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Blueberry comments on Diseased thinking: dissolving questions about disease - Less Wrong
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The requirement is not that there is no divergence, but that the divergence is small enough that no-one could notice the difference. Sure, if a superintelligent AI did a molecular-level scan five minutes before the hypothetical started it would be able to tell that there was a switch, but no such being was there.
And the point of the hypothetical is that the question "what if, counterfactually, Alice ordered the eggplant?" is meaningful - it corresponds to physically switching the molecular formation of Alice with that of Alice' at the appropriate moment.
I understand now. Sorry; that wasn't clear from the earlier post.
This seems like an intuition pump. You're assuming there is a way to switch the molecular formation of Alice's brain to make her order one dish, instead of another, but not cause any other changes in her. This seems unlikely to me. Messing with her brain like that may cause all kinds of changes we don't know about, to the point where the new person seems totally different (after all, the kind of person Alice was didn't order eggplant). While it's intuitively pleasing to think that there's a switch in her brain we can flip to change just that one thing, the hypothetical is begging the question by assuming so.
Also, suppose I ask "what if Alice ordered the linguine?" Since there are many ways to switch her brain with another brain such that the resulting entity will order the linguine, how do you decide which one to use in determining the meaning of the question?
I know - I didn't phrase it very well.
Yes, yes it is.
I'm not sure. My instinct is to try to minimize the amount the universes differ (maybe taking some sort of sample weighted by a decreasing function of the magnitude of the change), but I don't have a coherent philosophy built around the construction of counterfactuals. My only point is that determinism doesn't make counterfactuals automatically meaningless.
The elaborate hypothetical is the equivalent of saying what if the programming of Alice had been altered in the minor way, that nobody notices, to order eggplant parmesan instead of fettucini alfredo which her earlier programming would have made her to order? Since there is no agent external to the world that can do it, there is no possibility of that happening. Or it could mean that any minor changes from the predetermined program are possible in a deterministic universe as long as nobody notices them, which would imply an incompletely determined universe.
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Ganapati, the counterfactual does not happen. That's what "counterfactual" means - something which is contrary to fact.
However, the laws of nature in a deterministic universe are specified well enough to calculate the future from the present, and therefore should be specified well enough to calculate the future* from some modified present*, even if no such present* occurs. The answer to "what would happen if I added a glider here to this frame of a Conway's Life game?" has a defined answer, even though no such glider will be present in the original world.
Why would you be interested in something that can't occur in the real world?
In the "free will" case? Because I want the most favorable option to be factual, and in order to prove that, I need to be able to deduce the consequences of the unfavorable options.
What?
Not prove, implement. You are not rationalizing the best option as being the actual one, you are making it so. When you consider all those options, you don't know which ones of them are contrary to fact, and which ones are not. You never consider something you know to be counter-factual.
Yes, that's a much better phrasing than mine.
(p.s. you realize that I am having an argument with Ganapati about the compatibility of determinism and free will in this thread, right?)
Actually you brought in the counterfactual argument to attempt to explain the significance (or "purpose") of an approach called consequentialism (as opposed to others) in a determined universe.