time travel in PoA

[qaztroc]

No: HPFGUIDX 41940

--- In HPforGrownups at y..., "Amanda Geist" <editor at t...> wrote:
> 
> Buckbeak was already saved because H&H *did* go back in time--even
if they
> don't know this yet. Dumbledore knew that Buckbeak had to be part of
the
> equation, so he was giving H&H a clue, so that when they did go
back, they'd
> be able to figure it out. So Buckbeak *was* the other innocent life
to be
> saved.
> 
> Dumbledore, from his perspective (knowing that Buckbeak apparently
> disappeared, suspecting it's more), knows that H&H have to involve
Buckbeak.
> Yes, when he makes this statement, the saving of Buckbeak has
already
> occurred. However, the action which saves him will be H&H's *future*
action
> (viewed from their perspective). He's giving them a hint, to help
them take
> the action, once they have used the Turner, that he knows has
already
> happened.
> 
> Okay, that made sense when I typed it....did anyone follow it?
> 
> --Amanda


Hello all! I am new to this group. Being an astrophysicist, 
I have some training in figuring out things like time-travel, 
so I thought I should join in the discussion.

There are two different *physically consistent* solutions
of the infamous time-paradox problem of time travel. One is the
"Parallel Universes" hypothesis, the other one is the "Single 
Unchangeable Universe" hypothesis. Sorry for the jargon, but 
it's very simple, really!

In the "Parallel Universes" hypothesis you can consistently go
back in time and actually change things. However, whenever you
do so you are actually move to a different Universe, one where
the sequence of events is different from the one you come from.
The big problem with this solution is that while you really can 
change things in the past, it really is impossible to *influence
future events* by going back in time and change things. Let me 
illustrate this point in PoA. Assume that Buckbeak has actually been 
executed, and that Dumbledore sends H&H back in time to save Buckbeak 
and free Sirius. If they succeed in saving Buckbeak, this means that
they've actually travelled to a parallel Universe, in which Buckbeak
is not executed. Now that would be silly from Dumbledore's point of 
view, because it is now impossible for H&H to save Sirius in the 
Universe he's in: H&H are simply gone (for good?) in a different
Universe, and Sirius will get the dementor's kiss anyway. The fact 
that Sirius may be freed in another Universe is of no consequence in
the Universe Dumbledore is in at the moment he sends H&H back in time.

In the "Single Unchangeable Universe" hypothesis, you can still 
travel back in the past if you want, but there exists only one
sequence 
of events, and it is *absolutely impossible* to change it. This 
means that if you go back in time and attempt to change an event you 
know had occured, you  will necessarily fail! Now, I am under the 
impression that JKR's scenario follows to the "Single Universe" 
hypothesis, and her story is consistently (and beautifully!) 
structured with that in mind. As many of you have pointed out 
already, the best interepretation is that there is only one 
sequence of events: Buckbeak is never executed in the first place 
because H&H have traveled back in time to save him, save themselves 
from the dementors, and free Sirius. No event is changed by H&H's 
use of the time-turner, everything simply occurs consistenly.

Now why Dumbledore's subtle hint? First, why wouldn't he be more 
explicit, and just tell them to go and save Buckbeak and use him to 
free Sirius? Well, because Dumbledore really *doesn't know for sure* 
that H&H are responsible for saving Buckbeak. If they're not, then by
being too explicit about what they should do he risks sending them 
on a wild goose chase: they would fail in saving Buckbeak themselves
because H&H absolutely cannot change events! On the other hand, why 
give them any hint at all? If H&H are indeed responsible for
Buckbeak's escape, isn't that what they're going to do anyway? No 
need to tip them off!

I think Dumbledore knows that time-travel is not about changing past 
events, so he is really gambling on what he thinks the actual sequence
of events is. The biggest gamble is on what his own role should be! 
So he talks and acts very carefully, only suggesting some course 
of action, instead of sending H&H on a mission. The very subtle
intervention of Dumbledore reveals the full magnitude of his genius.

=====
Qaztroc