time turner question - PoA

[allies426]

No: HPFGUIDX 88593

Okay, I know that this must have been discussed when PoA 
came out, but I am having trouble with the archive search...  

When Harry, Hermione, and Sirius collapse fending off the 
dementors around the lake, and Harry sees someone on the 
opposite shore fire off a Patronus and chase the dementors 
away, how could it be that he was seeing himself???  He and 
Hermione HAD TO survive that attack without a "Harry from the 
future," because if they didn't survive it, there would be no "Harry 
from the future" to save them.  (I have this same issue with 
Terminator 2... how can you get the idea for a microchip from the 
microchip that you haven't invented yet?  But I digress...)  Since 
he had to go through that experience before he and Hermione 
went back in time... who created the Patronus the first time?

If this has been discussed at length (which I'm sure it has), can 
someone point me to the thread?  Thanks.  :) 

Even with the Time-Turner problem, it's still my favorite of the 
books!

Allie