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In Harry Potter, it seems like Time Turners are mostly used to correct minor things or do things that wouldn't have any major effect. Also, in Prisoner of Azkaban, it seems like Time-Turners/time travel is strictly "fated" or already predestined by history (time travel doesn't really change anything--rather, it ALLOWS what was already meant to occur to happen). This is shown when Harry and Hermione rescue Buckbeak and Sirius, and Harry saves his past self.

In time travel theory, this is called the Novikov Self-Consistency Principle, which states that "Nothing can be changed because anything a traveler does merely produces the circumstances they had noted before travelling".

Now, here's my question. In the book, it also states that wizards have accidentally killed their past or future selves while time travelling. But how is this possible under the Novikov Self-Consistency Principle?

Lastly, if someone were to die, does that mean that someone else could use the Time Turner to quickly stop that person from dying in the past?

EDIT: It's different than the question linked above because I never asked if going forward in time is possible in Harry Potter. I asked how is murdering past or future selves possible under the theory noted above, and how if it would be possible to go back in time to prevent someone from dying.

closed as too broad by Voldemort's Wrath, TheLethalCarrot, Skooba, DavidW, Edlothiad Aug 16 at 13:38

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    What "minor" or "ineffective" corrections in time are you referring to specifically? – Slytherincess Oct 14 '14 at 3:27
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    ...I never edited anything..? My question has always remained the same. Also the question that you linked up above doesn't even pertain to my question. I never asked about going forward in time. – Zack Oct 14 '14 at 19:19
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    @Slytherincess: I don't understand how this question is a duplicate of a question asking if time-turners are one directional. – Ellesedil Oct 14 '14 at 19:58
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    Where is forward movement in time mentioned anywhere in this question? – Ellesedil Oct 14 '14 at 20:02
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    Please limit this to a single question so that it is answerable... As it stands, your post contains multiple questions... – Voldemort's Wrath Aug 16 at 13:14
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I'm not sure you're basing your assertions on the correct theory of time travel. J.K. Rowling says:

In spite of the many Muggle fantasies around the subject, time travel is possible in only a limited sense even in the magical world. While the subject is shrouded in great secrecy - investigations are ongoing in the Department of Mysteries – it appears that magic can take you only so far.

According to Professor Saul Croaker, who has spent his entire career in the Department of Mysteries studying time-magic:

“As our investigations currently stand, the longest period that may be relived without the possibility of serious harm to the traveller or to time itself is around five hours. We have been able to encase single Hour-Reversal Charms, which are unstable and benefit from containment, in small, enchanted hour-glasses that may be worn around a witch or wizard’s neck and revolved according to the number of hours the user wishes to relive. All attempts to travel back further than a few hours have resulted in catastrophic harm to the witch or wizard involved. It was not realised for many years why time travellers over great distances never survived their journeys. All such experiments have been abandoned since 1899, when Eloise Mintumble became trapped, for a period of five days, in the year 1402. Now we understand that her body had aged five centuries in its return to the present and, irreparably damaged, she died in St Mungo’s Hospital for Magical Maladies and Injuries shortly after we managed to retrieve her. What is more, her five days in the distant past caused great disturbance to the life paths of all those she met, changing the course of their lives so dramatically that no fewer than twenty-five of their descendants vanished in the present, having been “un-born”.

Finally, there were alarming signs, during the days following Madam Mintumble’s recovery, that time itself had been disturbed by such a serious breach of its laws. Tuesday following her reappearance lasted two and a half full days, whereas Thursday shot by in the space of four hours. The Ministry of Magic had a great deal of trouble in covering this up and since that time, the most stringent laws and penalties have been placed around those studying time travel.

”Even the use of the very limited amount of Time-Turners at the Ministry’s disposal is hedged around with hundreds of laws. While not as potentially dangerous as skipping five centuries, the re-use of a single hour can still have dramatic consequences and the Ministry of Magic seeks the strictest guarantees if it permits the use of these rare and powerful objects. It would surprise most of the magical community to know that Time-Turners are generally only used to solve the most trivial problems of time-management and never for greater or more important purposes, because, as Saul Croaker tells us, "Just as the human mind cannot comprehend time, so it cannot comprehend the damage that will ensue if we presume to tamper with its laws.”

The Ministry’s entire stock of Time-Turners was destroyed during a fight in the Department of Mysteries about three years after Hermione Granger was granted permission to use one at Hogwarts

Pottermore*

No, I don't think someone could go back in time and keep someone from dying, unfortunately. In my second bolded paragraph, I note that Time-Turners are typical used for trivial matters of time management (as you noted originally :) )

Also, if you're interested in time travel in Potterverse, there's a very good essay on the subject at The Sugar Quill: Time Travel in Harry Potter.

  • Yes, but what the essay states applies to the Novikov Self-Consistency theory, and everything in PoA does as well. So that is why I'm wondering how it would be possible for a witch/wizard to kill his past self during time travel, if you are therefore not alive to go back in time to do the killing. The essay touched on this but said that the paradox is only in the mind, which I don't understand. – Zack Oct 14 '14 at 4:36
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    @Zack: How do we know that Buckbeak survived "before" H&H went back to save him? All we know is what they did, which was an axe striking something and Hagrid crying. – George T Oct 14 '14 at 7:44
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    Because Harry saw himself casting the Patronus Charm, meaning that the events of the time turner were already being done. – Zack Oct 14 '14 at 19:16
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    Your quote does not at all support your claim that people could not go back in time and save someone from dying. Consistent or not, the quote says that going back in time might cause people to become 'unborn'. For the vanishing to have been noticed, others must have seen those people and then suddenly noticed that they were gone. How that could possibly work is of course unanswered by the quote, and most interpretations of the quote are actually inconsistent. – user21820 Nov 27 '16 at 11:16
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According to the way time travel is portrayed in Prisoner of Azkaban, it should indeed be impossible to kill your past self. If you kill your past self while you were back in time, you wouldn’t have been alive to go back in time in the first place.

However, it would seem to be possible, in theory, to kill your future self. If you go back in time and get killed, presumably all that happens is that you never return to the present. An observer might see you disappear when you turn the time-turner and then you’d simply never reappear. There doesn’t seem to be a reason why your past self would be the only person in the past that is unable to kill you. Your past self’s Avada Kedavra should be just as effective as anyone else’s.

On the other hand, if you kill your future self it would be quite foolish to then go back in time. Doing so would only lead to your own death. In that sense it may be somewhat of a paradox, because if you already killed your future self, you can’t possibly not go back in time, because without going back in time you couldn’t have been killed by your past self. Or phrased in the reverse, since you wouldn’t go back in time if it meant you’d be killed, your future self would never have been present in the past for your past self to kill.

There are, however, a few possible exceptions:

  • You want to die.
  • You don’t realize that the person you killed is your future self.
  • Someone forces you to go back in time.
  • Not knowing how time travel works, you go back in time precisely to prevent yourself from being killed, but that doesn’t work.

In any event, it would seem that Hermione’s statement is at best imprecise, and at worst entirely untrue. We could suggest that McGonagall deliberately gave her misinformation about people killing themselves, in order to scare Hermione away from using the time-turner for anything but the intended use of taking multiple classes at the same time. Indeed, it seems fairly clear that Hermione is not aware of how time travel actually works, given that throughout the adventure she seems to assume that it is in fact possible to change the past (e.g. Buckbeak actually died and they will now prevent that from happening).

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