Eliezer_Yudkowsky comments on Harry Potter and the Methods of Rationality discussion thread, part 5 - Less Wrong

6 Post author: NihilCredo 02 November 2010 06:57PM

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Comment author: Eliezer_Yudkowsky 02 November 2010 08:49:08PM 3 points [-]

Azkaban's future cannot interact with its past.

Comment author: Unnamed 02 November 2010 09:18:03PM 5 points [-]

McGonagall and the other two Harrys aren't in Azkaban, so don't see why that fact would make her Patronus go to the Harry that is in Azkaban.

Comment author: wedrifid 02 November 2010 09:27:25PM 1 point [-]

WTF. There are multiple Harry's now? Wow, I must catch up on the recent chapters!

Comment author: JGWeissman 02 November 2010 09:34:21PM 33 points [-]

Yeah, he suffers from spontaneous duplication, which is being treated by his spinster wicket.

Comment author: bogdanb 03 November 2010 11:20:04AM 3 points [-]

I get this as meaning you can’t use the Time-turner inside Azkaban. I’m not sure if this is relevant to the story, but could one “duplicate” himself (or more) outside Azkaban, and then get all copies inside it? E.g., go to Azkaban, get out, go back to before entering Azkaban, and enter again? Are you forbidden to go back in time over a period you were in it, or is your copy prevented from approaching, or what?

Comment author: DaveX 03 November 2010 04:02:17PM *  12 points [-]

A copy with knowledge of a Azkaban at a certain time seems forbidden from approaching/entering Azkaban at a prior time. See "Azkaban's future couldn't interact with its past, so she hadn't been able to arrive before the DMLE had gotten the message," in Ch55. The restraint isn't so much when the DMLE gets the message, it's when Azkaban sends the message. It can't send a message that affects its past.

Azkaban might be a good place to try a can of Comed-tea.

Comment author: bogdanb 16 November 2010 04:02:36PM 1 point [-]

You’re right, I had forgotten that passage.

I’m still curious how it actually works. The portal she used could simply refuse to work, but how would you be prevented from simply walking in? An invisible wall you can’t walk through, or just a sequence of increasingly improbable events happen that keep stopping you?

(If Harry’s explanation of how Comed-tea is right, it probably means just that you won’t get the urge to drink it. That “or your money-back” line suggests that you can drink it without a result, presumably if you figured it out. Though the charm might also inhibit your wanting to drink it when nothing will happen; otherwise, there would be a lot of unsatisfied customers who drank it just because it was hot and they were thirsty. If it does, you might not get the idea to test it.)

Comment author: [deleted] 04 November 2010 05:27:16PM 2 points [-]

This must mean that when Harry's Patronus knows that another Patronus is looking for it, it isn't because Harry, say, went back in time and sent himself a Patronus message. (Which would have been problematic on its own: where would the information have come from in the first place? It'd be a stable loop with no reason to exist, and I'd like to think such things don't happen.)

So either someone who has non-time-travel knowledge of Dumbledore's actions sent this message to Harry (and who could have done this?)...

or his Patronus knows this on its own, and it isn't a message after all.

The first option is unlikely, but I am confused by both options. A Patronus isn't actually that intelligent is it? And even if Harry's Patronus is, how would it know that another Patronus is looking for it?

Comment author: DanielLC 05 November 2010 05:20:02AM 2 points [-]

where would the information have come from in the first place?

The same place where "Don't mess with time travel" came from.

Comment author: [deleted] 06 November 2010 11:00:36PM 2 points [-]

I have a theory about that, actually. If the experiment had gone just as Harry expected, would he have been able to avoid the temptation to write something different on the paper, just to see what happens?

Quite possibly the only stable time loop was one which involved a sufficiently creepy experimental result.

Comment author: shokwave 08 November 2010 03:05:35PM 4 points [-]

My pet theory was that Harry wrote "Don't mess with time" to himself because in a previous iteration, he had succeeded in using Time Turners to quickly factorise, and then parlayed this capability into a money-making scheme; shortly followed by a world takeover-cum-ascension to godhood, realised it was overall a bad thing, had one of his "this is that moment twenty years from then where I look back and point to exactly where it went wrong" moments, and used his power to return to that time, complete with the knowledge that he shouldn't mess with time. Which leads to him writing "DO NOT MESS WITH TIME" down, which leads to him seeing that, realising none of this, but writing down "DO NOT MESS WITH TIME" with the same level of fear and thus the same hand-shakiness, and thus we get a stable loop.

I would like to point out that this theory is both more consistent with the evidence available to us from the story, and more consistent with what we know about Eliezer: that a world that simply cheats is aesthetically unpleasing; and that it would amuse him to hide this from us.

Comment author: Randaly 05 November 2010 04:01:32AM 2 points [-]

Patroni are sentient!