How is Harry able to cast the Patronus to save himself & Sirius?

Question

When we read about the Dementor attack down by the lake in Prisoner of Azkaban, we experience the situation twice. The use of the time turner affects both as both Harry's are present in both situations, we just see it from two different perspectives, first being before the use of the time turner when he believes he sees his father but is actually himself after using of the time turner.

What I don't understand is - the first time the Dementor attack ever happened there could not have been the version of Harry after the use of the time turner to cast the patronus in the first place. The problem lies it the fact that in order to get to the situation where Harry is able to use the time turner he requires there to be a version of himself which has already used the time turner - so if the Harry that used the time turner hadn't saved them, he wouldn't have been able to get into that position.

Presumably the Dementors would have succeeded in kissing him the first time so he wouldn't have been in a state to be able to use the time turner. Even though that is a presumption of what would have happened, the original part still doesn't make sense.

Answer 1

What you are describing is often called the bootstrap paradox, or a causal loop. Essentially, Event A causes Event B, then Event B leads to time travel to before Event A, and CAUSES Event A. From outside the loop, there appears to be no outside cause for the chain of events.

It is a fairly common trope in fiction involving time-travel. Best not to think about it too hard.

Answer 2

As @Himarm and @Irishpanda mentioned, it's time travel.

Presumably, in the Harry Potter universe, where there's the existence of time travel, the effects of the time travel are within the same timeline.

In pre-time turner, Harry and Hermione have already gone back to before Buckbeak was executed. The same 'sort' of thing happened there as well, Hermione tossed the rock that alerted the group to the incoming executioners.

Side Note: This kind of gives credence to the whole, "Why didn't anyone go back using a time turner and take care of Voldemort?" Well because if they had, it would have already happened.

Answer 3

The answer to this lies in how the book treats the timeline. Time travel as used in Prisoner of Azkaban seems to follow a one-pass method.

There are a few different ways of handling time travel in fiction, but for the purposes of this answer only one distinction is particularly relevant; that being, whether it is a one- or two-pass timeline.

A two-pass timeline is like that of Back to the Future. In a two-pass timeline, we first see the original, unaltered events, and then later see them in the second timeline with the changes enacted by the time travel.

A one-pass timeline is subtly different in that we are never shown the timeline that existed without the effects of the time travel, if it existed at all. One-pass timelines don't occur very often in fiction, as they can be quite confusing to the reader.

The trick here is that Rowling writes our first look at the scenes in question with our viewpoint from a distance, carefully obscuring the events. During the execution, the trio hear the swing and strike of the axe and Hagrid sobbing and draw the sensible conclusion, as do we as the readers. Then, when we learn about the Time Turner, we think that there is now the chance to go back and change the events.

What Rowling does masterfully here is trick us into thinking that we're looking at a two-pass timeline when it really is a one-pass timeline. The events of our first look at the timeline are actually perfectly consistent with the changed version; the axe still strikes, Hagrid still sobs, the Patronus is still cast, but the context we were missing the first time through leads us to believe that these were the 'wrong' events, that they have to be changed. It's only the second time we see the events that we realize that the actual events worked out just fine, and it was just our limited knowledge that made us think they needed to be changed.

So if you're trying to wrap your head around how Harry cast the Patronus the first time, instead try to make sense of this: there was never a version of that scene that didn't have both Harrys in it.

Answer 4

What I don't understand is - the first time the Dementor attack ever happened there could not have been the version of Harry after the use of the time turner to cast the patronus in the first place.

But that's not how it went down: the Dementor attack only ever happens once.

There has 'always' been a second Harry that sprung into existence shortly before the originals travel down to Hagrid's while carrying memories of events that have not yet happened. The existence of the second Harry is later explained when the original makes use of the time turner.

By using the time turner, Harry and Hermione did not change anything — it simply explains how events could have happened as they did.

Answer 5

Because JKR use a deterministic approach to time travel ( at least in this instance ). You have to imagine that the time flows in a straight line which can't be changed, so everything that happens is already written and meant to happen. The Harry who calls his Patronus always existed to call his Patronus for the other Harry.

On the other hand there is the non-deterministic approach, you see this in Back to the Future. Here the time flow may branch and each action is not pre-written. You see Marty go back and forth in time and each time he interacts with something (leave back the sport book). The future changes reflecting different branches of the flowing of time.

Answer 6

A lot of the answers here go along the "it doesn't make sense" and "best not to think about it too much" lines. If it hurts to think about it, then yes, just enjoy it! But there is a way of thinking about it that makes (a sort of) sense.

The many worlds interpretation of quantum mechanics states that every decision we make results in a new universe being created. If we reach a fork in the road and decide to turn left, then we create a universe which represents that decision - but another universe is created in which we turn right, so both outcomes actually occur.

How does this help? Well, when Harry makes his decision to use the time-turner, he is creating two universes, one in which he used it, and one in which he didn't. In the one where he didn't, he never went back and stopped the dementors. But in the one where he did, Harry is saved. The point is that that "possibility" wasn't made real until Harry used the Time Turner. The Harry that was saved, was saved because that was the decision that created that universe (and therefore timeline).

Having said all this, this explanation probably doesn't help that much. Quantum Theory comes with its own set of bewilderments and counter-intuitions. But it is real, testable and pretty much right, in terms of its ability to explain what happens in nature. Further reading:

http://www.preposterousuniverse.com/blog/2014/06/30/why-the-many-worlds-formulation-of-quantum-mechanics-is-probably-correct/

or just google Many worlds interpretation.