Question: Doc has always been firm about not wanting to create some sort of paradox. Was he not at all worried that eventually someone would go into his barn looking for him and find his giant refrigerator and his model railway with the car that said "TIME MACHINE" on it? I know he stayed behind after he rescued Clara so could have removed all that, but the original plan was he was going to hop into the DeLorean with Marty. We know he definitely left the model railway there as Clara picked the car up which prompted her to go after him.
Answer: Well everyone in that town knows Doc's a pretty smart guy. Chances are he was doing some experimenting with time machines or something. The average person I'm sure would never figure it out anyways or think it was a crazy irrelevant project. Clara only figured it out because Doc told her about the time machine and time travel and thought Doc was lying to break up with her. The story sounded crazy until she saw the model, then saw the machine and realised he was telling her the truth. But the average person in that period knows nothing about the time machine, cars, or rime travel and even if they by some chance figured out Doc was from the future nobody would believe it nor could they prove it.
Question: Doc is quite a resourceful and clever guy. Why didn't he set to work on repairing the flying circuits which would have enabled them to use Mr Fusion to reach 88mph, instead of the engine?
Answer: Mr fusion only powers the flux capacitor. The engine is needed to get the car up to 88mph whether flying or not and the only way to get the car any power is by the use of petrol, which didn't exist in 1885.
At the beginning of the movie, when 1955 Doc reads the letter that 1985 Doc sent to Marty, he reads that the lightning bolt activated the time circuits and at the same time destroyed the flying circuits. Because of this, the Delorean will never fly again.
These answers are correct. Plus, to the original question: as clever as Doc is, keep in mind he got the flying conversion done in 2015. Definitely no way he would have been able to repair something so futuristic with 1885 tools at his disposal. He couldn't even get gas.
Yet just a few years later he had built from scratch a flying time-traveling locomotive, all with 1885 tools and parts.
There's no indication he built the flying train in 1885. It's suggested he had been time traveling with his wife and kids and says he's already been to the future. Whether this is in the DeLorean or the train it's not clear, but the dialogue suggests he's been to the future in his train with the family and could have modified his train to fly with future technology.
Question: When towing the car across the desert, why did Marty keep checking the speedometer? Did he really expect a horse to gallop at 88MPH?
Answer: At that point in the film, Doc and Marty were looking for any possible means to move the DeLorean regardless of how fast it could actually go; while using horses may have been an unlikely option, Doc and Marty were just grasping at straws at that point and were willing to try anything.
But then Doc says that even the fastest horse in the world could only run at 35 mph so why even try it.
Answer: They were using the horses to get the DeLorean from the cave to the town. Why not test the speedo at the same time?
Question: How did the new gauge in the car read the boiler temperature? It wasn't connected to the train at all.
Answer: It was based on the speed the train, and therefore the car, was travelling.
Question: Why did Clara go mental at Doc for saying he was from the future? He'd dropped a few hints! He'd told her he has an interest in science, he had a huge refrigerator in his building, he had another big thing covered up under a sheet, he said he read Jules Verne when he was a boy despite it only been recently published. Was she not even a little bit curious? Doc could have easily stopped her during her rant saying he can prove it but didn't.
Answer: Because she thought he didn't like her and was making a bizarre excuse to avoid her. Come on. 'I'm a man from the future, so we can't be together ' sounds like a pretty flimsy excuse.
Question: Back in 1885 why doesn't Doc change the letter he sent to Marty, asking him to bring a can of gas?
Answer: When Marty received the letter from Doc in 1955, as seen in the second movie, Doc wrote down that he didn't want Marty to go to 1885 to rescue him because he was happy living in the past. Instead, he wanted Marty to take the Delorean straight back to 1985 and then destroy it so it could never be used for personal gain again.
But once Marty appears in the past Doc could easily change the letter, changing things such that Marty would bring gas with him.
Answer: This would create a different timeline, not the timeline they are in.
Answer: That would not be possible as in 1885, Doc sent the letter on September 1st, and 1955 Doc sent Marty to 1885 on September 2nd so it was a day later and on the 1st, Doc was not expecting Marty to turn up. However, one CAN ask why Marty and Doc didn't go to the local Western Union office and change it (or write a new one) there since it was in their possession per the gentleman in part 2.
Changing the letter while Marty is in 1885 with Doc would accomplish nothing, because it doesn't it instantly travel to the future. Marty at the end of Part II, for his part, may receive the letter almost immediately, but the letter itself had to wait 70 years to be delivered to him.
I mean, there's no solid rules to time traveling, but just for argument's sake it seems like the letter idea could work... in the franchise, when something is set in motion, the effects usually take place immediately. Take for instance when George and Lorraine kissed at the dance in Part 1. The picture of Marty and his siblings went right back to normal, even though the kids had not been born yet. Doc and Marty changing the Western Union letter "could" have had an immediate effect and a gas can could have materialized in the Delorean, much like we've seen newspaper headlines change before our very eyes, disappearing gravestones, etc.
In your examples, the changes occur to future events. The items that changes, like the picture and newspaper, are from the future themselves. They can't change the past by changing events in the future (like they do in Bill and Ted's). This is why Doc and Marty couldn't go back to 2015 to stop old Biff from taking the DeLorean.
Question: Marty tells Doc that they are out of fuel as the fuel line ripped on the car. Wouldn't it have made more sense for them to uncover the DeLorean that Doc buried, put a piece of paper on the seat with a note saying something like... "Oh Marty, I forgot to mention in my letter that the car needs some extra fuel. Keep a can of gas with you in the car at all times" - Hey presto, Marty would have arrived with extra fuel! Now obviously I hear you shouting "continuity" and "It would be an alternate timeline like in part 2" - But that didn't stop Biff taking the car back to the 2015 Doc and Marty were in, despite Doc later saying if they travelled into the future it would be the rich Biff reality.
Answer: Although Biff in part 2 is its own set of problems, the answer to your question actually doesn't have anything to do with continuity or alternate timelines. They can't risk disturbing the Delorean that Doc burried in any way. It has to remain exactly as it is, otherwise at best Marty is stuck in 1955, or at worst they create a paradox that destroys the universe. It is best to ignore the buried Delorean, any attempts to get to it could lead to it being damaged, or even worse could lead to it being discovered in the 70 years it has to remain in that mine.
Answer: It would have been easier for Marry and Doc to go down to Western Union and ask for a second letter to be delivered with the first. The letter would say "Ignore the comment in the first letter about not going back to 1885, please come to 1885 and bring some extra fuel with you"
Question: Doc Brown shows up at the end of part three with his wife Clara, his two boys, and a time-traveling, hovercraft-converted train. How did he build it? There was nothing in 1885 that could even begin to help him build another time-machine! And don't tell me that he used Marty's 'hoverboard' as parts, because that doesn't wash.
Chosen answer: Time machines don't actually exist, so who are we to say whether or not the parts to build another time machine are available? Doc Brown is an inventor. Doc had the knowledge of how to build a time machine having built the original machine into a DeLorean, Doc also appears to have had a few years to come up with a way of building a time machine into a train, given that he now has children who appear to be around 5 years old. Plus, remember that the fridge in Doc's shop was much bigger than a modern fridge, and a steam train is way bigger than a DeLorean.
Answer: Doc's consistent problem was finding high-energy power sources for his inventions. But, actually, materials and technology did exist in the late 19th Century to construct extremely high-energy components. If Doc Brown had contacted electrical geniuses of the day (such as Nikola Tesla, who was already working in high-energy physics, radio and and X-ray technology in the 1890s), he could have certainly acquired the materials to reconstruct the Flux Capacitor and back-engineer hover pads for his time-travelling locomotive. As we saw earlier in the film, he was quite capable of back-engineering 1980s electronics using 1950s components (when he repaired the DeLorean).
Question: In 1955 when Doc and Marty are in the outdoor cinema and Marty is accelerating to 88mph to jump back in time to 1885, doc shouts something to him in celebration as Marty Drives past him, he also fires his gun in the air... Do you know what he shouts? The subtitles just say "shouts something in Spanish" but id love to know what he said and what it means?
Answer: The subtitles are wrong! I always heard him shout "to the ends of the Earth " A reference to Jules Verne (keeping that theme running all through the third movie) and to Marty's adventures. Not only is this what I've heard every time I've watched this film, but it makes much more sense.
This is incorrect. He does in fact yell "Vaya con dios." The scene is available on Youtube and he can be seen and heard saying it at the 2:47 mark. https://www.youtube.com/watch?v=zV9udBGZio4.
Question: For Doc to be so worried about corrupting the timeline in this movie (especially when it comes to falling in love with Clara) he surely doesn't seem to think twice about destroying the locomotive that will no doubt have a huge effect on the timeline. I doubt there were many trains on that railroad, with that mode of transportation now gone, Hill Valley itself could be wiped out.
Answer: Doc must have reasoned that the loss of the locomotive would have a minor impact on Hill Valley, if at all. The railroad company would likely have replaced the destroyed locomotive. Obviously Doc was correct as there seems to have been no impact on Hill Valley's economy whatsoever and the train lines continue to run into the 1980's.
Answer: Corrupting time was a worry for Doc, however, he also recognized that it was at least partially unavoidable. Otherwise, Doc would never even be able to go buy food, because how would he know that the meal he ordered wasn't one that someone else was meant to choke on? Occupational hazard of time travel.
Chosen answer: In the timeline that the original Marty and Doc came from, Hill Valley exists so that town obviously survived that incident. An accident already occurred on that day in their history. They just didn't know it was them that caused it.
That is not how time travel works in these movies. In fact, the entire series revolves around the timeline being changed whenever they travel into the past. There are no stable time loops. The train was not destroyed in the original time line.
It's tough to say whether or not the train wasn't destroyed in the original timeline. Maybe by some lucky chance the train would suffer an accident similar to that anyways maybe just a bit earlier. There's really no indication either way. It's also possible they build another train or had others in service. I doubt they didn't have some backup plan in case the train was out of commission for a long period of time or destroyed.
Question: Doc is a scientist right? The DeLorean had a ruptured fuel line and needed gas which, as Doc pointed out, was unavailable at the time. Surely he knew how to distill booze to make ethanol? (There was plenty of whiskey around at the time). I mean, they've used it to power cars in Mexico for ages. Why didn't Doc suggest this?
Answer: They did try it. Doc ran the engine with the strongest thing the bartender could find them and it blew out the engine. It takes all the power a heavy car like a DeLorean has to get up to 88 MPH. It wouldn't be able to get that much power running on ethanol, in addition to the damage caused to the engine.
Question: When the 1985 Doc is suddenly transported back to 1885 at the end of BTTF 2 and Marty discovers that he has been murdered, because there is a Doc in 1955 that has already been born after the 1985 Doc has died in the West, why did he go to the trouble of going all the way back to 1885 when Doc was still alive? Is there any actual legitimate time travel reason for this, or did he just do it out of instinct to help his close friend?
Answer: Technically when Doc got transported to 1885, he should not have existed in 1955 because he died. This is the problem I'm having with part 3. The movie should not have happened this way. It should have been where doc did not exist nor the time machine. Part 3 should've never happened.
That's not how most time travel (if any) stories work. Just because someone dies in the past doesn't prevent them from being born since they were already born and alive before going to the past. Think of it this way, if instead of 1885 he travelled to 2085 and died, would that prevent him from being born? The only reason Marty was in danger of disappearing and not existing (i.e. being born) was because his parents were in danger of never getting together.
It was the 1985 Doc that went back to 1885 so he would still be alive in 1955.
The Doc that got sent to 1885 was the Doc from 1985 so therefore it wouldn't have affected 1955 Doc at all.
The one in 1955 hasn't done anything 1985 Doc did.
Question: Just wanting to know about the animal running in front of the Native Americans when Marty travels back to 1885. Looks like a dog, but was it meant to be there, or was it an animal that was disturbed as they did the scene and it bolted for its life?
Answer: It is a rabbit that probably got disturbed by the filming.
Answer: Someone would go into his barn and do what? See a sign that says time machine and believe it and then use it? Seems highly unlikely.
lionhead