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Time Travel paradoxes work based on uncertainty.
So Marty screws up his parents meeting but isn't immediately erased, but as time goes on slowly him and his siblings fade out of a picture until they cease to exist. It's never really explained how this works, but this Troper has come to suspect its a mix of probability and uncertainty. See, regardless of what Marty did, there was a chance his parents would still get together regardless of his interference in history, but as time goes on that probability continually drops as things diverge from the original version of events taking the form of things slowly fading out of recorded media. Eventually there comes a point where the future either diverges from what Marty knows happened or it does not, a critical period so to speak, at which point he must either exist or cease to be based on what has happened which allowed Marty to exist up to that point.

Similarly, old Biff from 2015 Hill Valley changed his own past enough that he himself would no longer exist. If he had realized this was the case and not left the grace period between making the change and the changes becoming certain, he would have continued to exist, but the moment he passed the point of his changes being certain, he was almost immediately erased from the timeline.

In one timeline, Marty pulls off a successful Oedipus and becomes his own father.
This is the reason Marty's siblings were erased before he was. In one timeline, Marty, confused as hell, actually gave in and, you know, with his mother. He then decides to stay in 1955. He will then try to father alternate versions of his brother and sister, but because they would have inherited different genes from George than Marty did, they were impossible, thus they were gone the night of the dance. However, Marty was still possible. Unlikely but possible. Only possible through a sperm containing the exact half of the genes he inherited from his father joining with the exact same egg that made him. When he rejected this possible future in the car with his mother he began to erase himself again, because in that timeline his mother would go home from the dance disappointed. Only by either getting his mother and himself back together, or by getting his mother and his father together, could a timeline where Marty was possible come back into being.

Almost none of the films events actually take place.
Marty's brain is severely traumatized by the super-amp that blew him across the garage, sending him into a permanent fugue where he experiences all of the time travel adventures, despite actually being kept artificially alive in a hospital.

Doc risked his past by going back to warn Marty and Jennifer to fix their future.

First, it is Canon that, after surviving the bullets in the new version of 1985 at the end of Part 1, Doc decides to go forward in history. It is presumed that he does disappear from the timeline during his trip.

It may be presumed that everything else happens "normally" until he returns — the future that we see in Back to the Future II really happened the first time around. For example, the car accident that we see not happen at the end of Part 3 does.

Perhaps middle-aged-Marty's psychological problems are partly related to the trauma of Doc having disappeared.

Doc reads the newspaper article about Marty Jr in jail and decides he must prevent it. He goes back to 1985 and picks up Jennifer and Marty, then goes forward. This would have caused timeline alteration, including a no-Jennifer-and-Marty universe; but the ripple effect "hasn't happened yet", in accordance with BTTF metaphysics. They necessarily visit the exact same 2015 as the one from which Doc departed. It is only afterwards that things diverge, with the usual weird risks of paradoxes and whatnot, which is why the future of III is unknown in film canon.

The risk is more visible with old-Biff's adventures. He goes back in time and gives the almanac to himself. When he goes forwards, one would think he would arrive in a rich-Biff timeline. He doesn't because, since he left 1955 before the branching point when Marty either does or doesn't successfully take the almanac back, the changes haven't rippled forward as fast as Biff rippled out of the timeline... It may be presumed that he has the heart attack because the rich-Biff died in middle age.

  • Old Biff died and faded away because - in the timeline he created - Biff was killed in 1996, per a DVD special feature. Quite probably by Lorraine (or at her request).

Doc is a Chessmaster who planned out the entirety of Part II and III to ensure a better future for Marty
At the very end of the third movie, when Doc comes back in the train with his kids, Jennifer asks him about the fax, and the fact that it erased. He says of course it did, the future isn't written yet you can make it whatever you please. In my mind, this kinda cheapened the entire second movie. Why bother going to the future to change what happened to Marty Jr if the future isn't set in stone and can be changed? wasn't pointless. Doc PLANNED the entire thing. Doc knew that Marty being a hothead about being called "chicken" resulted in a future that was...not really great. He wants Marty to get over this, but can't just say "You're going to be in a car race that Needles eggs you in to, you're going to hit a Rolls Royce and ruin your future." Doing that would cause problems, because as he says multiple times, no one should know too much about their own future. So instead, he comes up with a plan: set into action a chain of events that will cause Marty to mature, and get over his whole problem with being called chicken. So he uses his knowledge of how timelines and time travel works, and figures out this plan, that involves the entirety of BttF 2 AND 3, that eventually gets Marty to mature. His tombstone just HAPPENS to be next to where the DeLorean is buried in 1955? No...he planned it that way. He let it be known that is where he wanted to be buried, so that Marty would see the tombstone in 1955 and plan to come back to the past, and that the events of part 3 would happen and allow Marty to get over his issues and not get in that accident. Another part of the theory is the malfunctioning Time Circuits in part 2. They worked just fine, he simply made it look like they weren't so he'd have an excuse to be sent back to 1885. When he was trying to land the DeLorean in 1955 after Marty burned the book, he says that he has to fly back around due to the wind, but in what we've seen of the DeLorean flying previously, it seems like it is able to do a vertical landing, akin to a harrier jet. So why suddenly does the wind matter? It doesn't. Doc knows that if he stays in the air he will get hit by lightning, and has the time circuits ready to go to 1885, as it is all part of his perfectly thought-out plan.

Doc is a total bad-ass, and one of the greatest Chessmasters ever committed to film, using his own death as part of his plan.

  • "Why bother going to the future to change what happened to Marty Jr if the future isn't set in stone and can be changed?"

In a way, this question answers itself. Because the future can change… one may as well "bother" to change the future. It just happens that Doc is cautious enough to not want to change the future "too much", so he doesn't try to prevent the Marty-Jr-in-jail timeline by simply warning young Marty about his future son and waiting thirty years.

Apart from that, this is very clever, though of course like nearly any plan in both film and real life, there seem to be many many ways it could have gone wrong.

  • It probably "went wrong" several times. Doc knows how to redo things/warn himself without paradox.

The DeLorean's LED readout indicating the year is broken.
Specifically, the space which records the last digit of the year, which is why they can only travel to years ending in "5". (The time when Doc demonstrated the display with the years "1776" and "0000" was before it broke.)
  • Considering that there is no Year 0...yeah, it was probably broken then, too. It may have gotten broken when Doc entered "Dec 25 0000."
    • Of course there is a year zero, just not everyone calls it that. The number assigned to a year is an arbitrary convenience. It doesn't matter what label your calendar slaps on it, if the time machine knows to go back a certain number of years that's all that matters. Doc programmed his DeLorean with a different calendar than the common modified Gregorian— there are several calendars that use a zero year to mark the birth of Christ.
    • Maybe that's how Doc broke it — by setting it to zero.
  • Note: this theory presumes that the Telltale games didn't happen.
  • Leaving out the instances of people traveling back to where they belong (the various trips back to 1985) and the instances of people trying to fix something (all of the other trips the movies followed), the only time travel in the movies that was intentional were Doc's first trip to 2015 and Old Biff's trip to 1955. Doc probably just figured on thirty years being a nice round number for his trip forward, and Old Biff probably just went back to 1985 because that was the year he turned 18 (and - due to the events of the first movie - the date had a certain significance for him). There's no reason to think that the machine can't travel to other years.

The DeLorean LED readout is merely a relative measurement.
Going to 0000 from anywhen AD would result in landing in -1 AD/1 BC

Doc Brown is the Doctor.
He's an eccentric old man, he's more than happy to take an impulsive teenager on time travel journeys with him, and he understands enough about time travel to be very vigilant about preventing a Time Paradox. He's also enough of a pacifist that even when he knows the Libyan terrorists are coming after him, he's minimally armed and only wearing a Kevlar vest (which would do nothing if they aimed for his head). And at the end of Part 3, he's shown with two ten to twelve-year-old children but barely looks any older than he did in 1955, even though by his timeline he must have aged at least 40 years — Time Lord stuff!

Now, as for when in the Doctor's long and complicated timeline Doc Brown falls, it could be at any point when the Doctor spends a long period of time which the show doesn't account for (e.g. "Season 6B", a 200-year gap between Seasons 6 and 7, which would make him the Second Doctor). We would, though, have to account for the Doctor's incarnations in which he displays annoyance at people addressing him as "Doc", so it's not the First or Sixth Doctor. Or we haven't seen this particular incarnation yet. One theory suggests that it's at the end of a series of regenerations, in which the Doctor is just living out the rest of his years (but not the first set of twelve regenerations, as he's already gone through those and gotten a new set).

The Flux Capacitor doesn't make Time Travel itself possible, it makes it possible for a person.
The real function of the Flux Capacitor is to ensure that anyone traveling through time remains isolated from changes made to the time stream that may affect them. This is why Marty retains his memories from the "original" timeline and his Ripple Effect proof memory. Doc doesn't actually use the machine himself until the very end of the film and so his past was changed thanks to Future Marty's involvement while Marty remembers things the way the used to be. This is also why Marty fades from time so slowly. In reality he should be the first kid in his family to fade because if they never married and had Dave they sure as hell aren't going to have Marty, but Marty was shielded from time's effects due to the Flux Capacitor.
  • The name of the device supports this - flux is a rate of movement or current (in effect - change) and a capacitor temporarily stores energy. So the Flux Capacitor makes perfect sense for the name of a device that stores temporal changes instead of letting them flow freely.

At some point between reacting to the "new" 1985 and arriving in 2015, Marty's memories and personality change to fit the new version of history.
In the first movie, Marty has self-esteem issues so bad, he won't send his demo tape to a record producer in case they don't like it. Second-movie Marty automatically assumes he's going to be a famous rock star. This discrepancy is because second-movie Marty was influenced by a father who was a successful author, not one who never sent his book to a publisher for exactly the same reason Marty wouldn't send his demo tape. The new Marty's improved self-image has a downside, however: that sensitivity to being called "chicken."
  • This would also explain why Doc and Marty acted as though the new 1985 was the "correct" timeline throughout Part II. It just took a while for the Delayed Ripple Effect to get to Marty's memories.
  • It may also explain where Marty's weakness to the word "chicken" came from. Something may have happened exclusively in the new timeline to cause his disposition, explaining why this was absent from the first film.
    • To be fair, it was the correct timeline for Doc. Only Marty traveled back in time at that point.
    • Perhaps it's the same incident which made Needles his arch-nemesis who was never mentioned in the first film?
  • This is actually Fridge Brilliance, rather than Wild Mass Guessing. Otherwise, the "chicken" issue becomes something close to absurdity.
    • It also explains why the new 1985 is a good thing rather than the Fridge Horror of your family of 17 years having different personalities and histories—eventually, Marty acclimated to those changes as his new memories caught up.
  • Second-movie "1955" Marty is taking part in what appears to him as a Stable Time Loop. The ripple effect went round and round until it found an equilibrium.
  • This explains the discrepancy between the ending of the first movie and the beginning of the second. At the end of the first movie, Doc immediately tells Marty and Jennifer that they turn out just fine. At this point, Marty is still his old self, who doesn't have the problem with being called "chicken", doesn't give in to either of Needles' stupid dares, and doesn't get into an accident or get fired. By the time Part II comes around, the ripple effect has already caught up with Marty, rewriting his memories and personality, to the extent that he does all these things, leading Doc to hesitate before answering his question.

The McFly family is somewhat inbred.
Marty's paternal great-great-grandmother Maggie looks just like his mother because both are played by Lea Thompson. George and Lorraine are second cousins, although they are unaware of it.
  • Although it's possible that Mcfly men have a thing for women who look like lea thompson, also Martys great Grandmother looks like Lorraine too
Marty and the Doc are the same person.
The Doc never seems to age visibly; could he perhaps be an older (much older) version of Marty who has come across or invented some kind of rejuvenation treatment?
  • In Part III, Doc tells Marty a bit about his childhood, which would be pointless if they were the same person. Marty doesn't seem like the type of kid who would be enthralled by Jules Verne anyway. Furthermore, the Doc briefly touches on his family's history in the same movie, and he mentioned in the first film that it took his entire family fortune to build the time machine; therefore, he definitely has a background.
    • It is established in film continuity that Doc Brown is very against letting your earlier self become aware that you are their later self! He'd lie to Marty about their being the same person to preserve the universe.
    • We see the Jules Verne bits when he's with Clara. He has no reason to lie to her.
      • Women talk, man. Clara could accidentally let something slip to Marty. Either that, or Doc replaced his real memories as of being Marty McFly with false memories of a past as Emmett Brown to completely make himself a different person as seen below.
  • Doc is visibly younger in 1955 than in 1985 in the first movie. After going to the future, he got a rejuvenation that allowed Christopher Lloyd to play 1985-Doc without heavy age makeup. They also replaced his spleen and colon. In the first film, Christopher Lloyd wore old age makeup as 1985 Doc to make him look older, while the 1955 Doc was Lloyd without makeup, just as with the actors playing George, Lorraine, Biff, and Strickland, since for the majority of the first film, they were playing the 1955 versions of the characters, with the 1985 versions only appearing at the beginning and end of the film. However, for the sequels, Christopher Lloyd was predominately playing the 1985 Doc, with the 1955 Doc only appearing at the end of Part 2 and beginning of Part 3, so rather than have Lloyd wear old age makeup for the majority of the films, the writers wrote in the rejuvenation, in which Lloyd literally ripped off the old age makeup, so he could appear as is. Doc noticeably has more wrinkles before he takes off his disguise than after. Granted, at the end of Part 3 about ten years have passed for Doc, but maybe rejuvenation slows senescence.
  • Marty went further into the future to not only get a rejuvenation, but to have his brain genetically enhanced to make himself a genius— a side-effect was that it altered his personality. Before he went back and became Doc, he used his new intelligence to realize the damage he was doing to the timestream, and he had his memory erased or altered just before going back; he then remembered/"invented" the time machine.
  • Jossed by the Telltale games.

The Sims 3 is set in The Present Day (2008) version of Hill Valley.
Compare Hill Valley and The Sims 3
  • In The Sims, Sunset Valley/Pleasantview (the main setting of TS3 was founded by Gunther Goth, who is middle-aged in The Sims 3, the chronologicaly first game in the series. Hill Valley was founded in the year 1850 in BTTF, so that is impossible.
    • Sure, THAT'S what's impossible, in a shared universe in which physical time travel is possible via a sports car.
      • Does time travel invalidate mathematics somehow?

The time DeLorean is responsible for all life on Earth.
At some point, the time machine goes back to when Earth had just formed. Doc (or possibly Biff), unable to breathe, quickly returns to the human era, but leave behind some bacteria, which go on to evolve into everything else.
  • But it can't go back before year zero. There's no "BC/BCE" switch. And it can only do four-digit years anyway.
    • It can only display four-digit years and zeroes on the dashboard. Doesn't mean it can't actually travel that far.
    • Set the display to -4E9. Problem solved.
      • Still suffered from the Ontological Paradox.
      • Wait, you're saying we are all decendants of Biff?!
      • Well, there must be some reason why Humans Are Bastards.

From 1 BC to 1000 BC, the DeLorean just subtracts one from the absolute value of the year's number and adds a - in the first digit space.
Doc doesn't know ancient Egyptian, Greek, Babylonian, or any other language in its form from 999 BC or earlier, and he'd look as out of place there as he would in pre-White Man Cometh Aztec culture, and he really only cares about getting cool tech from the reasonably near future and going to the old west, so why bother putting an extra digit in just so you can risk giving a modern, virulent disease that we've adapted to to the direct ancestors of some tenth of humanity?
  • Alternately, the readout could just turn a different color when in the range of BCE years.

The future we live in now is the final result of all the time meddling through the three films.
The future of 2015 that Marty visited was only the result of the time continuum created by the events of the first movie. The results of the third movie are this time continuum we see today, so now, in 2010, there's no hope of hoverboards or flying cars or self-drying jackets or Mr. Fusion devices being developed in the next five years. Nice Job Breaking It, Hero!
  • This means that Marty and Doc are singlehandedly responsible for stopping the advent of hover tech, ubiquitous fax machines, holographic tech, home fusion reactors, flatscreen videophones, scene screens, robotic video waiters, food dehydration/rehydration, and Diana becoming Queen.
  • So Marty killed Diana?
  • This would ultimately result in paradoxes. The DeLorean would never have had a hover conversion, and Doc would have never saved Clara from certain death using the hoverboard. And we wouldn't see the flying train at the end of Part III. Meaning...
    • To be fair, Doc never specified that he'd taken the Time Train to 2015, only that he'd already been to "the future". Could be, he traveled into the future of our timeline well after 2015, by which point hover-conversion will indeed have been invented.

The BTTF universe takes place in a parallel universe to our own.
As far as we can tell, the real world and the BTTF world were pretty much identical pop culturally and technologically until at least 1985. Despite the open-endedness of Part III, Doc's train still has a hover conversion, and Jennifer still has that sheet of fax paper from 2015 (albeit a blank one, but bear with me), meaning that BTTF's 2015 still happens much of the same way, hover conversions and all (except that Marty is likely a successful musician).

It's just all in another universe. And we don't get hoverboards like they do.

That's not to say that BTTF's future is completely different from ours. Hover tech notwithstanding, perhaps BTTF's future is aware of things like House, Futurama, Harry Potter, the iPhone, and the Internet—all slightly different, of course, and all of which go unmentioned in the film for obvious reasons. (Heck, you could even argue that the likes of Lady Gaga or La Roux had a more lasting impact on the weird fashion sense of the BTTF future than in ours—just go watch the video for "Bulletproof" and compare the singer's look to some of the people in Part II.)

  • Confirmed in the comic book. Old Biff mentions having seen Jurassic Park, and Doc sees a Nirvana poster and uses the Internet (The Other Wiki, in fact) during his first visit to 2015.
  • Would this then suggest that our reality is the one where the Lybians got lost on their way to the twin pines mall, Doc went back in time but was immediately gunned down by a farmer, and the DeLorean was confiscated by the US government?

Speed for time travel is arbitrary based on the traveller's preferences.
For the first test at Twin Pines, Doc sets the speed for 88 mph to show off a bit to Marty ("...yer gonna see some serious shit!"); but the speed remains set at 88 when Marty accidentally jumps back to 1955. However, when Doc first departs for 2015 after dropping Marty off at the end of the film, the time machine definitely does NOT appear to be going 88, meaning Doc must have reset his temporal displacement activation speed (maybe as a safety precaution). That's what the the seemingly useless buttons and doodads on the DeLorean's ceiling are for, as Doc punches them at the end of Part I right before the car flies away. He sure didn't appear to be going 88 when he reentered 1985, and perhaps he reset it to 88 to be a showoff to Marty and Jennifer.

However, the arbitrary speed settings were damaged with the time control microchip when the car was struck by lightning in Part II. The replacement transistors and tubes from 1955 didn't have the speed settings that the microchip had, binding the time machine to the 88 mph needed for time travel, leading to the problem in Part III.note 

Word of God has it that the car jumped at the end of II because the shock wave from the lightning knocked it into a loop (hence the fiery trails looking like a double six).

Our timeline is the result of another time traveller messing with time.
Even though we already have some rudimentary form of flying car and hoverboard, by 2015 they will not be as advanced and ubiquitous as they were depicted to be in BTTF2. On the other hand, information technology marched much faster than what was shown in BTTF2, and pretty much every electronic device we have can be connected to the internet (which was implied not to exist in BTTF2). This is because another time traveller used his own time machine to change the timeline for his own purposes (just stealing the DeLorean for it would result in a time paradox, because it is equipped with technology from a future this action would cause not to exist). More precisely, he went back to 1989 and invented the World Wide Web as Tim Berners-Lee. This caused information technology to progress with unnatural speed, while at the same time slowing down to a crawl every other sector of technology.
  • Corollary to the previous WMG: if a BTTF4 ever gets made, this is what it will be about.
Doc, when he was in 2015 the first time, accidently interfered with the timeline
This caused Marty, Jr. and his sister to get in trouble and jailed. Think about it, Doc is FANATICALLY opposed to any tampering with time even if it does spare suffering. He won't reveal to Marty the nature of his "accident in the future", yet Doc seems DETERMINED to interfere with the future timeline and spare Marty's children any suffering.

Time-travelling has caused many alternate and canon timelines.
Meaning that every fanfic about the series can be true, including "Morty Mcfli"'s cameo in My Immortal.

During the build process, Doc replaced the DeLorean's stock engine
The stock DeLorean takes 10.6 seconds to get from 0 to 60 MPH, and 40 seconds plus a LOT of room to get up to 100. Doc had to include a lead-lined chamber for the plutonium, which must have added significantly to the car's weight. With the stock engine and that much extra bulk, it might not even have been able to reach 88 MPH at all. So he replaced it with a much more powerful engine from a sports car. That explains why the engine noises don't match those from a normal DeLorean.

Sonic CD is an alternate timeline of the original Back to the Future
After Marty went into the future and never came back, Doc decided he would rather escape than risk being arrested for life. He creates a spaceship (hey, he built a time machine, so how come he couldn't manage that?) and just so happens to crash into the Past version of Little Planet as he's passing over Mobius. He develops new and fantastic inventions in his laboratory (Wacky Workbench), including a version of the time machine that can operate at lower speeds and without need of a car to do it. A long while after Doc died, Robotnik found Doc's stockpile of time machines in Wacky Workbench (in the present) and decided to use them to take over Little Planet. That secret statue in Wacky Workbench Past that gives you rings? It's Doc's grave.

Needles is Biff's estranged son.
Because come on, every Tannen has a beef with a McFly in every timeline EXCEPT the present one. Needles is just Biff's son from a woman that's no longer with Biff. So he has a different last name and doesn't associate with his Father until he has a son of his own, which he names Griff as a nod to his Father that he accepts him into his family.
  • Potentially Jossed by the game - Edna Strickland (the Vice Principal's busybody sister) yells at Biff's daughter Tiff.
    • Jossed further in Episode 4 by a reference to Mr. Needleman (probably Needles' grandfather), whose mind map suggests him becoming a hooligan.
      • Unless Needles was born out of wedlock and Needleman is his mother's surname.
      • The video call information in 2015 gives his full name as Douglas J. Needles, so it’s not a nickname. That being said, another line in the game mentions a Frankie Needles, so maybe he’s Needles’ grandfather instead.

Jennifer looking different in Part 2 and 3 is a side effect of the timeline getting changed around.
While Marty's parents presumably conceived their children at the same or similar time as the previous timeline, Jennifer's parents conceived her at a different point, resulting in the egg being fertilized by a different sperm; the child was still female but looked different.

Marty is very vain about his teeth.
He refuses to eat anything with sugar and in 1885, members of Mad Dog's gang mentions that he never saw teeth that white and straight that weren't "store bought". Could be Marty had braces when he was younger and now prides himself on having very nice teeth.
  • The refusing to eat sugar could be typical teenager watching his weight, hence why he's drinking Tab in 1985 and asks for Pepsi Free in 1955. And in the late 1800s quality dental care was unheard of, so the gang member's comment is meant to be an aversion of Eternally Pearly-White Teeth.
    • Alternately...

Marty has mild type II diabetes.

His family circa 1985-A can't afford to treat it/their insurance won't cover it, so he has to be extremely careful to avoid sugar (which he does) and get lots of regular exercise (considering how much running/jumping/skateboarding, etc, he keeps up on that too) in order to hold off the need for insulin and lower the chances of complications. In 1985-B, his family is simply better off and could afford better medical care for him to begin with, so he's less concerned about his diet (Hence being totally cool with eating a rabbit full of buckshot).

  • But when Marty is seen talking to George the day after he breaks into his house disguised as "Darth Vader from Planet Vulcan", he's seen drinking regular Pepsi, which has sugar in it.
    • Maybe Doc found out Marty had diabetes, and keeps insulin around the lab just in case, and there's some in the glove box of the DeLorean.
    • And consider how much "walking" he has to do going around 1955 Hill Valley , he probably can handle some sugar.(as long as it's not too much)

Marty was always sensitive to being called "chicken".
He was just never called it in the first film.
  • Although when Lorraine accused him of being "square" for objecting to her drinking he took a drink from the liquor, so that could be a very subtle example.
  • And bearing in mind that he saw George as a complete wimp in the first timeline - being called "chicken" meant being compared to his father.

The Bttf Trilogy represents the themes of the first three Metal Gear Solid games.
  • The main theme of the first installment of each trilogy is GENE. The impetus for most of Marty's actions in the first movie is to cause his parents to marry once again, causing him to come into existence from their genes. Likewise, the second movie matches with Metal Gear Solid 2: Sons of Liberty's main theme of MEME. The consequences of information from the future traveling backwards are expanded upon and shown in detail, as Biff uses the Sports Almanac to change his past and eventually 1985. Finally, the third movie fits with Metal Gear Solid 3: Snake Eater's main theme of SCENE, since it puts the main characters in a completely different setting than any of the movies offered, and shows how that affects the other characters' outlooks. It's also like the third game in that it shows familiar character-analogues and recurring series events in a historically earlier context.

Certain aspects of time itself is sentient and can affect timelines, and it likes both Martin and Doc.
  • The reason Marty and Doc have time traveled several times without screwing up enough to make any fatal paradoxes is because the sentient parts of time has grown to like them both, and cleans up parts of time to help them out. The fact that the McFly family suddenly becomes awesome, and that Doc eventually found the love of his life, was little gifts from time itself. And the reason they often get into trouble (lightning bolt hitting the DeLorean much? Biff going back in time?) is time wanting to get them into adventures both for its own amusement and them getting amazing memories.

The DeLorean is destroyed/wrecked in every third installment.
  • This is more of a weird idea I had. Concider. "Back to the Future Part III"? The DeLorean was destroyed by the train. "Citizen Brown", the third episode of the Telltale game? The DeLorean A) crashed through a billboard, apparently getting wrecked (pointing your cursor over it at the start of the game has it labeled "Wrecked DeLorean", B) had it's window broken and C) fell from said billboard, and crashed into the ground! Now, maybe it's just me, but I smell something fishy here...
    • Which leads to the obvious corollary, or whatever: The fourth installment sees the restoration of the DeLorean. The obvious examples are:

The components in the hoverboard could be refitted into a crude time machine
It's among their assets.
  • Jossed by the Telltale game, unless they bought a new pink Mattel hoverboard in the future for some reason.

Doc Brown was named after himself.
The Doc's parents, a young couple new to America in the 1880s, changed their last name to Brown after meeting an inspirational and quirky blacksmith, and subsequently named their son Emmett after the blacksmith and encouraged him in scientific pursuits.
  • As stated in the movie, the Browns didn't come to Hill Valley until 1908, well after Marty and even Doc left the old west.
  • And according to the Telltale games, Doc's father was very much against young Emmett's interest in science and wanted him to go into law instead.

The reason why Doc is so cheerful despite everything
He has a goddamn time machine. His second order of business when Marty got back from 1955 was to retroactively cause all his enemies not to exist.

Doc is a fan of Carl Sagan because Carl succeeded where he had failed.
Carl Sagan's deservingness of his fame is something of a point of contention among the scientific community because of how little he has actually contributed to science. However, his immense skill in getting people interested in science and in providing perspective and aiding in understanding is indisputable. Compare with Doc, whose only admirers were a teenage kid who broke into his garage and that kid's father, who only respected Doc because his son did.

This could potentially explain one of Doc's strangest choices...

Carl Sagan's Cosmos inspired Doc to choose a DeLorean.
When the time came to put his flux capacitor into a vehicle, he realized that if anyone was ever going to take him seriously - something that had rarely happened for him - he'd have to capture their imaginations, just as Carl Sagan had with his TV series and its cool 'ship of the mind'. He waved off his own concerns about his integrity with what he believed also occurred to the people behind the show: you might as well do it with some style!

Doc Brown and his family started the race of Time Lords.
It's possible Jules and Verne were affected in some way by the constant time travel, and that frequent exposure to the time stream integrated new powers to the DNA of the Brown clan. As centuries passed, the descendents of Doc Brown made more time machines, eventually integrating space-faring capabilities into the machines. This new breed of humans decide to leave Earth at some point, and found their own, free and open society on a planet called Gallifrey. Down the line, a young man of a race known as Time Lords is visiting 20th century England and gets an idea for a ship design...

The events of the movies are directly responsible for the events of Puella Magi Madoka Magica.

Marty's drag-racing crash in in the original timeline would've killed the father of Hitomi Shizuki when he was still a boy visiting Issei (first generation Japanese-American) relatives in Hill Valley. Hitomi of course becomes the Unwitting Instigator of Doom for Sayaka's (and the show's) Start of Darkness. But the Ripple Effect created when Marty avoided the crash caused the crash 26 years later that injured Sayaka's love interest's (also a budding musician) wrist, and eventually leads to her contract (and eventual Witchdom...which of course sets off a Domino Effect that destroys the world in one timeline). All their messing around with the space-time continuum had of course put considerable strain on it.

Of course in the previous version where Marty does crash, Marleen becomes a Magical Girl to help her struggling family and deeply depressed father...and eventually a Witch when she's arrested trying to bust out Marty Jr. in Timeline 1a and when Marty gets fired in Timeline 1b. One of the survivors of the crash (Hitomi's would've-been second cousin) became Marty's boss at his office job, initially forgiving and taking pity on him, but nursing a deep grudge that led to Marty's firing.

Before the time machine was invented, Marty was also rather unconfident (he didn't think anyone would like his audition tape), and wouldn't have gotten in that drag race in the first place. But as mentioned above, changing the past the first time around also made him rather more cocky and reckless.

I also wish Doc had never invented that infernal time machine...

Hill Valley was originally named after its founder.

A man with the family name of Hill. They stopped calling it Hill's Valley after awhile out of laziness.

  • This is explicitly mentioned in Number Two, the first version of the script for the second movie. There's a scene in 2015 where Marty passes by a statue portraying "William Hill, founder of Hill Valley".

Doc is also responsible for creating his own family's original fortune.
Doc's family, the Von Brauns, moved to Hill Valley in 1908. Assuming that Doc Brown in 1955 was the same age as Christopher Lloyd at the time (47), then Doc was born that same year. At some point, Doc travelled to meet his parents in the past and inspired them to move to Hill Valley, giving them valuable information about possible business or investment opportunities, allowing them to make the money that he would later use to build the time machine.

There is a God of Karma in the BttF Universe.
In the pre-movie version of the timeline, the Tannens have been giving Hill Valley a hard time (Mad-Dog the murderer, Biff the wanna-be rapist, to name two examples) for a hundred years or more. The GoK finally got fed up and used a pair of fairly decent chaps and their time machine to put the Tannen family through a Humiliation Conga, while rewarding Doc and Marty with better lives than those with which they started (Marty's family escaped loserdom, Doc got a family). Not Laser-Guided Karma, but definitely heat-seeking. Bonus sub-Guess:
  • "Red" Thomas was corrupt as Mayor.
    • He got on the GoK's bad side, too, which is why the Mayor in 1955 is a bum in 1985.

There will be another sequel.
With 2015 fast approaching and Michael J. Fox's return to acting, the timing's right...It'll include such things as a Lampshade Hanging of "jigowatts" and how Part II saw 2015.
  • A sequel coming out in 2015 is Jossed.

Due to the delayed feedback effect in the movies and the butterfly effect from real life, Marty's actions in the first movie changed Jennifer's genetic makeup.

That's why she starts off as Claudia Wells in the first movie and has suddenly transformed to Elisabeth Shue by Part II. (Of course it doesn't explain the fact the same scene has played out twice in the subsequent movies with both actresses.)

  • If that's the case, why does Marty recognize her as Jennifer? He clearly has no memories of the new timeline given how shocked he was at seeing his family and house.


There is a missing movie between Parts I and II.

Originally, the second film was going to take Marty to the year 1967. Perhaps his meddling with events of that year causes Jennifer Parker to have the same father but a different mother. Marty goes back to 1985 after these events and the first scene of Part II happens a little later than it did at the end of Part I. Doc returns from the future after finding out that bad things still happen to Marty's kids, and the rest of the film takes place.

After Doc made his train time machine, he wrote the almanac.
He ensured that the race that Old Biff used to convince young Biff that it worked, but made sure the rest of it was completely wrong. Just in case, that way even if Biff got a hold of a time machine again, he would fail.
  • That wouldn't have helped much, as one doesn't need the whole almanac to make a killing; just the highly improbable bets. Old Biff could have set it up so he told Young Biff to mark anything that would yield more than a 100-1 win (e.g. Cubs winning the World Series 2015), and then given that list that he compiled to Young Biff, so he could bet and win.

Marty returning to Doc at the end of Bttf2 and the start of Bttf3 directly influenced his decision to put the ripped up letter of his death back together.
Throughout the majority of the first movie, Doc was adamant on not knowing what his future holds and rips up the letter explaining his death even as Marty pleads that his life depended on it.However, fast forward to the start of the third movie and Doc has to once again help Marty out. During this brief time they have stumbled on his future self's grave, who had been killed in 1885 by Mad Dog Tannen. Marty now is adamant on saving Doc in 1885. My opinion is that 1955 Doc was touched by Marty's commitment on saving him. This, coupled with the fact that he now has knowledge that he will die at some point during this whole ordeal, which means that he knows too much about his future anyway, means that indeed regarding the letter Marty wrote, 'what the hell'.
  • Except he also did it in the timeline created at the end of BTTF1, where Marty did not "yet" return to 1955 to stop old Biff, and consequently, Doc never interacted with Marty again until Marty grew up in his proper time.

Doc got the idea for the bulletproof vest from Marty.
He checked the historical records of the time where future Doc in the past should have died, and found out that a duel between Marty and Mad Dog Tannen instead occurred. The impressed locals likely recorded quite a few details, including the bulletproof vest.
  • Jossed by Bob Gale. During an interview about the game, he said that in the series, the effects of a time jump are never shown before showing the time jump itself. Meaning that LP Doc used a bulletproof vest despite living in a timeline where the events with Marty and Doc in 1885 never happened.
  • While he could have avoided being shot entirely once he read Marty's note (by sabotaging the Libyans somehow, for instance, or finding another source of plutonium), it would have created a paradox - if Marty didn't see him get shot, he'd have no reason to write the note (or accidentally travel to 1955, for that matter) in the first place. Doc is too concerned about damaging the fabric of space-time to ignore a paradox of that magnitude - the only way he could survive without risking tearing the universe inside out would be by letting Marty believe the Libyans killed him long enough for Marty to travel back in time. If Marty's note mentioned that he'd been shot in the chest, he knew a bulletproof vest that could handle their ordnance would do it. He may have also managed to contrive a method of swapping their ammunition with blanks (to minimize the risk of bullet fragments from hitting something exposed or some minor change making the Libyans pull off a head shot this time around), in which case the vest was a backup in case they noticed or used different weapons than he expected.

The Flux Capacitor is a Stable Time Loop
Some time after BttF1, Doc obtains the device which sends people to sleep and causes short term memory loss, with those it's used on often attributing memories to dreams. He also damages the DeLorean, the flux capacitor needing repair. As Doc doesn't trust himself to tamper with such a volatile component by himself, and knowing that no one else on the planet knows how it works, he travels back to a past version of himself. To prevent the timeline being disrupted, he wipes their memory afterwards, but they retain some of the memories... Leading to the idea for the Flux Capacitor and how it works coming to Doc Brown in a dream.

The Michael J. Fox Show is Marty's new future.

In a new timeline, Marty's music career did not take off and Jennifer left him. He changed his name to Mike Henry and moved to New York, where he had a new wife and kids who do not look exactly like him. There will be an episode that takes place October 21, 2015.

Everything before Marty wakes up at the end of Back to the Future is a dream.
Marty was merely surprised about how different his family and Biff were because his dream of going back to 1955 was so convincing. In fact, it was so convincing that he imagined what might have happened afterward.

Everything after Marty goes to bed at the end of Back to the Future is a dream.
He did go back in time to 1955, but his family life was not drastically different from the original timeline. He also dreamed of the sequels, in which Jennifer's physical appearance is inconsistent.

Marty imagined Doc.
Neither Marty's parents nor his siblings acknowledge Doc Brown. He imagined him because he was so bored with his life.
  • Except that Strickland acknowledges Doc talks about him like he's a real person.

Doc Brown is Professor Plum.
In 1955, after the events of the Clue movie, Professor Plum got a new identity and chose a last name that also referred to a color. He even made up an entire family history for himself.
  • Or Doc Brown is his real name.

George McFly created Star Trek and Star Wars.
What if Marty McFly was careful about making sure that he does not mention things from the future to his father? There is no concrete evidence to suggest that Star Trek and Star Wars even existed in the original timeline. After Marty scared George into getting together with Lorraine, George decided to pursue a career in science fiction. At first, he tried to publish A Match Made in Space with mentions of "Darth Vader" and "the planet Vulcan." However, publishers were not interested right away, which is why it was not published until 1985, 30 years after Marty gave him the idea. He decided to shelve the book and pitch his science fiction ideas for television. As it turned out, some of the stories that George had written in high school that he did not want Marty to read were the basis for Star Trek. He pitched the idea for the TV series and it became a hit. Since it seemed that his book would never be published, he went ahead and named a planet "Vulcan" and included the hand gesture that would be used by Vulcans. When Star Trek went off the air, he turned toward a career in film. As an alternate universe George Lucas, he wrote various drafts of the script for Star Wars and named a character "Darth Vader." After finishing the original trilogy, George once again showed publishers A Match Made in Space. Since his name was more well known by that time, they agreed to publish it. Since he had already referenced Vulcans and Darth Vader in his previous works, he had to change the names to make it clear that this was a separate story. The book went on to spawn a series of its own.

Needles had called Marty a chicken all of his life.
Marty's need to disprove claims that he is a chicken is a result of a Noodle Incident. Or should I say Needles Incident?


Marty was first called "chicken" in the second timeline.
After changing history in the first film, Marty ended up in a timeline in which he obtained memories of being called chicken all of his life, something that had not happened in the original timeline. Perhaps the now brave George McFly ended up being dickish enough to call Marty a chicken whenever he was afraid to do something in the second timeline.
  • It's not so much that his memories or personality rippled, it's that deep down Marty was always a self assured jerk to the point of arrogance but he grew up afraid to take a chance. After time traveling, not only did he now feel like a bad ass, seeing his new future where he grows up wealthy and happy flips a psychological switch in him, bringing out that aspect of his personality.

(This applies for time travel in general) People born BEFORE a temporal incursion DO notice the changes in the timeline.
So for example everyone born before 1985 would notice the changes occur around them. However no 'sane' person would understand what just happened. This leads to many neurosis, and mental illness'. Your grandpa doesn't have alzheimers, it's that originally things were different and he remembers that original timeline. Conspiracy theorists begin to crop up because they noticed things changed around them and can't explain it. Paranoids are remembering old enmities and conflicts that no longer exist in the changed timeline. Also, humans would have perfect memory and recall EXCEPT the temporal incursions keep changing things so memory seems inaccurate, you look at a picture and notice you're wearing a blue dress in it when you remembered it being an orange dress...because IT WAS, up until Doc and Marty, or the Doctor, or the crew of the Enterprise or the Time Traveler's Wife's husband went back in time and caused a temporal incursion. History books aren't innacurate, history has changed since they were written. There is no ripple effect on memory, we all notice the changes and without time travel humans would be more mentally stable, have perfect memory recall and all history books would perfectly accurate.
  • Based on this and the fact Marty stayed in 1955 for a whole week before returning to the very same day he left, it took exactly one week after Marty's return before George, Lorraine and Biff to remember how their lives used to be before Marty messed with their past. Remembering a former life as a white-collar worker who made a living by taking credit for George's work must have compounded 2015 Biff's bitterness. He probably also figured out Doc's Time Machine is the reason his life changed and decided his own attempt to change his past would be a case of "two wrongs make a right", or "left" if nobody corrected him on that specific saying. Upon checking records of his life prior to 1985, Biff figured out when his life became different from what he remembers and it was no mere coincidence that his 2015 self went to the day of the dance that made George and Lorraine a couple.

Doc Brown is a relative of Peri Brown from Doctor Who.
Emmett Brown is Peri Brown's great-uncle. Peri met The Doctor in 1984. Sometime during her travels, she returned and told Doc about her adventures through time and space. This inspired Doc to get back to making a time machine, which he did in 1985.

You can never 'fix' a timeline and there are no parallel ones either
BTF Rodenberrian physics shows that there are no parallel time lines, or else there would be no fading picture. Each time you travel back in time it overwrites the future from that point. However despite what they think they did, you cannot restore a timeline. You can only overwrite an overwritten timeline with one that resembles your original timeline close enough.

Marty is the reason that "heavy" became slang for something serious.
It's noted with a similar meaning on sites about slang in the 60s. In the original timeline it may have started in the '80s, but Marty introduced it early - it just took a little time for it to become common slang outside of Hill Valley.

How the flux capacitor works...
It temporariliy stores a large amount of electrical energy as a conventional capacitor does, then discharges it as gravitational energy, possibly somehow generating exotic matter. Basically creating a wormhole big enough and lasting long enough to transport a DeLorean-sized object travelling at 88mph through time.

88mph is significant.
Following on from the previous WMG, it's not random but is the speed at which the DeLorean must travel to get through the wormhole generated by the time circuits before it naturally collapses. Doc Brown calculated it as the necessary speed based on the length of the car and the projected time the wormhole would stay open.

Marty would become a famous rock star in the original timeline.
One of his bandmates or his girlfriend would send a demo tape behind his back or he'd be told of how a similar fear of rejection was what made a loser out of his Dad. Also, Needles wouldn't have dared a carless person to that race so Marty wouldn't have suffered the accident that ruined his career in the future shown in the second movie.

Biff would have a Karmic Death in the original timeline.
That timeline's Biff is established to be a drunk driver in 1985. Had his past not been changed, he'd have died in a car crash he caused between 1985 and 2015.

Marty's memory is immune to Ripple Effect even when the effect is caused by changes he's not involved with.
Doc states that people who are outside their time when history is changed don't have their memories altered to fit the new reality. When Marty returns from his first travel to 1955, he returns to the same day he left despite having spent one week in 1955. That means he's one week behind his own time and thus his memory won't be altered by the consequences of time travels done without him.

Changes to the timeline only ripple forwards

I may be overthinking things here, but it is in my nature.

This might seem like an obvious statement, because changes in the past should only progress forward linearly, but it has implications for time travelers. Essentially, changes to the timeline do not affect time travelers further back in the past. Objects (such as newspapers, matchbooks or photograps) and people from the future will change as history is altered but (as is seen in the movie) the changes only occur after interference in the past.

First, consider the implications of the 1985A of Part 2. With the Doc of that timeline institutionalized, the Marty of the timeline (supposedly in Switzerland) is unlikely to have taken accidental trip back to 1955 (and he would certainly have no flyer soliciting donations to save a clock tower that no longer exists). Nonetheless, when Marty and Doc go back to 1955, the Part 1 Marty is still there and going through the same events as in the first movie. This might seem like a paradox, but it makes perfect sense if changes to the timeline only go forward: Biff did not change history until November 12, so Marty's arrival on November 5 and all of the events that followed remain part of the past. This also means that, if asked, that Marty would always report that his father is a wimp and that Biff trashed the car; the change to his parents' histories did not change until after his arrival, so he would always remember his original history.

Note that the original Marty's continued existence after Biff's book delivery can be attributed to a Delayed Ripple Effect.

Based upon this hypothesis, Biff could have retroactively prevented Marty's first trip through time if he had given himself the book some time before November 5, 1955. Doing so would have allowed the timeline changes that his actions created to reach November 5, thus erasing Marty's trip from history altogether. Since he chose November 12, though, the changes that he made could not ripple "back" to November 5, preserving Marty's presence in that past.

This also explains why Doc in 1885 does not know of his impending murder by Buford Tannen despite his younger self learning of the event in 1955. When he was accidentally sent to the past, his younger self knew nothing of those events. If changes to the timeline only move forward, the Doc of 1885 would only know of his history as it was before he was sent back in time; he would not be aware of any changes that were made after he left 1955. Possibly, Doc's memories were adjusted once he traveled to some point after 1955.

I admit that this is not a perfect explanation, as it does raise some questions.

That theory being true proves Doc right when he told Marty that going back to 2015 to prevent Old Biff from stealing the Almanac and the Time Machine wouldn't undo the harm he caused by doing so.

One question: If asked before his time travel adventures, the Marty of the post-BTTF1 1985 would probably report that his parents are successful and that Biff runs an auto detailing company; what would happen, then, if a time traveler stowed away in the DeLorean on the night of Marty's first trip through time and then, once in 1955, asked Marty about his parents? Based upon my above hypothesis that the Marty in 1955 is always the same, this would create complications. Still, an argument could be made that stowing away in the DeLorean itself changes history as of 06:00 on November 5, 1955 and thus it could update the Marty of that time. On the other hand, it could create a Time Crash.

Marty being called chicken
comes from the general habit of Tannens to taunt their opponents into attacking them, as evident in all three films. While in the original timeline no McFly ever stood up to a Tannen and therefore the insult was unknown to the McFlys. However, once George started to take a stance against Biff, the latter took to goading him into further fights. The new, self-conscious George would not have it, therefore would beat Biff up each time (did you really believe Biff gave up after one lucky punch?) and then raise his son with the same Berserk Button ("Don't let them call you chicken, son.")

There's a delay in an action taking effect on future events
This is ignoring the Telltale series and is mainly there to explain how Doc and Marty got back to 1985 in Part 2 after old Biff gave 1955 Biff the almanac. More than once, we see a ripple take place that doesn't necessarily make sense with what's happening in the film.In Part 1, Marty is still collapsing until Lorraine and George kiss on the dance floor, but Lorraine was already smitten with George and it's unlikely she was willing to give up on him that quickly after he saved her from Biff. At a guess, when Marty gets back to 1985 (that he's unaware he's altered) where George is a successful writer and Biff works at an auto detailing service, it doesn't change until between when he gets there and when he wakes up the next morning.In Part 2, the newspaper and the matchbook don't change until Marty burns the almanac, which implies that Biff would have gotten it back and the Bad 1985 would still have existed until he burned it. Which makes no sense at all, as Biff had no idea where they were, didn't have a working car, and had no way of tracking down one punk kid and a crazy old scientist with a flying car when he didn't even have a real name on either of them. The timeline had already started to change from Marty getting away from Biff after the incident at the tunnel.In Part 3, the "YOU'RE FIRED" fax doesn't erase itself until after Marty avoids the accident, but he clearly wasn't planning on racing Needles for real even before then, having arrived back in 1985 with a newfound confidence and the ability to shrug off being called chicken.Reality has a delay before it sorts itself out with a new timeline, letting Old Biff get back to 2015 before the ripple took effect and letting Doc and Marty get back to 1985, which by then had already changed.

Biff's gang member Match is the grandson of Caledon Hockley.
Both are played by Billy Zane and a deleted scene from Titanic mentions that Cal had children. Perhaps after his family lost their money in the Great Depression, one of his kids moved out west to California to find new opportunities and started a family there.

Doc Brown became an entrepreneur in the past.
Given his knack for inventing and creating machines, plus the considerable expense of re-creating a time machine from scratch with technology you would have to create from scratch right down to the basic components (no vacuum tubes even before the 1900s and no way Jules or Verne are even in their mid teens in the ending scene, so the family as we see them must come from the 1890s), it's hardly suprising and indeed necessary. Being a blacksmith in a whistle-stop town is hardly likely to generate that kind of income. Most likely he put his skills to work and started developing products and grew a manufacturing business out of it, which helped the nascent economy of Hill Valley on its way, whilst being careful to avoid inventing (or "inventing") anything too out-of-period for the time that could be commercially exploited.

George was supposed to be left-handed.
Forcing a naturally left-handed child to use his or her right hand, as was commonly done in former generations, can seriously damage the nervous system. That's why George was quirky. He was traumatized from the experience, and was turned into a wimp because of the browbeating. As a teenager, he eats and writes with his right hand, because that's what was drilled into him, but the punch he threw with his right hand clearly failed. Enter the left, which did the trick.

The Big Bad of the next IDW arc, "Hard Time", is Needles
At this current moment, the Publisher's Summaries for the first three issues are out. From that, the following is clear: someone is after Marty, his childhood memories are starting to not match the present, and issue #3's summary strongly hints at someone altering the pastnote .

Now, keep in mind, "Needle's Story" (the issue that came out before this series and detailed Needles meeting Marty in 1979) ended on Needles in jail, telling Marty that he's coming after him once he gets out. Call me nutty, but I seriously think Needles, once out, is going to stumble across a time machine, most likely the DeLorean, go back to 1979, and go after Marty then. The plot of "Hard Time" most likely is about the repercussions of Needles altering Marty's past.

Doc's plan with taking Marty to the Future
  • I've long had the following theory about the events of the sequels: I think Doc's main goal in bringing Marty to 2015 with him wasn't to rescue his children from disaster but to teach Marty a lesson about the consequences of peer pressure, hoping that it would scare him into avoiding the accident that ruined his future. Consider the following:

    1. At the end of the third film we learn that the pivotal accident was set to occur later the same day from the point Doc whisked Marty and Jennifer to the future at the beginning of the second film. That's why he was so frantic that they should come with him immediately (and not, say, wait at least a few months to recuperate from their previous adventure): he was trying desperately to get Marty away from the disastrous event, so that at least he'd have some extra time.

    2. It's heavily implied that Doc knew about the accident the entire time, but chose not to tell Marty. When Marty asks Doc "Do we become assholes or something?" Doc hesitates for a moment then nervously says "No no no no, you and Jennifer turn out fine." This is a a subtle difference with the way the scene was filmed in the first movie (when the creators reportedly had not yet planned for sequels). In the first film, he sounds utterly sincere when he speaks that line. In the reenactment of the scene at the beginning of the second film, he sounds like he's hiding something.

    3. Why didn't he tell Marty straight out about the accident? He explains it during the scene from the third film where he's arguing with Marty about his decision to duel Buford, and he blurts out about the accident, before stopping himself and commenting, "I can't tell you. It might make things worse." If Marty finds out about it, Doc reasons, he might manage to avoid that particular catastrophe. But his bad habit of submitting to dangerous dares would remain, and with the future thrown into flux, for all Doc knows something worse might happen than the accident—he might even end up dead. Doc decides that his only hope of preventing the accident or anything comparably terrible that Marty might do to himself is to get him to grow out of his bad habit. That's what ultimately ends up happening by the end of the third film, albeit not quite in the way Doc anticipated.

The DeLorean—the base unmodified vehicle itself—is a vastly different car than the one in our universe
Besides the engine's sound being different from the real one in our world, Doc briefly comments on the car's "stainless steel construction". DeLoreans weren't constructed entirely of stainless steel. The stainless steel body panels and full stainless steel doors were attached to a fiberglass tub that sat on top of a steel backbone chassis (they tried to make the chassis stainless steel but couldn't make it feasible at the time). Given Doc's familiarity with the car and attention to detail, he should've said "the stainless steel body panels made the flux dispersal". In fact, the differences in body panels (notably the front hood or bonnet) between different model years was due to the problems working with stainless steel. Therefore BTTF's universe version of the DeLorean is a more technologically advanced and faster car than our version. Stainless steel is heavier than fiberglass and being able to build a car out of that material would've been tricky and very expensive at the time (not to mention heavy) unless there was some major advancements in metallurgy and manufacturing techniques. In other words, John DeLorean's dream cranked up to eleven.
  • On the other hand, to save weight and cost, there's no reason not to make the passenger compartment/engine bay tub out of composite materials. It would also make it easier for Doc to electrically isolate the car's electrical system and prevent it interfering with the time machine functions.

The reason why the DeLorean time machine cuts off at times is that they are in close proximity to other DeLorean time machines.
Now, no one ever questioned why the DeLorean's engine in the first film cut off as Marty attempts to head back to 1985 from 1955, or why it cuts off again when he gets there. There is a possibility: the DeLorean time machine gets "interference" (the best word I can think of to describe it) from other DeLorean time machines. Think about this: When Marty attempts to head back to 1985, he gets into place and everything is set. Then the engine cuts off. Maybe the reason why is that at that same moment in time, the future DeLorean (as seen in Back To The Future Part 2) gets struck by lightning and is sent back in time to 1885. Somehow, when the DeLorean travels, it emits something that interferes with the engine of other nearby time-traveling DeLoreans. And it takes time for this interference to dissipate (which explains how Marty was able to start the engine again only a few minutes after it cut off). When he gets back to 1985, it is at 1:24, three minutes after the DeLorean's first time jump. This is what causes the DeLorean to conk out again shortly after arriving, because whatever the interference that was generated by the previous DeLorean's time jump was still in the area and hadn't completely dissipated when the Lybians drove by. The only time that one DeLorean time machine doesn't affect any other is the one from 1885 residing inside of the cave that Doc put in there in 1885.

Marty's personality doesn't change with the rest of his family because of his friendship with Doc.
Because Doc doesn't give a shit about what anybody else has to say about how he lives his life. He's a scientist and he's doing science, and if he wants to wear goofy shirts and live adjacent to some Burger King dumpsters, then that's goddamn well what he's gonna do. Doc Brown ain't a democracy, bro! With Doc always treating him as a friend and an equal, Marty is able to recognize the value of being true to oneself and becomes a much more self-actualized person as a result, regardless of the surrounding circumstances.

The only major difference is that in the Twin Pines timeline, he doesn't relate to his crappy family and has learned not to depend on them more than he has to, while in the Lone Pine timeline, he's confident in himself, but he's also under a lot of pressure to succeed the way his dad did. Since his dad famously refused to back down from a fight, Lone Pine Marty becomes oversensitive to accusations of cowardice because he's trying to live up to George's example.

The most of franchise is canon.
That' right, the films, the comics, the animated series and Telltale video game are all canon and on the same timeline. I'll explain.

Obviously, the films are all canon to one another. The some of the recent comic series by IDW fills in some of the gaps in the timeline (such as how Doc and Marty "meet" originally in the 1980s) and even adapts the story of the Telltale game for the storyline "Citizen Brown", which Bob Gale had a hand in for creating and himself considers it as a "Part IV." Now, you're probably thinking, "Where does the animated series fit in? And how?" Well, at the end of the game, Doc and Clara maintain a part-time residence in Hill Valley in 1986. And we know that Doc and Marty still have the DeLorean, and Doc clearly must have the Time Train stashed somewhere whenever he's staying in 1986. And seeing both are intact, and that Doc and his family has a residence in Hill Valley, that could set up the animated series. After the ending to where they jump to whenever, Doc and Marty come back and eventually, Doc and Clara decide to relocate closer to where Doc has the Time Train stashed, and have a bigger plot of land for Jules and Verne to play on and a bigger garage for Doc to perform experiments in. Of course, this allows Doc to be able to update the DeLorean several times and gives it features that could come in handy.

Yeah, there's a lot of holes in the idea, but it does present an intersting scenario.

  • Also, this can explain the existence of The Institute of Future Technology in the BTTF ride, as Doc continued with his time travel experiments and inventing items after the events of 1986, leading to the foundation of the Institute.
  • Additionally, any inconsistencies or contradictions between the different works could be explained as future time travel slightly altering the past.

The franchise will receive a semi-Continuity Reboot not unlike Star Trek (2009) or Mortal Kombat 9
A new Back to the Future trilogy will star an alternate Marty McFly and Doc Brown who are respectively student and teacher at Hill Valley Community College who discover parallel timelines instead of time travel, bringing them into contact with the Marty, Doc and Hill Valley we know.

Doc Brown is part toon, and is related to Judge Doom from "Who Framed Roger Rabbit".
Doc has a toon-like reaction to alcohol, and has a twin who is the most human-like toon we see in WFRR. Judge Doom's name in the expanded universe is Baron von Rotton, and Doc's ancestors were the von Brauns in Germany. Let's say that they're both branches of an even bigger German "toon" family from the 19th century, who intermarried with humans and left Germany in the early 20th century. The von Rotten branch retained more aspects of tooniness, but the von Brauns were basically squibs who tried to completely assimilate to human society. Except for a certain eccentric demeanor and an aversion to alcohol!

Hill Valley is an SCP, if a mostly self-containing one. Doc himself is an employee of the Foundation
  • Hill Valley has a memetic effect that makes it very difficult to leave the city, which is why several generations of the same family have remained there for centuries.
  • Biff's actions in Part 2 constituted a containment breach, which is why Doc was so adamant about Marty retreiving the Almanac.

Doc has Asperger's Syndrome
  • It's never stated but he seems to possess the symptoms of it. He's socially awkward. He is a genius in a particular subject. He is misunderstood by the town. Doc is an undiagnosed Aspie.

The DeLorean has the ability to undo the last trip.
It's a functionality that's a part of the "Last Time Departed" display. Ordinarily, one would think that it's just a reference allowing you to quickly make a second trip that's the exact reverse of your first trip. But this is more than that; while most time travel takes you to a branching universe, the "Last Time Departed" functionality takes you to the original timeline. So if you used "Last Time Departed" to go to the future, that future will not register anything that you may have changed in the past — it would genuinely be like you never left!

This implies the following sub-guesses:

  • The first film is a bit of Dramatic Irony for Marty; he's completely unaware that he can just hop in the time machine, hit "Last Time Departed", and go back to his former life (and not the Close-Enough Timeline he creates) without having to take any action to get his parents back together. The problem is that nobody told him this was possible; Future-Doc got shot before he had a chance to explain it (and was never planning to send Marty to the past anyway), and Past-Doc hasn't built the time machine yet and doesn't know it contains that function. It is kind of a moot point, because (1) Marty still has to wait for the lightning storm to even be able to power the DeLorean and is at risk of the Delayed Ripple Effect catching up to him while he's still in the past, (2) he actively refuses to use LTD so he can buy himself time to save Future-Doc from getting shot, and (3) he clearly prefers the Close-Enough Timeline in any event.
  • It resolves an inconsistency in what happens when you travel forward in time. The films show different things; in Part I, when Doc sends Einstein one minute forward in time, Einstein never encounters a future version of himself, but when Marty goes forward in time in Part II, we see that there is a Future-Marty. But one would expect, from Einstein's example, that Marty would have gone missing in the future. But LTD can explain it. In Einstein's case, with no LTD, he disappears for the length of his minute-long journey. In Part II, Doc had already travelled to 2015 without Marty and encountered a version of Marty who lived out the next thirty years. Not liking what he saw, he went back to 1985 to collect teenaged Marty and then hit LTD so that he would return to the exact version of 2015 he left — which contains a Future-Marty (and therefore Marty Jr.). It resolves the problem of how you can "extrapolate" what your future self would have done had you not gone forward in time — the only way to do this is to travel with someone else by LTD, and that "someone else" would have already seen it.
  • Old Biff uses this function to return to 2015. He maybe doesn't understand what he's doing, but it's vitally important. Without LTD, the Ripple Effect would erase him from existence once he arrives in 2015, because he gets killed in the Bad Future's 1996 and he shouldn't exist in 2015 anymore. But with LTD, he doesn't suffer any of the consequences of his trip to the past — one of which would be no DeLorean. Without the Delayed Ripple Effect (and its inconsistent application), it explains how the DeLorean doesn't fade out and allows Doc and Marty to leave 2015. (This guess, of course, requires us to disregard the Deleted Scene in which Biff fades out once he arrives back in 2015, suggesting the Ripple Effect did catch up with him. Let's just say that scene was deleted for a reason.)
  • As for why Doc and Marty do encounter the results of Old Biff's time journey, there are several possibilities:
    • The first is a limitation of the LTD protection — it only works on the people who make the journey. Doc and Marty are inattentive and don't notice that LTD is set to 1955 and not 1985, so they use regular time travel and suddenly encounter Old Biff's changes.
    • The second is that LTD only works once per timeline. It's possible to "undo the undo" — if you were to LTD and then go back in your original direction, the changes you made would reassert themselves. Perhaps there's a setting that Old Biff unintentionally tripped to cause that to happen.
    • The third is that Old Biff figured out how to change the Last Time Departed. He was only concerned about Doc and Marty finding out that the DeLorean had been stolen, so he changed LTD to the original 1985 departure date as it was when he stole it. He sees it like rolling back the odometer to obscure a joyride like in Ferris Bueller's Day Off, but he somehow managed to shift LTD from 1955 to 1985 in the same timeline, which is as he left it — with himself in charge. Doc and Marty hit LTD without noticing anything suspicious — and are in for a nasty surprise when they arrive.
  • LTD may also enforce a little San Dimas Time. In the Part II example, Doc and Marty (and Jennifer) leave 1985 in the morningnote , but they return to 1985 in the evening. If they used LTD, they should have arrived in the morning. But it works that LTD takes you not to the exact point you left, but rather a certain amount of time later — the exact amount of time you were gone. And given that they spent most of the day in 2015, they'll have wasted most of the day in 1985. The two trips to 2015 are the only other uses of LTD that we see, and both plausibly run on San Dimas Time — Old Biff got out of 1955 as soon as he could and returned to 2015 soon after he left, and Doc is pretty frantic in 1985 trying to get Marty and Jennifer on the move because if they're too slow, LTD will make him miss his window to intercept Marty Jr. in 2015. If this isn't a requirement of the Timey-Wimey Ball, Doc may have included this feature on purpose to prevent awkward questions of aging.

The entire second and third movies are a result of Doc picking up the Idiot Ball in part II.
Specifically, due to the fact he's too proud to admit that telling people too much about their own future isn't always a bad idea, even after he just ignored it to save his own life.
  • Really, there would be no need to go forward in time to fix one specific problem in the future (which could just as easily be undone as soon as they got back) when it would be easier simply to tell Marty and Jennifer what was going to happen in advance.
  • It also wouldn't be necessary to knock out Jennifer for answering too many questions, leaving her to be picked up by police and trapped in her future home.
  • And then he has an argument with Marty over the almanac, claiming it's a misuse of future knowledge, resulting in him angrily and nonchalantly throwing the book in a trashcan, only to be picked up by Biff. If Marty had kept the almanac, he would certainly be less likely to use it for nefarious purposes than Biff ever would. If the Doc had kept the almanac to destroy it safely and properly later, Biff wouldn't get his hands on it. There would then be no need for the alt-1985 and 1955 segments, and the dangerous attempt to wrest the almanac off young Biff in the middle of a thunderstorm wouldn't have left the Doc trapped in 1885.

Doc and Marty’s friendship started when Doc hired Marty to look after his dog, Einstein.
Also, Marty grew up with a father who was interested in science fiction, which possibly rubbed off on Marty to some extent, and gave Marty and Doc a frame of reference for relating to each other.

Doc and Marty's friendship started because of This is Spın̈al Tap.
There are two strains to this WMG. Either This is Spın̈al Tap and Back to the Future exist in a Shared Universe and Spın̈al Tap is a real band to Marty, or Spın̈al Tap is as fictional to Marty as it is to us. Either way, the documentary (or "documentary") was released in 1984, a year before the events of Back to the Future.

Marty is an impressionable Hard Rock loving teenager who sees the documentary, which includes Nigel Tufnel's demonstration of his famous amplifier that goes up to eleven. Marty is suitably impressed; seeking that extra boost for his own music, he looks up someone in Hill Valley who can build equipment for him. And sure enough, Doc is indeed advertising his services in this field (look at the sign outside his garage in 1985). Marty finds Doc, introduces himself, and asks for an amplifier that can go up to eleven like Spın̈al Tap's. Doc sets Marty straight about the problems with his (and Nigel's) thinking, but does so in an informative and entertaining way so that Marty doesn't feel that stupid. The pair take a shine to each other, and Doc invites Marty to help him build a mega-amplifier anyway — which Marty sneaks in to test in the very first scene of the film.

Clara is fluent in French.
As we know, she is a fan of Jules Verne, but the only English-language translations of his books to exist in her time were terrible—so terrible, in fact, that they caused English-speakers to think, for a century, that only schoolchildren could possibly like them and that they aren’t any good. Therefore, Clara must have read the books in French and was able to appreciate them properly.

Lone Pine Doc is far more cautious than Twin Pines Doc... and for good reason.
Consider the fact that the Doc in Part II is livid at the fact that Marty wants to buy a book on sports statistics from the future and place a few bets, yet in the Twin Pines timeline in the first movie, he wants to find out who won the net 25 World Series (possibly with the intention of betting on them, but it isn't clear). Also, when you consider how nuts he is in even setting up the time travel experiment the way he did- utilising an unlicensed nuclear reactor (almost certainly illegal) powered by stolen plutonium (definitely illiegal) he obtained by ripping off very dangerous terrorists without thinking they might come and kill him... all For Science!

But in the Lone Pine timeline, Doc has had experiences his Twin Pines timeline counterpart has not. He's seen the potential consequences of messing up the timeline (Marty nearly erasing himself from existence) and also the terrorists' threat to his own life, which he's prepared for. This Doc is much less likely to take chances of any sort than the original Doc.

Of course, by the end of Part III, and after the obvious passage of many years, his regrets about ever having made the time machine (as of Part II and most of Part III) are allayed. After all, everything worked out fine and he has a happy life with a wife and kids... so he thought, "What the hell!" once more, and made a locomotive time machine...

Had there been a fourth movie, it'd show Needles watching a basketball game.
During the video call between Marty and Needles, "avid basketball fan" was listed as one of Needles' hobbies. Needles watching a game would be a nod to that.

The timeline shifts perhaps once every millisecond.
The Universe is gargantuan. Someone somewhere in the universe is always playing with time, or reality-shifting magic (for example "Spells R Us" and its subuniverse "Bikini Beach"). People may notice the reality shifting as it occurs, but then their memories have been reality-shifted so that they only remember the current reality. If reality shifts once every millisecond, they perhaps remember and see the reality as it was several minutes earlier.