Time Travel and Chuck Berry

[Robert Jones]

No: HPFGUIDX 91868

Troels Forchhammer in post 91756 responded to how my question of how 
time-traveling Harry could produce a Patronus:
> 
> Harry had seen himself do it - once he realised that the person
> he saw by the lake was himself, he also knew with absolute 
certainty
> that he had indeed seen himself cast the Patronus Charm.
> 
Bobby:
I still do not understand.  At first, both old Harry (Harry1) and 
time-traveling Harry (Harry2) do not have the confidence to produce 
a Patronus.  He (Harry1) does not realize that he (Harry2) produced 
it.  At first time-traveling Harry (Harry2) does not have confidence 
either, but he has time to realize that he (Harry1) saw him (Harry2) 
produce a Patronus, and so he (Harry2) now has the confidence to do 
it.  But this is like the Chuck Berry paradox from the movie "Back 
to the Future" where the Michael J. Fox character learns Chuck 
Berry's guitar licks off Chuck's records but then teaches Chuck 
those same licks over the telephone — so Fox learns the licks from 
Berry who learns them from Fox, and so on, and so on.  In effect the 
earlier Chuck Berry learns his licks from the future Chuck Berry.  
So there is no point in this loop for Chuck to actually create the 
licks.  And the same problem applies to Harry: Harry2 can make a 
Patronus because Harry1 saw him already do it because Harry2 did it 
because Harry1 saw . . .  At no point in the loop can Harry2 gain 
the confidence to produce the Patronus.


Second, Troels Forchhammer responded to me saying that JKR permits 
time-travelers to change history:

> I prefer to believe Hermione's information wrong rather than accept
> an internal inconsistency (allowing changes to the past would 
create plot-holes large enough to pass not only Hannibal and his 
elephants through, but the Alps as well). That is merely a matter of 
personal
> priority.

Bobby:  But my point is that JKR accepts that time-travelers can 
change history and so if she uses it again she can do whatever she 
wants to the plot (and that makes it a crumby plot device).