Who conjures the Prongs Patronus?

[drtruman]

No: HPFGUIDX 53361

GulPlum wrote:
> 
> The fact is that everything that Harry2 and Hermione2 made happen, 
happened in the original timeline. Heck, I''m confusing myself now. 
There isn't an "original timeline". There is only *ONE* timeline, in 
which for three hours, there were two Harrys and two Hermiones.
> 
> Harry1 and Hermione1 didn't know that their duplicates were 
skulking around - like the principled people they are, they abided by 
the rules and aren't seen. However, Harry2 *was* seen (by Harry1), 
and it was when Harry2 realised that what he'd seen earlier (as 
Harry1) was himself, and not his dad, that he knew that the timeline 
consisted of him showing himself to cast the Patronus. He therefore 
showed himself and cast the Patronus (as he explains to Hermione2 as 
soon as he's done it).
> 
> If you want to think about it in terms of temporal (meta)physics, 
yes, there's a causal loop in place: Harry2 has to save Harry1 in 
order for Harry1 to survive and become Harry2 who saves Harry1... 
(and so on, ad infinitum).
> 
> However, if you forget about the fact that time travel permitted 
all of this to happen and realise that there is only one, single 
timeline, in which one iteration of Harry saved another, you don't 
need to worry yourself with temporal (meta)physics.

Thanks to all who have responded to my post. I think I have finally 
figured it out, in a way that makes sense to me, and the logic of 
which I accept. GulPlum gets credit (via his earlier post on this 
subject) for ultimately making the lightbulb go on over my head -- 
for which I thank him, and say I hope your headache is better!

Just to make sure I'm getting it: I had been framing the issue in 
terms of: how does Harry1 survive in order to come back as Harry2 to 
be able to save Harry1. The real issue becomes: what happens if 
Harry2 *doesn't* save Harry1 (say, he just sits there waiting in vain 
for dear ol' Dad to show up and cast the Patronus)? Then, if I'm 
getting this right, *that's* what would alter the reality, and *both* 
Harrys would cease to exist, or perhaps only Harry2, and Harry1 would 
exist only as the shell of himself that would result from a 
successful Dementor's Kiss.

Is that about right?
DR Truman