset is not that uncommon with parents of teenagers; and it's relatively justified as folks would no doubt wish their offspring to grow up better than they did.
    • If so, why did Lorraine like Jennifer for the exact same reason why she disliked her before?
    • It must be remembered that Lorraine in the original timeline is clearly a rather bitter and unhappy woman stuck in a rather unhappy marriage to a man who can most generously be described as a wimp and a loser. Her dislike of Jennifer is seemingly because of her "promiscuity", but it's not a huge leap that on a deeper level it's actually because Jennifer reminds her of her lost youth and rather unsatisfying current circumstances, and she's just using that as an excuse. In the altered timeline, Lorraine lives a happy and fulfilling life with a confident and successful man, and so has no reason to feel any kind of bitterness or envy towards Jennifer. Hence, she is a lot more tolerant of any of Jennifer's perceived "faults" and a lot more willing to like her.

     300 dollars 

  • $300 (the cost of Biff's car repair after the manure incident) in 1955 dollars is almost $2,700 in 2016 dollars. It's extremely unlikely Biff would have had that much money, and if he did, he could have bought a decent replacement used car for less.
    • Perhaps young Biff did have that much money. He lived with his grandmother, and yet seemed to have no economic problems and in fact was a high school kid who owned a car in 1955. We know from the alternate 1985 Biff that he has zero qualms about commiting crimes for personal gain, so who knows what kind of illicit business he ran along with his three friends.
    • Do remember that when Biff learns that, his immediate response is to start ranting furiously about how ridiculously expensive this is and start arguing with the mechanic about it, so at minimum it shows $300 is not a sum he can afford to drop at a whim.

    Pepsi Free 

  • Pepsi Free was introduced in 1982, when Marty would’ve been 14, so surely Marty would know Pepsi Free didn’t exist in 1955.
    • Who's to say he did know? Most people don't keep track of when soft drinks were invented, especially if it's a variation of an existing product rather than a new one. Plus, Marty was freaked out and disoriented. He walks into a diner, he's on autopilot and orders what he always orders.

    Marty looks exactly like Calvin 

  • About George. Wouldn't his son growing up to be the spitting image of his wife's high school crush be enough to make him certain he's been cheated on? She even named him after the guy's nickname!
    • Marty wouldn't be born for some 13 years after 'Calvin' completely disappeared from their lives. Plus they only knew the guy for a week. It's unlikely that either of them remember exactly what he looked like by the time Marty grows into a teenager.
    • The third movie also reveals that George's ancestors, Seamus and William McFly, looked like Marty, so he will more likely think that Marty is the spitting image of them.
    • Maybe George thought (not entirely incorrectly) Calvin was some human disguise and was actually "Darth Vader from the Planet Vulcan".

    The Marty from the improved 1985 A timeline 

  • When Marty returns to 1985 at the end of BTTF and finds out that his entire family is different... where the hell is 1985' Marty? BTTF2 and the Telltale games establish that each version of 1985 has a Marty that is doing stuff (run out of town, run out of town again, camping, what have you), but won't they eventually return? And if they somehow vanish when original Marty appears, he isn't getting the new memories of those timelines, so even when he finally gets back to 1985, his life could potentially be very different, and he wouldn't know what he should.
    • At the end of BTTF, Marty returns to see the "new" Marty leave in the time machine as Doc is shot at by the Libyans. Where that Marty went at that point is subject to Wild Mass Guessing.
      • Possible Fridge Horror: That Marty went back to the same week, but was a Marty of an alternate timeline, henceforth events played out differently and (assuming this new Marty made it back at all) he too would be coming back to an entirely alternate timeline from Marty-A.
    • Way back before the second film came out, Starlog magazine published an article that suggested what might have happened to the Marty we see departing at the end. Because he owns the truck, he's a better driver than the Marty the movie follows so he doesn't lose control of the DeLorean and avoids crashing into the barn. The Doc he's left behind knows what is going to happen to him in the past so has stored an extra charge of plutonium in the car. Marty simply loads it up and returns to 1985. Thus he never interacts with his parents and history unfolds as it did first time round. Which means he wound up in the original timeline that our Marty departed from.
    • The answer to this is a lot simpler than people make it out to be. While the 1985 that "our" Marty ends up in is different, the past that 1985A Marty arrives in is the same one "our" Marty arrived at the beginning of the movie. 1985A Marty will go on to do almost the exact same things that "our" Marty did, with only some minor differences (such as, he will be astonished to discover that his cool and confident dad in the past was actually a clueless dork, and so on), and will return back to the same 1985A timeline having accomplished what the original "our" Marty did, with the only difference being that instead of creating that timeline as "our" Marty did, 1985A Marty is simply ensuring that timeline.
    • Perhaps peoples' memories do get replaced though, it's just not shown in the movies. It gives a nice Watsonian explanation to why in the following films Marty's personality changes to reflect his new upbringing, why Jennifer in the second movie looks different yet Marty didn't remark on it, and why (when Doc and Marty encounter the bad Biff timeline) Doc insisted on going back to 1955 to fix the corrupted timeline immediately, even though the time circuits on the DeLorean were acting up.

    Marty not telling Lorraine: I have a girlfriend 

  • When in 1955, Marty had a picture of him and his siblings with him. Why couldn't he just claim to Lorraine that the woman in the picture was his girlfriend? With "Calvin" already "taken", it could have caused her to move on.
    • His sister was wearing a sweatshirt that said "Class of 1984", and his brother's head had already faded from the photo by the time Marty realized what was going on. That would have raised awkward questions.

  • Then again, why didn’t Marty tell Lorraine about Jennifer? Lorraine would know Marty had a girlfriend, which would be a good reason for her to give up on him.
    • Once Marty realized his existence was in danger, he was mostly focused on getting George to ask her out and didn't really interact with Lorraine until she asked him to the dance, which he went along with when he came up with a new plan.

    Marty and Lorraine in the same room 

  • Marty being in Lorraine's room: It makes no sense that the Baines family would put Marty in the same room with their same-age daughter considering 1955 society and moral standards, especially considering the Baines family had several sons. Lorraine's parents would have put Marty in a room with the boys, not with Lorraine.
    • Teenage Lorraine is shown to be both something of a fast-talker and good at playing the innocent, sweet girl in front of her parents. Besides, she had been the one to volunteer to take care of him while he was knocked out, so she would have been alone with him whether she was in her own room or her brother's.

    Doc asking who's president 

  • Why did Doc think asking about who was President in 1985 would clear anything up? They sometimes ask people about the President to check their memories or mental state, but when Marty brings up Reagan, Doc just blows him off.
    • Trying to trip him up. For a certain % of the population possible to tell if they're telling the truth based on how quickly and confidently they reply.
    • The name of the President is probably the one public name that almost any US citizen would likely be able to rattle off almost instantly, so Doc used it as a simple test. As for why Doc blows off Marty as soon as he mentions Reagan, it's because in 1955 Ronald Reagan was still mainly known as an actor and hadn't seriously entered politics (he wouldn't win public office until he became Governor of California in 1967) and the likelihood of him becoming President was considered, well, about likely as someone believing in 1985 that Donald Trump would one day be President. Doc is simply assuming that Marty is latching onto the first reasonably well-known name he can think of to try and bluff his way past the question, and is scornful that Marty can't even name a more likely figure. Ironically, had the President in 1985 been someone less well-known in 1955, Doc may even have started to believe Marty a bit sooner.

    Biff tried to murder Marty 

  • Some people have rightfully called out the show for hand-waving away Biff's attempt to rape Lorraine, but everyone in the movie and in real life seems to totally dismiss Biff's more serious crime: Attempted murder. Biff tried to run Marty over with his car, repeatedly, in broad daylight, in front of dozens of witnesses. And no one seems to mind at all. No one calls the police. No one expresses any dismay. None of Biff's classmates are concerned that he literally tried to kill someone. Why is a blatant murder attempt so casually dismissed?
    • He was going to ram Marty into a manure truck. Was he intending to humiliate him? Yes. Trying to kill him? No.

    Paradoxes 

  • The Grandfather Paradox no-one wants to talk about. In the first movie, Marty stops his parents getting together. This will lead to him disappearing, as he never existed in the new timeline in the first place. But, if he disappears, presumably he never existed to stop his parents getting together in the first place. So, logically this changes the timeline again, seeing as the new timeline cannot logically occur (no Marty to cause the change in the first place). Does this mean the timeline would eventually reset itself back to the original? If so, why is there any need for a story?
    • Or it might wipe out the timeline entirely when it can't reconcile itself. Doc mentions this as a possibility.
    • It could be that this is the reason why Marty has time to fix the issue. The immediate expedient of causing him to cease to exist would trigger a paradox to destroy the universe. But time is just a facet of the universe. Marty can't destroy something so massive so quickly. So if there's a way for the causality to work out so that the universe continues existing (i.e. Marty getting his parents to hook up) the universe can hold together long enough for that possibility to play out.
    • Given how the timeline holds together in certain ways - for example there's no repercussions for Marty and Doc effectively erasing their reasons to travel back to 1955 by burning the almanac, thus preventing 1985A - perhaps the timeline would have simply continued if Marty was erased, with him, from the perspective of the timeline, effectively briefly existing to ensure his own nonexistence.

    Fading 

  • What's with the weird way fading works? Marty might have been able to remember his brother and sister Dave and Linda having been in the photo, but what sense does them gradually fading bit by bit have? It's summed up well in this comic. When Dave's head disappeared in the photo, does that mean for a few days there was a timeline where Dave had no head?
    • Evidently the Delayed Ripple Effect takes its time in this universe. Arguably even the notion of only Dave fading is odd, since logic says that if they don't get together none of the three should've been born.
    • WMG: The picture depicts the most probable outcome, and Lorraine and George might've still gotten together without Marty's help sometime after November 12 1955, but perhaps not in time for Dave to be born. There's evidence supporting this in Part III: when "Mad Dog" Tannen arrives at the saloon and calls out Marty for their showdown, Marty hesitates and looks at the photograph of the tombstone. The tombstone was previously blank, but the name "Clint Eastwood" (Marty's alias) begins to fade into view, indicating that he will die if he goes out, not an unreasonable assumption.

  • Also, Dave seemed to have taken half the week to disappear, Linda most of the other half, and Marty took less than an hour?
    • It's due to how as time progressed it became less likely for George and Lorraine to be a couple, so it sped up as the changed timeline drifted further and further away from the one that resulted in the photo. It also neatly explains why everyone faded back into the picture so quickly at the Enchantment Under The Sea dance, because the events of the future were now 'set', so to speak.

  • Why does Marty start fading when he does? After George fought Biff, took Lorraine inside, started dancing and got pushed away by a bully, Marty starts fading, which implies that George is about to give up and be a milquetoast. But with no intervention from Marty or Doc George gains courage to stand up to the bully and kiss Lorraine, then Marty is fine.
    • It was still a result of Marty's time traveling, stopping his father from being hit by a car one week ago. At that moment, it looked like the most likely future was one where George gave up and went home, thus Marty fading. However, when George changed his mind and went back, the most likely future was one where Marty and his siblings were born.
    • The being-interrupted-by-a-bully part seemed actually a result of Marty's intervening. In the original timeline, no one thought it was "worth" trying to grab George's girl at the dance, because, well, she's with George McFly. After Marty sets in motion the chain of events leading to George decking Biff, now someone wants to make a name for himself by challenging the guy who stood up to Biff Tannen. Marty is fading because the critical moment that ensures his future (George kissing Lorraine at the dance) hasn't happened yet, and the decision is still up to George, whether the newfound confidence and assertiveness Marty helped him to discover will remain, or whether he'll revert to his lifetime of meek passivity. Until George himself makes that choice, Marty keeps fading.

    Marty's name 

  • At the end of the first movie, Marty tells Lorraine his real name. Lorraine clearly likes the name, implying she will eventually call her child that. The only thing... Marty was not her firstborn son. So why didn't Dave end up being called Marty and Marty end up being called something else?
    • Maybe she liked the name Dave even more.
    • Dave was her previous fling. She certainly had at least one boyfriend prior to Marty, given that she said "it's not like I've never parked before."
    • Or perhaps he was named after a relative, who probably trumps a friend that you haven't seen in years in importance.
    • Maybe George chose the name of the firstborn son. Then Lorraine chose it for the second son.
    • Pop-up trivia information on the DVD of Part III says that Marty's having an ancestor by his own name is an indication that he was likely named Martin partially after that guy as well.
      • That raises another question: Why did George name his son after an indirect ancestor who died over half a century before George was even born?
      • Because it's a nice name. Because Martin McFly was the original McFly to settle in American and George felt like honoring him. Because it's a family tradition in some way. Any number of possible reasons, really.

    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.

    Biff was OK with George dating Lorraine? 

  • Biff likes Lorraine, so in the original timeline why didn't he tell George to quit dating Lorraine? And since Original Timeline George was incapable of standing up to Biff, he would have caved in and they never would have gotten married.
    • Maybe Lorraine did all the standing up to Biff.
    • Biff in the original timeline didn't really like Lorraine, only wanted to get in her pants in that one scene. Likely he wasn't interested in some sad lady who falls for the lowest common denominator (George), but after Marty influenced George to stand up and become successful, Biff now wanted Lorraine.
      • Biff clearly has a thing for Lorraine even in the original timeline ("Say hi to your mom for me.").
      • Even if Biff doesn't want to get involved with her due to her supposed poor taste, that doesn't stop him from continuing to make some passes at her. This is Biff after all.
    • Biff probably doesn't want to be married to Lorraine, he more than likely just wants to have sex with her. Honestly, wouldn't put it past him to have an affair with Lorraine (or try to, anyway) just to humiliate George further.

    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. 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.

    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.

     0 AD 

  • At one point, Doc sets the time circuits to the year "0000", which doesn't exist (1BC was followed by 1AD). What would happen if the DeLorean had tried to travel to that time?
    • Presumably, it would extrapolate the year from its dating system and thus arrive in 1 BC.
    • Wikipedia states that "astronomical year numbering" has a year 0 (what we would call 1 BC), and then it continues counting into the negatives -1, -2 etc.. Maybe the DeLorean is set to astronomical time.

    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.

    Hitting 88 at the same time as the lightning 

  • In the finale, the Delorean is tearing down the street towards the wire. But is there any reason (outside of time and available parts) why Marty and the Doc couldn't just build a rudimentary treadmill of sorts, mount the Delorean on it, with cable running from the clock tower and directly into the Delorean's machinery? That way there'd be no concern about driving it up to speed, they could've just had it stationary with the wheels spinning at 88 until the lightning hit. Hell, this same solution would also solve their fiasco in part III.
    • The car has to be moving 88 MPH. Not just its wheels spinning at 88 MPH.

    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.

    Hill Valley's got weird zoning laws 

  • We know from the newspaper clippings seen in the opening that Brown Mansion burned down and that Doc subsequently moved into his garage, selling the rest of the land to developers. However, the scene where Marty leaves the garage in 1985 shows that these developments have resulted in Doc having his residence in the middle of what is clearly a commercial district. Would any kind of zoning commission allow this?

    Libyans in Hill Valley? 

  • What were a couple of Libyan terrorists doing in Hill Valley, which seems to be an at least somewhat obscure place, anyway? Did they deliberately seek out the Doc knowing that he could build them a bomb?
    • The intended interpretation seems to be that Doc traveled to Libya to scam the terrorists, and they simply tracked Doc down back to California.
    • People who have suspicious and illegal transactions to make would probably prefer the more obscure, the better. As such, if you're arranging to acquire some stolen plutonium for a terrorist plot, then why not some quiet, obscure little town where no one's really going to be on the lookout for that kind of thing?

    Biff should be locked up 

  • How does someone with obvious homicidal/sociopathic tendencies get to run around free as a bird without any kind of recourse? Young Biff was willing to run over another human being in full view of the public, as well as trying to run the same human being into a tunnel wall with his car a few nights later. He also tried to rape another student. Older Biff was an unapologetic drunk driver. Why is he not in a sanitarium for the criminally insane?
    • It was The '50s. Stuff like that happened a lot.
    • He didn't * succeed* at those crimes, so he couldn't be charged with them. Maybe with attempting them, but that wouldn't automatically land him in a sanitarium (he clearly isn't insane), and even if it did he might be out of it even more quickly than in prison. It's not like someone is likely to go to prison for life just for *attempted* murder or rape, and those who witnessed it might have been too afraid of him to come forth with it. The direct victims seem not to have pressed charges.
    • As mentioned in an above headscratcher, he was trying to humiliate Marty by ramming him into a pile of manure, not kill him. Then consider his other two crimes, trying to ram Marty against a tunnel and raping Lorraine, did not really have witnesses. In fact, given Biff in original 1985 was stated to get George to do all his work for him, he likely was well aware of the methods to get away with what he does.
    • Considering also that Biff's intended victim was Marty, who couldn't press charges because (1) he wasn't supposed to exist (what would he do if the police or judge asked him for ID?), and (2) Doc wouldn't have allowed him to, as it would screw up the timeline (not to mention that, after the first manure-truck crash, if Marty had pressed charges, the trial would probably be scheduled after Marty would have to hit the lightning bolt at the clock tower to go back to the future).
    • Maybe he did spend the night in jail after crashing into the manure truck, and his grandmother had to come bail him out. It could explain why she always sounds so grumpy whenever she asks him where he's going ("BIFF! Where ya going this time?!?").
    • Isn't he implied to be a high school football star? Cops have certainly cut corners for guys like that in real life small towns, it wouldn't be surprising if it was the same there.

    Setting fire to the rug 

  • Before he heads off to make his run back to the future (heh), Marty tells his parents that if they ever have kids and if one of them when he's eight years old accidentally sets fire to the living room rug to go easy on him, the implication is that Marty's referring to himself. Only problem: if, as is implied, Marty does retain his memories of the 1985 timeline only, and doesn't gain the memories of the 1985A timeline, how does this affect his own life? More to the point, why the hell, having just barely avoided fading out from his own messing around with the timeline, having been warned repeatedly by Doc that he's not to interact unnecessarily with people from his own past, would he then consciously do something which could potentially start the damn problem all over again?
    • Marty wouldn't actually know at that point how the memory thing works. Even if it doesn't, if "you" are about to walk into a puddle, are you-you going to stand by and do nothing? As for why he'd do something that would risk messing up the timeline... well, Marty's never really been concerned about that sort of thing.

    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.

    Darth Vader from Vulcan 

  • So when Marty pretends to be Darth Vader hailing from the planet Vulcan to scare George into going out with Lorraine, that inspires George to write a story about it later. However, after seeing the Star Wars and Star Trek franchise used two things that he would have used in the story does he ever wonder if they too were visited by the same alien? if so, would he try to get in contact with the creator of that franchise to talk to them about that only to be laughed at?
    • Star Trek didn't invent the idea of Vulcan; it's been floating around for a while before being popularised by Star Trek. The Vulcan salute was likewise drawn by Nimoy on his Jewish background and the hand gestures used by rabbis in synagogue ceremonies to incorporate that into the character of Spock. So neither would've set off alarm bells.
    • By the time George has published the science fiction story which is (presumably) based on his 1955 experience, Star Wars has already been out for almost ten years. It's quite possible that he was saving the Darth Vader name for that, but then when Star Wars came out he thought "Dang it, some one else used it first" and changed it.
    • It's even possible George no longer believes the thing really happened (i.e. that the whole thing was just a bizarre dream), but still considers it a fine yarn on which to base a novel.
    • Perhaps George waited so long to write the book because he was afraid that Darth Vader the Vulcan would be pissed if he blabbed about his "encounter", and only did so because other writers had successfully used those names without interplanetary repercussions?

    Why is the Clock Tower worth saving? 

  • Regarding "Save the Clock Tower" foundation. It was struck by lightning, a natural accident. How does that make it worth keeping broken?
    • The Mayor was planning to replace it with an entirely new clock. Since the old one had been around for 100 years, some people just wanted to keep it for the sake of tradition.
    • In one of the old scripts it said they were religious fundamentalists who didn't want the clocktower changed because God struck it with lightning and wanted it broken, or something like that.
    • It's also local historical point-of-interest. Granted, a point of interest to maybe only a small handful of people, but people have organized protest over smaller things.
    • This is not unheard of in Real Life. The old Christchurch Railway Station's clock (well, one of them) has been left to read 4:35 as a reminder of their earthquake.

    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.

    Libyan terrorist van 

  • Why do the Libyan Nationalists have a hippy van?
    • Because it was cheap and they could pay cash for it.
    • It's a Volkswagen! Those things are reliable. Just like AK series rifles. Oh, wait...
    • The terrorists are hippies. There were hippies who were terrorists, so the inverse would make as much sense.

    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.

    Do not open until 1985 

  • When Marty writes the letter to Doc in the first film, why does he write "Do not open until 1985" on the envelope? First, there wouldn't have been anything wrong with Doc opening the letter right after Marty had left anyway and secondly, all it did was tell Doc that Marty was trying to tell him about the future, prompting him to tear it up.
    • If Doc had read the letter before 1985, he would've known that terrorists were going to shoot him, and it may have prompted him to never initiate contact with the Libyans, which would've screwed up the timeline.
    • Also, since Doc is adamant about not knowing about the future, Marty probably thought that the only way to get him to read it is if it stops being about the future.

    Time travel fire tracks not burning? 

  • Why don't the fire tracks left by the DeLorean in the beginning of Part 1 burn Marty and Doc when they're standing right in them? If they're not fire, how come 1955 Doc specifically avoids them once he's sent Marty back to 1985?
    • It probably wasn't actually fire. After all, they trails still appear in the air, and physics indicates that if a gas (the air) is on fire it's probably start spreading out instead of remaining as a line. They could in fact be holes in the space-fabric left by the DeLorean. But because they look like fire, 1955 Doc avoids them.

    Doc's clock experiment 

  • What experiment is Doc conducting where he's elated that the clocks are running 25 minutes slow? Is he just messing with Marty?
    • Wild Mass Guessing: Doc's been doing test firings of the flux capacitor in the room to see how it affects the spacetime continuum in a very localized way. If the clocks hadn't all gone off at the same time, he'd have known the flux capacitor itself was damaging spacetime in some way, since he'd very precisely attuned all of them to go off at once.
    • Is it possible Marty inadvertently walked into an experiment that stopped time locally? It would explain the 25 minute disparity in the clocks, and why Marty managed to end up 25 minutes late despite only spending a few minutes there and having a watch.
    • Perhaps Doc started out with a small, prototype time machine. It wasn't big enough to hold a person (or even a dog), but it was big enough to hold a clock. So Doc got a bunch of clocks and synchronized them perfectly. Then he sent each of them through the prototype time machine individually, comparing their times in order to confirm that the trip was truly instantaneous. Then he kept all the clocks for a while and observed them each day, making sure that they stayed synchronized. He wanted to make sure there wasn't some sort of time dilation problem, where a clock would experience time differently even after it exited the machine.
    • An interesting Epileptic Tree on a fan site hypothesized that the Doc had been converting his clocks from sidereal time to solar time. It even had some math to back it up, and guessed that Doc would eventually go home to reset his clocks to the correct time.

    George's hair 

  • Why does George McFly dye his hair in the original, more pathetic timeline, but not in the improved timeline where he's a writer?
    • In the original timeline he's so self-conscious about his age and his lost years of amounting to nothing that he dyes his hair to avoid dealing with the fact it's greying. In the improved timeline he's a successful writer, at peace with himself and self-confident, so he doesn't feel the need to dye his hair at all.

    Doc meeting the Libyans 
  • How did Doc get into contact with the Libyan terrorists?
    • The terrorists probably sought him out. There can't be many people in a place like Hill Valley who have the know-how to build a nuclear bomb.
    • Word of God says in the DVD that they thought of Doc as having probably worked on the Manhattan Project. If the Libyans did their homework then they would likely have heard of him, so either they sought him out and he took advantage of the opportunity or he used his credentials to his advantage and sought them ought with his hoax already in mind.

    I hit someone again! 

  • Why does Lorraine's father (Marty's grandfather) complain that another teenager threw himself in front of the car? Has this happened before?
    • Yes. It seems plenty of horny teenagers, not just George, were eying his daughter as she changed.

    Is 1. 21 GW from plutonium and lightning even possible? 

  • Can a single lightning bolt generate 1,210,000,000 watts of electricity? Or can the small amount of plutonium seen in the first film? It sounds like an awful lot....
    • According to The Other Wiki, "The average peak power output of a single lightning strike is about one trillion watts — one "terawatt" (1012 W)". Enough to power hundreds of DeLoreans.
As for plutonium, assuming pure Pu-239 and fissioning 100% of it, it's enough to create 1.21GW for about 18.5 hours (in reality some of it would be transmuted into heavier isotopes and some would remain Pu-239 after the reactor has gone subcritical due to fuel depletion, but still, plenty of juice).

    Excuse me while I take off this radiation suit and touch the plutonium 

  • In the first movie when Doc and Marty are loading the plutonium into the DeLorean, they are wearing radiation suits to protect themselves from the plutonium. However, less than 10 seconds later after Doc and Marty have taken off their headgear, Doc opens up the chest full of plutonium to put them empty jar back, exposing himself to a severe, if not lethal dose of radiation.
    • The plutonium was in a tube like thing in the glass jar. When he loaded the plutonium, it was removed from the jar. The jar contained some sort of liquid (probably water, which is actually an extremely effective radiation shield), which presumably protects the handler from radiation. If you notice, the liquid is still in the jar after the plutonium is inserted into the car. It was only during the transfer that there would be possible exposure.

    George and Lorraine still have the same kids 

  • After the events of the first movie, Marty, Linda and Dave ALL should have ceased to exist. The odds that Confident George and Lorraine would have sex at the same times as their counterparts in the Twin Pines universe, so that the same ova and sperm meet to create the same individuals, are astronomically improbable.
    • Some people theorize that time has a way of putting things into place - it's usually not life-altering if you step on an ant or are five minutes late. Marty's interventions only took palce over a week, it likely hadn't affected what times they got married or stuff like that. It takes the altering of distinct and crucial events to really change something, like when Marty stopped his parents from meeting.
    • You could also argue that they're not the same individuals. Dave clearly has his act together far better in 1985A. We don't see enough about Linda to know how she's changed, but she undoubtedly has changed in some way just like the rest of the family. The only way in which they definitely haven't changed is in their looks.

    Doc's calculations for the De Lorean 

  • Doc rigs up an alarm clock on the dashboard of the DeLorean and tells Marty to "hit the gas" when it goes off so he'll reach the conducting wire at exactly the right moment. Not only were his calculations off (the car stalls until a few seconds after the alarm rings, yet Marty still hits the wire at the correct time), but it wouldn't even be possible for the calculations to be correct. The DeLorean is a manual; Marty would have to momentarily release the gas to upshift - and this makes the run impossible to time with any degree of repeatable accuracy.
    • Given that Marty hits 88 miles per hour before he hits the wire (you can see the bottom of the car light on fire like it does when it time travels), it's likely that Doc wasn't aware the DeLorean could accelerate faster than he assumed. It is a car from the future, after all.

    Something's got to be done about your kids! ...In 30 years! 

  • At the end of the first movie, why is Doc in such a hurry to get Marty and Jennifer back to the future to save their children? Chill out Doc, it's not gonna happen for another 30 years.
    • Doc might have got himself locked into a 'San Dimas Time' way of thinking and forgot that spending 10 minutes in 1985 isn't going to remove 10 minutes from 2015.
    • Doc's watch is syncronised to 2015, and he's calculated all the events down to the moment. Remember when he looks at his watch when the weather changes, and remember how its alarm goes off when it's time to go intercept Marty Jr.? Doc imposed San Dimas Time on himself.
    • Doc's already been to 2015 once and seen what happens to Marty and his family. His strict timetable might be to avoid running into his past self.
    • Some fanfics speculated that Doc could have meant to travel back to 10:30 at night rather than in the morning and he made a mistake with the time circuits. It would make sense given that he is usually discreet with time traveling. Perhaps his hurry could be him realizing his mistake and trying to leave before anyone saw the time machine (although that didn't work with Biff seeing it).

    Donation money 

  • Why do the people wanting to save the clock tower ask for donations? They want the clock to stay broken, what's the money for?
    • It's probably for maintenance. If the mayor wants it gone, he likely cut public funds for keeping it from falling apart so they made up for it with donations.
    • Donations probably help pay for things like the flyers, for signs if they do protests, materials and gas if they go around asking for signatures on petitions, potentially lawmakers to have the clock tower designated a historical landmark, or (more cynically) to pay the head of the Save The Clock Tower foundation a salary that they don't really deserve.

    Marty's terrible sleeping posture 

  • How is Marty not in pain when he wakes up? In the real world, anyone who slept like that would have some serious shoulder and arm issues. Kind of disconcerting with the knowledge that playing guitar is Marty's favorite thing in the world to do.
    • If memory serves, he is seen rolling and rubbing his shoulder a few times after waking up, as if getting rid of some stiffness.
    • Well, in Real Life Michael J. Fox got Parkinson's. This just got depressing, but Marty might suffer the same thing.

     Wait until 1985 to read the letter 
  • The note Marty wrote to Doc about the terrorist shooting. Knowing too much about your future could be messing up the space time continuum, but...Marty wrote on the envelope that it shouldn't be opened until 1985, so if Doc just preserved the envelope somewhere safe and patiently waited until 30 years later, there wouldn't be any problem reading it, as it would be informing about the near-present time.
    • Time travel doesn't work that way. Knowing something about the future "sets in in stone", so to speak, and it doesn't matter if the event takes place 30 years or 30 seconds later - it's something that now must happen.
Tying into Fridge Brilliance, Doc may have remembered what Marty said about George standing up to Biff, and looked at the photograph, realising that it was still there and come to the conclusion that there was no harm in little changes now and then, hence him taping the letter back together.

    Johnny B. Goode 

  • The segment where Marty is playing "Johnny B. Goode" for the teenagers of 1955, and Marty says "Maybe you guys aren't ready for that yet...but your kids are gonna love it." Quick Google says the single came out just three years after that Enchantment Under the Sea Dance, and it that time the teenagers would be just 20 years old, meaning, still young people. It would make more sense if it came out about 10-20 years later to consider it more suitable for their children's tastes, but it's not much later from their own young years. Why wouldn't the young people of '55 enjoy this song?
    • The audience actually enjoys the rendition of "Johnny B. Goode" hugely, it's just the last 30 seconds or so when Marty plays his great big, Van Halen-esque guitar solo that he lost the crowd, and the other band members.
    • Also, Marty is not an expert about the past, he has no way to know the data you do know. He probably just thought they didn't were ready for that kind of music (when in fact it was his heavy metal antics what pulls them off), Marty is an high school age teenager, is normal he would make mistakes like that.

    Why didn't Doc figure out the Libyan fiasco? 

  • Doc should have been able to figure out most of what the letter told him, before he even read it. He watched the entire videotape, which ended with older Doc saying "Oh my God. They've found me—I don't know how, but they've found me... RUN FOR IT, MARTY!!!" - which is extremely ominous. And he was seen repeatedly rewinding and rewatching that scene, so he was clearly pondering it. Furthermore, he saw how frantic/adamant Marty was to tell him about the event, and Marty even says outright "Your life depends on it!" Even a non-genius should be able to figure out he was going to die that night. It seems glaringly obvious based on the clues he was given, even before he looked at the letter.
    • Doc Brown is established throughout the franchise as not being terribly bright and having a tough time figuring things out, that's probably why. A bit of willful ignorance not wanting to know things he shouldn't probably helped (or didn't help).
    • Doc didn't need the letter to tell him something bad was likely to happen, but he did need it to specifically know he was going to get shot (as opposed to kidnapped, run over by the Lybians' van, etc). Reading the note still gave him the chance to do something to avert that particular fate.

     Did Marty McFly actually attend the high school? 

  • Did Marty actually attend high school for a week when befriending George McFly and trying to set up his parents? If he did so, wouldn't teachers have asked what he was doing there and did any administrators ask for his transfer papers?
    • Things were a lot looser in the 1950s, to the point where Doc probably could have just claimed that Marty was his nephew or something, staying with him for a short period, and that his papers hadn't arrived yet. Doc's presence at the High School would suggest that possibility, the other is that Marty just hung around at lunch recess and the school was large enough that all the teachers just assumed he was a kid they hadn't really noticed before. The bits we get from the movie means that both explanations could be potentially valid.

     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?

     What would happen if the De Lorean 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
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