Time Travel and Paradoxes in Harry Potter:

[Sensei Kiisu]

I deem this the most appropriate forum for this topic, as it deals with scientific speculation into Time Travel and Paradoxes.

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I have recently become confused and baffled trying to work out events that we read and see in the novels and films of Harry Potter, specifically the third book/film in the series, the Prisoner of Azkaban. In this, we come to learn that Harry saves himself and his God father, Sirius Black, from a terrible fate, the Dementor's Kiss, and also the death of the hippogriff, Buckbeak. In more detail, Harry and Hermione by use of a Time Turner, travel back approximately three hours (we assume), in order to free Buckbeak, save past-Harry and Sirius down by the lake, and then free Sirius from his capture. (Of course, many people choose to use the school-boy excuse of ‘they are magic, thus anything is possible’, however - since they need to use a device to travel back in time, as would we, let's say for this argument that the laws of time and physics are the same as what we have.) Now, I see the first paradox here:

How is it possible for Harry to travel back in time to save himself?

At first glance it seems pretty easy and believable that Harry and Hermione go back in time to change the events in their favour, however - when thinking about it for around a minute, obvious flaws start to appear.

If we assume that the single thread of time (un-tampered with by external influences of time travel) is allowed to play out, then we would see that down by the lakeside, Harry and Sirius, outnumbered by Dementors, have their souls sucked out of them, and become shells of their former selves. Taken back to the hospital wing eventually, it would now be impossible for the virtually lifeless Harry Potter to go back in time to save himself and others, since he physically isn't able too, THUS - the events that we read and see of Harry seeing himself conjure a Patronus can simply not have happened... that is - without the time-line already being interfered with.

An explanation I came up with is this; what if someone else had already interfered with the constant thread of time, thus making Harry's already tampered with. Now who has the knowledge and motive to do this? As we read and see, Dumbledore seems to know more than he lets on, he even tells Harry and Hermione to go back in time and change the events. Now, if Dumbledore, and not time-traveler Harry, had been the one to see the un-tampered with events unfold, then he would see Harry and Sirius being brought into the hospital wing, soul-less. He knows that without Harry, Voldemort can not be defeated, and so he simply must go back in time and alter the events.

Let's say down by the lake-side time-travelling Dumbledore saves them both, this would then allow for the possibility of Harry and Hermione able to go back in time themselves to save Sirius and Buckbeak. (Of course Harry must save himself whilst he travels back in time also, since him travelling back in time would mean that the line of Dumbledore saving Harry is erased, and therefore if he does not save himself, then there is no-one to save him, which would thus cause his own demise.) Now, here is a plausible theory unto how Harry came to save himself at the lake, (technically it was really Dumbledore, however to him that never happened since that time-line has vanished) - it allows for Harry to be physically able to have been in two places at once.

However, after finally feeling pleased that I had come up with an explanation, it hit me that this also is not possible. Why? Yet another paradox. Paradox 2.

You can't go back in time to change things that you already know happen, because as you already know: they happened.

This may sound confusing however the explanation is simple. Basically, if you saw something take place at 7 p.m. and then at 11 p.m. you go travel back a few hours to change it, your past self does not see the event that you have changed to take place, so therefore when 11 p.m. finally comes, your past self does not know to go back in time to change said event, because to them it has no occurred - therefore, you could not have possibly have time-travelled to change something you did not know to change.

In Dumbledore's case, he knows exactly what events have happened, in this case knowing that Harry and Sirius are going to receive the Dementor's kiss. Thus he travels back in time to prevent this from happening. Now that the Future Dumbledore has changed what his normal self knows to have happened, when it would come to the point in the time-line where Dumbledore would travel back in time to save Harry and Sirius, how would he know to travel back in time to do so, and therefore who would save Harry and Sirius? I hope that makes sense...

So ultimately, at the present moment my opinion is that the events that we see in the books and films are illogical since there is no way that Harry could go back in time to save himself, unless anyone has different ideas unto how time-travel works and how it could be possible for this to happen.

-- While writing this it did occur to me a way in which Dumbledore could in fact have been able to 'know' to travel back in time to change the events. Let's say he has travelled, and saved Harry and Sirius. He then places his memories of him doing so into his pensive, (which from the books we know stores past events, so who is to say it cannot store future/alternate ones). Now is it feasible that the normal Dumbledore accessed these memories some-how and realised that he must go back in time to save Harry and Sirius? Of course it'd have to be by pure chance and would be very risky relying on this to happen... making this even more unlikely.

However again, I find myself finding flaws in my own theories yet again – if he did view these memories, then the time-line that he is living is NOT the same one that is originally played out (since there are millions of millions of possible time-lines) and therefore he would be travelling back into what is technically an unknown time-line… I believe that this is the reason that Dumbledore says that there is no spell nor way to bring back the dead, because even if you tried to change something that you know happens, you end up making it an alternate point of time, which would not affect the one you are in, and thus be useless to you.

If there is one thing that has come with me pondering over this however, is that even though I’m still as confused as I was before writing this over what we read in the books and see in the films, I have sorted out in my own mind, why the dead can not be brought back to life via time-travel.

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Thank you for reading.

[Gaidin]

It's not an engineered device, it's an artifact. The laws of physics are moot.

[Sensei Kiisu]

I'm sorry but trying to de-bunk my whole theories there with a blanket statement like that doesn't really help anyone XD...

I've seen this similar scenario in many films not just the HP series, - i.e. people going back in time to save themselves or another person... - the whole idea of this is to judge if there is a feasible way in which someone COULD possibly go back in time to do the above.

[Gaidin]

I'm sorry but trying to de-bunk my whole theories there with a blanket statement like that doesn't really help anyone XD...

I've seen this similar scenario in many films not just the HP series, - i.e. people going back in time to save themselves or another person... - the whole idea of this is to judge if there is a feasible way in which someone COULD possibly go back in time to do the above.

Asking about the physics with a magic item doesn't pan out. The point of magic is it defies the laws of physics, except maybe the Conservation of Energy laws. And that depends on what story you read. Harry Potter couldn't care less.

[Manco]

I don't really see the confusion.
Potter gets saved and later realizes it was he himself who saved him. There's no need for alternate timelines, since it all takes place in the same one, he just jumps back in it.
The future or past aren't changed at all, everything Potter does after jumping back takes place as originally described when he got saved.

You're asuming this :___________________ original timeline plays out
..........................................\_____________ Timeline where Potter saves himself
(ignore the dots, I forgot the proper code to leave spaces)

What's described in the book is: ____X1__________X2________
Potter jumps from X2 to X1 and avoids his earlier version till that version has once again jumped to X1

I'm sorry but trying to de-bunk my whole theories there with a blanket statement like that doesn't really help anyone XD...

I've seen this similar scenario in many films not just the HP series, - i.e. people going back in time to save themselves or another person... - the whole idea of this is to judge if there is a feasible way in which someone COULD possibly go back in time to do the above.

The difference with most other movies and stories is that in those stories events are altered. Nothing changes in the Potter version

[Juvenal]

Shame on you Gaidin, there are always rules, even for magic. Otherwise the story would be completely arbitrary and therefore an unsatisfying experience for both author and reader.

I think that Sensei Kiisu's difficulty is in the assumption that there was an original non-looped time-line, and that there is some kind of meta-time in which time-line changes can play themselves out.

The looping time-line where Harry saves himself is inherently self-supporting. There does not need to have been another time-line "earlier" in meta-time where Harry didn't save himself. Indeed such a thing is impossible since you can't get from there to the events that actually do happen in the story.

Since nothing more is said about time travel in Harry Potter (as far as I know), you cannot tell whether the Past is fixed or changeable. If it is fixed, then Harry saves himself because he has been saved, and no further justification is needed.

But if the Past is changeable, then you can have paradoxes! This is much more interesting because Harry now has the option of failing to save himself. So, how to resolve the paradox?

If you subscribe to the idea of parallel universes, then you can side-step the paradox. By failing to save himself Harry simply branches into a parallel time-line where he had died. So upon his return to the present in the new timeline, everyone would be somewhat surprised to see him still breathing, especially since his corpse would be there already!

But without parallel universes, we are faced with the paradox in its full glory. This means that if Harry deviates from what is required to maintain his past, then his past will change! Many authors have tackled time-travel with paradoxes, but I have yet to come across a treatment I am completely happy with, probably because they make for disjointed stories. However, consider this. Harry is about to cast his Petronus to save his earlier self from death. If he fails and his earlier self dies, then his later self presumably must cease to exist immediately since his past no longer exists!

[Tacitursa]

Pretty much the same problem i have with terminator movies. How is john connor born first time around if in order to be born he has to get to the future and save his dad , then send him back in time to protect his mum.

The future must happen before the past in both harry potter/terminator it doesnt make sense.

[Gaidin]

Shame on you Gaidin, there are always rules, even for magic. Otherwise the story would be completely arbitrary and therefore an unsatisfying experience for both author and reader.

I think that Sensei Kiisu's difficulty is in the assumption that there was an original non-looped time-line, and that there is some kind of meta-time in which time-line changes can play themselves out.

The looping time-line where Harry saves himself is inherently self-supporting. There does not need to have been another time-line "earlier" in meta-time where Harry didn't save himself. Indeed such a thing is impossible since you can't get from there to the events that actually do happen in the story.

Since nothing more is said about time travel in Harry Potter (as far as I know), you cannot tell whether the Past is fixed or changeable. If it is fixed, then Harry saves himself because he has been saved, and no further justification is needed.

But if the Past is changeable, then you can have paradoxes! This is much more interesting because Harry now has the option of failing to save himself. So, how to resolve the paradox?

If you subscribe to the idea of parallel universes, then you can side-step the paradox. By failing to save himself Harry simply branches into a parallel time-line where he had died. So upon his return to the present in the new timeline, everyone would be somewhat surprised to see him still breathing, especially since his corpse would be there already!

But without parallel universes, we are faced with the paradox in its full glory. This means that if Harry deviates from what is required to maintain his past, then his past will change! Many authors have tackled time-travel with paradoxes, but I have yet to come across a treatment I am completely happy with, probably because they make for disjointed stories. However, consider this. Harry is about to cast his Petronus to save his earlier self from death. If he fails and his earlier self dies, then his later self presumably must cease to exist immediately since his past no longer exists!

Problem being that Harry Potter sucks at defining those rules and they certainly don't square with physics, meaning that we really can't answer this question. At all.

[Tacitursa]

Harry cannot live unless he goes back in time to save himself, and he cannot go back in time to save himself unless he is alive. The fact that he achieves both these things justifes the fact that he is alive because he went back in time to save himself. You can travel around that loop for ever, and you will not come to any point at which he saves himself and yet is not alive, nor vice versa. The one depends on the other.

I understand how it works but it's still impossible.

[Elfdude]

Time isn't a linear progression. There is no paradox, just an issue with the popular conception of time itself.

[Copperknickers II]

Exactly Elfdude. What Harry is doing when he uses the time turner is creating a loop in the thread of time.

Harry cannot live unless he goes back in time to save himself, and he cannot go back in time to save himself unless he is alive. The fact that he achieves both these things justifes the fact that he is alive because he went back in time to save himself. You can travel around that loop for ever, and you will not come to any point at which he saves himself and yet is not alive, nor vice versa. The one depends on the other.

[conon394]

Problem being that Harry Potter sucks at defining those rules and they certainly don't square with physics, meaning that we really can't answer this question. At all.

However when authors start tying to jam all that explanation in to story it tends to bog down and become boring and likely open up a whole host of fine points that contradict one another if you forget some exact rule you made before...(*) In this case however the lack of definitions makes sense since the story is after all told from Harry's view point and is more or less a slacker who is not really interested in the how and why of magical 'physics' for all his talent unless pushed to it by need (in this consider the obvious and complete disinterest He and Ron show the odd behavior of Hermione over the term - had he given the matter half the thought he does to Snape or Malfoy acting odd...). Junenal is right magic needs rules or there is no tension in the story, but honetly most of the time we don't need a bullet list of them.

Presumably the same same chapter from Hermione's perspective would include her actually listening to whatever information she was told and doubt thinking back to reading Veroda Johnson Time 'Turners a practical guide [Most secret press Ministry of Magic]'

More generally I am hard pressed to think of any time travel sequence in Fiction that does not have more problems than answers. Seeing as David Tennant was in one of the movies just remeber time travel is Whibbly wobbly timey whimey

* Just consider for example there actually is a reason in the LOTR why the Witch ling is so ominously powerful in the third book but so tentative in book one, but to get to that point JRRT would have had to cram at least 2 or 3 stories from Unfinished tales, part of the appendix and chunks of Silmarillion into the story.