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In Back to the future II, Marty burns the almanac in the bucket and Doc's DeLorean was struck by lightning, causing doc to travel to 1885 accidentally. Then Marty receives a letter from Doc which was written in 1885, saying that the time machine is at so and so place and do not come to 1885. Then Marty runs to Doc present in 1955, who has just sent 'other' Marty to 1985. The Marty says that, he's back from the future.

My question here is that, Doc goes to 1885 and he dies at the hands of Biff's Great grandfather. Then according to the timeline ripples, Doc will never be present in 1955. Thus all the events involving Doc after his death should have been altered. Just the time machine would be there at that place.

How did Marty meet Doc then (in 1955 for the second time)? It would be like a time loop that time machine was not created later (1985), it has been present before (1885) only and it makes the plot wrong.

Am I missing something here?

  • Because Marty went back and saved him...temporal mechanics make my head ache. – Paulie_D Aug 25 '16 at 8:41
  • @Paulie_D Marty went to 1885 after the event I have mentioned. Then he saved Doc. Doc must be there in 1955 to send Marty to save himself in 1885. – kvchivukula Aug 25 '16 at 9:12
  • Um, wasn't the Doc that died just the one who travelled back? The Doc from 1885 is not the same Doc who later met Marty in 1955, since that Doc wasn't even born yet. – Napoleon Wilson Aug 25 '16 at 9:32
  • @kvchivukula So what you mean is that Marty couldn't meet Doc in 1985? That makes more sense indeed, but didn't really seem to come out of your question. – Napoleon Wilson Aug 25 '16 at 9:43
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    Ok, there's an explanation. Don't know whether it is correct or not. Doc is born in some 1920s, made time machine in 1985, went to 1955, a brief interaction with his other self (let it be Doc-2). Then goes to 1885 by lightning. Dies there in 1885 September. So, he died before he was born. So, it doesn't change events in future like birth of Doc, meeting Marty in 1955,making of time machine etc. Is there any wrong? – kvchivukula Aug 25 '16 at 10:08
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The Doc Brown in 1955 is younger than the Doc Brown in 1885, by 30 years. The Doc Brown in 1955 will still live for another 30 years before traveling back to 1885 and being shot by Buford.

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    This is the correct answer. If the Doc in 1955 was a future version of the killed Doc, why would he be surprised to see Marty? He would have written the letter and foresaw the events taking place. – Kalamane Aug 25 '16 at 21:59
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If someone went and killed an incarnation of Doc, present at that point in the timestream, it would have a ripple effect on the future.

Killing a fully grown adult Doc, not at his fully-grown point in time, but rather killing a Doc who was never in a time period, who is only visiting that time, would not have implications on any Doc, because the death of someone who traveled back to another time period as an outsider would not be altering events that happened before in the original Doc's life.

There was nothing in Doc's life, prior to 1955 that is effected by a post-1955 version of him getting killed in 1885. That 1885 event happens before 1955, technically, but it's not a pre-1955 Doc who is getting killed.

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Then according to the timeline ripples, Doc will never be present in 1955.

By that logic, no one would ever be able to travel into the past unless they would be able to naturally live out their life to come back to the point in time they travelled from. If you had 50 years of natural life left, you then wouldn't be able to travel 51 years into the past.

You're misunderstanding how time travel in BTTF works. Doc can invent the time machine, travel to the past, and die, without destroying the causal link.

You seem to think that when you travel to the past, you become "younger", but that is not the case. This is easily shown when future Biff (the old guy) travels back to 1985. After traveling, he is still an old man (compare him to 1985 Biff, who he has a conversation with).

The only paradox would be if Doc Brown travels into the past, e.g. to 1954, and burns down his laboratory (or kills the 1954 version of himself) so that it's impossible for Doc (in 1955) to invent the time machine. These are all variations on the grandfather paradox, which specifically revolves around changing the past in a way that the time travel event (in the relative future) becomes impossible (either by prematurely killing the time traveler or making his time travel impossible to have happened).

Similarly, if Doc had decided to invent and publicize the time machine in 1885, it would have become commonplace well before 1955 and the "original" Doc Brown in 1955 would not have needed to invent a time machine, thus creating a potential (though resolvable) paradox.

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You most definitely missed something.

The trilogy goes in this order and they all take place in the year 1985:

  • Back to the Future (1985)

  • Back to the Future Part II (1989)

  • Back to the Future Part III (1990)

It is the older 65-year-old doctor who dies in 1885; not the younger 35-year-old man. An old man dying in the past has no effect on himself being born later.

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Parallel Worlds and Time Travel go hand in hand. Like the saying goes you can't change the past all. So beginning in the first movie, BTTF1, Marty lives an unhappy life with unhappy parents, has a somewhat happy attitude because he spends time with Doc Brown being an assistant of course (if you read the comics). Now, When Doc finished his time machine, he input the date Nov. 5,1955 I'm assuming around 5 or 6am in the morning, and when Marty saw Doc get shot by the Libyans, Marty screamed "No, bastards" and gained the attention of the terrorists and the terrorists knew that they couldn't live no witnesses behind. so they were aiming to kill Marty as well, and they would have if that gun didn't get jammed up. And therefore Marty saw an opportunity to escape and took advantage of the opportunity, but when he was escaping from the Libyans he didn't notice that he had turn the time circuits on. and therefore when he saw the bazooka, aiming at him, he said: Let's see if you can do 90 and when the delorean hit 88 miles per hour he time traveled from 1985 to 11/5/1955. And somehow before Doc did his bruise which is the reason why Marty had to mess with his parents meeting otherwise doc would have never invented time travel. and then he got his parents back together before he faded into nothingness.

Now I'm skipping the argument about the future version of their-selves but short version is that time predicts that the time traveler makes it back to their original place in the timeline. Or time assumes that they do. Unlike for example Doc's case.

The Doc from 1985, was in the Delorean when it got struck by lightning and got sent from 1955 to 1885, and the doc from 1985 got shot in 1885 and therefore THE DOC from 1955 would still exist no matter what. And therefore Marty knew he couldn't mess with the clocktower problem until he double went back to 1985 originally. And this is why the Marty also from the year 1985 (but later in the day than the previous Marty who was just sent to the future earlier.) And therefore Marty was able to meet the Doc from 1955 again for the second time.

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