While discussing Harry Potter and the Prisoner of Azkaban with me, my roommate Jordan mentioned that there was an irreconcilable paradox presented in the book. The story is as such: Harry is about to have the life sucked out of him by the dementors when a powerful wizard across the lake casts a hefty patronus spell to ward off the dementors. In his fleeting moments of consciousness, Harry believes that it was his now-deceased father who appeared and cast the spell.
Later, Harry and Hermione travel back in time to save “more than one” life. Harry of the Future eventually finds himself across the lake, watching Present Harry getting succumbing to the dementors. He tells Hermione that his father is bound to appear any moment to invoke the patronus. However, at the last critical moment, Future Harry himself steps up and wards off the dementors, thus saving his own life.
Up until that point, Harry had been able to produce only a very feeble patronus. He later states that at the last minute he knew he could do it because he had seen his own patronus. Thus, disaster is averted, and all ends well.
I might point out a few–shall we say–internal difficulties this plot presents. Of course Future Harry knows the future of Present Harry, but in his confidence-building realization that he had seen his own patronus, we realize that Present Harry across the lake had witnessed the future of Future Harry. In other words, in that moment of clarity, Present Harry encountered Future Harry’s future, and that gave Future Harry confidence to act. I’m still struggling to get my mind around this, but it seems ironic to say the least that Present Harry (who had not yet time-travelled) could have any insight about the future. This is probably why the professor wisely told Michael J. Fox to avoid himself in Back to the Future.
Another paradox arises, and this is the fact that Harry could create a powerful patronus because he had seen himself do it. This is a classic chicken-and-egg scenario. Which came first, Harry’s patronus or his confidence?
Lastly, and this is where things really break down, it is clear that Future Harry saved Present Harry’s life. Future Harry could only travel back in time because Present Harry had lived. Had Present Harry died, there would be no Future Harry. In other words, Present Harry’s living depends on Future Harry’s acting which in turn depends on Present Harry’s living. If this were a choose-your-own-adventure book, this branch of the plot is dependent on that very branch curving back on itself and inserting a branch point. (Sorry for the mixed metaphor.) I suppose this may be J.K. Rowling’s implicit argument for a divine presence, but I think it would be much more intellectually satisfying had Future Hermione saved Present Harry’s life.
For those who do not find this discussion compelling, perhaps you will be deeply moved by this Prohibition Era photograph.