[HPforGrownups] Time-turning (Was: World Building And The Potterverse)

[Jordan Abel]

No: HPFGUIDX 167400

>Dave:
> This is okay for something like "A Christmas Carol", where the
> characters are passive observers, but you *still* cannot have a
> "closed timelike loop" without creating a paradox of causality. An
> example of a "closed timelike loop" is Harry going back in time to
> save himself from the dementors, so that later he can go back in time
> to save himself from the dementors.

Random832:
A paradox would be if he went back in time and killed his past self,
i.e. something that _cannot_ resolve in a self-consistent manner. (there
are various principles for dealing with this, my favorite is the Novikov
self-consistency principle, the idea that the probability of anything
that would contradict itself vanishes to zero, and the resolution of any
time-travel event happens in a quantum probabilistic manner. you might
not be familiar with the various ideas that exist in this area of SF,
since you, as you said, don't like time travel and have largely, if
unintentionally, avoided it.)

And there are no closed timelike loops involved. A closed timelike loop
is when a single object sent back in time from (say) 5:00 to 3:00 _is_
its own past self, never existed before 3:00, and doesn't exist after
5:00.

Your problem seems to be with the fact that it could just as easily have
resolved as Harry being killed by Dementors and no-one ever going back
in time. But the selection between those resolutions is completely
arbitrary, and even if one is more probable than the other, improbable
things do happen randomly on a quantum level.

> Dave:
> There's only two ways that I see to resolve the paradox, both of
> which are problematic:
>
> 1. Everything in the Potterverse is predetermined from the
>    Creation onward, [...]

I don't think full predestination is necessary for Novikov to apply;
you're taking an all-or-nothing approach here. It's sufficient for the
universe to simply have a constraint against inconsistency, and anything
not inconsistent may happen based on free will etc.

> Dave:
> 2. There was a second Patronus-caster behind the grassy knoll(!)
>    to initially save Harry's life, before he goes back in time to save
>    himself.  But then the question is, WHO?? [...]

Random832:
Again, you're insisting that "time happened twice" - Future!Harry _is_
the patronus-caster behind the grassy knoll.

> Ken:
> But then I discovered that this other book about how the South won the
> Civil War involved no time travel, only three cigars and a piece of
> paper. I've been reading Harry Turtledove's alternate historys ever
> since, but only the ones that deal with plausible departures from
> reality.

What about the series (i forget the title) by him that deals with these
but use some ridiculous interdimensional travel as a framing device?
What do you think of those?

> Ken:
> The Harry who we are to believe is his own salvation could throw the
> Potterverse into a meltdown by simply refusing to go back, or to cast
> a Patronus. That's a very odd way to run a Potterverse, in my opinion.

Random832:
Except he doesn't know any of this. And that is the key here - if he
did, there would be a risk of that - if nothing else he might _fail_ to
cast Patronus due to overconfidence or whatever.

> Dungrollin:
> Harry jumped back and lived three hours over again, but he never
> jumped forwards, so he is now three hours older than he should be.
> Does this mean that the blood protection will expire three hours
> earlier than Harry thinks,

Random832:
I love it! Though, I've been thoroughly unimpressed with the "blood
protection" thus far. We only see it undisputedly in action once, in PS,
and we have a very good reason to think that it's _gone_ as of GOF.

> Dungrollin
> Thinking it could just as easily be ESE!Lupin who spilled the beans...

--Random832; that, not so much.