Harry tested whether you could make something weird happen by drinking the tea, not whether you could make someone drink the tea when you did something weird, subject to you not yourself knowing what would be weird enough before you saw them drinking.
I have refined my idea based on some re-reading. I forgot that you aren’t guaranteed to choke on every sip. Someone let me know if the following is too farfetched.
As you said, when something shocking is going to happen, someone with access to the tea feels an impulse to drink it. Now recall this line from chapter 7, not given much thought to by Harry:
“It doesn’t always happen immediately,” the vendor said. “But it’s guaranteed to happen once per can, or your money back.”
So translating to the backwards-causation hypothesis, if nothing shocking is going to happen before you finish drinking the can, the tea stops you drinking it.
OK, let’s put this together with the idea that time-reversed causation preserves self-consistency. I deduce that if you sit someone down in front of a glass of Comed-Tea for lunch they will start drinking from it only if they will be shocked enough to choke on it at some point. So what you do is resolve to take the ‘water’ away if your lunch-mate drinks from it and does not splutter. The Comed-Tea enchantment, by self-consistency, will ensure that this never actually happens, so you can now be certain that if your buddy raises his glass and starts to sip, he will choke.
Now you do what I suggested and run through your guesses. If your buddy raises his glass, you know that what you’re about to say will be shocking. If he doesn’t, you don’t bother saying it. We know that Comed-Tea creates a strong impulse to drink it when one is about to be shocked, so your buddy, not knowing what he’s drinking, is a sure bet to drink it if he is in fact about to be shocked. The only part of my idea that is now in question is this: if your resolve to do something shocking is conditional only on him drinking the tea, and his drinking the tea is conditional only on your being about to do something shocking, will he drink the tea in response to your commitment, given that your possible action is in fact shocking?
A causes B; B causes A. Do A and B both occur, or do neither? That’s exactly the same question that occurs to Harry when he gets the Time-Turner. And that in turn makes me think that I’m missing something, because it can’t be the case that all temporally self-consistent A-B pairs happen. Any ideas?
Unfortunately, there’s nothing that says the tea will force your lunch-mate to drink on the first thing you think about that would cause him to choke. You could run through a dozen true and shocking guesses in your head without him feeling any urge to drink. Once you get bored and give up thinking of new hypotheses, if your lunch-mate hasn’t drunk from the can, the vendor’s guarantee is still intact because none of the the tea has been drunk. Why does this remind me of the halting problem?
On the other hand, if you wait until after your lunch-mate has taken his first sip (taking the risk that something unexpected and shocking will happen when he does so), and you have resolved to take away the drink immediately after his second sip, you might be in a better position.
You also need to hope that the shocking event that causes your companion to choke is not an epiphany on his part where he suddenly deduces one of your secrets.
That does seem like it may just work. It is also a case where TDT comes in handy. Causal reasoning would suggest that once you have already got your answer there isn’t any reason to actually make the scene (which could potentially give away your strategy.)
There are some limitations on working out whether the ‘weird’ is ‘good guesswork’ specifically but it certainly gives you some strong evidence.
I wonder about that “or your money back” part. Was it added because the causal charm did not always work or “in order to” make it not always work? What if a wizard found himself very thirsty in a desert, incapable of Apparating and having only the tea to support him? It would be torture.
So what you do is resolve to take the ‘water’ away if your lunch-mate drinks from it and does not splutter.
I don’t think that the vendor will apply the guarantee in that case. Next you’ll forget about messing with causality and just try to get your money back by opening the can and pouring the contents away. Surely the guarantee only applies if one finishes drinking it!
Harry tested whether you could make something weird happen by drinking the tea, not whether you could make someone drink the tea when you did something weird, subject to you not yourself knowing what would be weird enough before you saw them drinking.
I have refined my idea based on some re-reading. I forgot that you aren’t guaranteed to choke on every sip. Someone let me know if the following is too farfetched.
As you said, when something shocking is going to happen, someone with access to the tea feels an impulse to drink it. Now recall this line from chapter 7, not given much thought to by Harry:
So translating to the backwards-causation hypothesis, if nothing shocking is going to happen before you finish drinking the can, the tea stops you drinking it.
OK, let’s put this together with the idea that time-reversed causation preserves self-consistency. I deduce that if you sit someone down in front of a glass of Comed-Tea for lunch they will start drinking from it only if they will be shocked enough to choke on it at some point. So what you do is resolve to take the ‘water’ away if your lunch-mate drinks from it and does not splutter. The Comed-Tea enchantment, by self-consistency, will ensure that this never actually happens, so you can now be certain that if your buddy raises his glass and starts to sip, he will choke.
Now you do what I suggested and run through your guesses. If your buddy raises his glass, you know that what you’re about to say will be shocking. If he doesn’t, you don’t bother saying it. We know that Comed-Tea creates a strong impulse to drink it when one is about to be shocked, so your buddy, not knowing what he’s drinking, is a sure bet to drink it if he is in fact about to be shocked. The only part of my idea that is now in question is this: if your resolve to do something shocking is conditional only on him drinking the tea, and his drinking the tea is conditional only on your being about to do something shocking, will he drink the tea in response to your commitment, given that your possible action is in fact shocking?
A causes B; B causes A. Do A and B both occur, or do neither? That’s exactly the same question that occurs to Harry when he gets the Time-Turner. And that in turn makes me think that I’m missing something, because it can’t be the case that all temporally self-consistent A-B pairs happen. Any ideas?
Unfortunately, there’s nothing that says the tea will force your lunch-mate to drink on the first thing you think about that would cause him to choke. You could run through a dozen true and shocking guesses in your head without him feeling any urge to drink. Once you get bored and give up thinking of new hypotheses, if your lunch-mate hasn’t drunk from the can, the vendor’s guarantee is still intact because none of the the tea has been drunk. Why does this remind me of the halting problem?
On the other hand, if you wait until after your lunch-mate has taken his first sip (taking the risk that something unexpected and shocking will happen when he does so), and you have resolved to take away the drink immediately after his second sip, you might be in a better position.
You also need to hope that the shocking event that causes your companion to choke is not an epiphany on his part where he suddenly deduces one of your secrets.
That does seem like it may just work. It is also a case where TDT comes in handy. Causal reasoning would suggest that once you have already got your answer there isn’t any reason to actually make the scene (which could potentially give away your strategy.)
There are some limitations on working out whether the ‘weird’ is ‘good guesswork’ specifically but it certainly gives you some strong evidence.
I wonder about that “or your money back” part. Was it added because the causal charm did not always work or “in order to” make it not always work? What if a wizard found himself very thirsty in a desert, incapable of Apparating and having only the tea to support him? It would be torture.
I don’t think that the vendor will apply the guarantee in that case. Next you’ll forget about messing with causality and just try to get your money back by opening the can and pouring the contents away. Surely the guarantee only applies if one finishes drinking it!