The main form of prediction-impossibility he mentions is that our minds might depend meaningfully on quantum states, which are governed by the no-cloning theorem and therefore impossible even in principle to extract. Whether or not this is true is an open question, but the characterization of free will in terms of the concrete question "is it possible to build a prediction machine?" seems like a useful and novel contribution that doesn't just reduce to the old question of "is physicalism true".
That is, even if I could capture the relevant aspects of your mind state on a computer, i.e., the no-cloning theorem is not a barrier, it's still the case that the only way for me to predict what you will do in two minutes' time is to actually run your mind inside the computer for two minutes of subjective time. This would constitute a prediction machine in Aaronson's sense, assuming the computer could run faster than realtime. But since the computation that occurs is literally following your thought process step by step (Rice's theorem says there are no shortcuts), there's a real sense in which the decision was not determined until you -- the version inside the computer -- actually made it.
Of course this account depends on a functionalist/computational theory of mind, which can be quibbled with in all sorts of ways. But it does seem important for the philosophical discussion on free will to at least take into account the things we now know about the nature of computation, the character of physical law, and other scientific/mathematical questions, that were not known decades or centuries ago when the philosophical battle lines were being drawn. Yes, scientists can be arrogant and are often just wrong or deeply misinformed on philosophical questions. But that doesn't remove the responsibility of philosophers to engage with the frontiers of knowledge on these issues, which means engaging with people like Scott rather than just dismissing them as "confused". (as if anyone thinking about free will has ever not been confused!)
Right, I said that's probably all he should say.
>His point is that even if our actions are (probabilistically) determined by a set of underlying physical laws, it may still be that the character of those laws is such that it is fundamentally impossible to predict future actions, in which case we would still have meaningful free will.
It's hard to see how it makes any difference to my level of freedom whether someone else can successfully predict what I'm going to do. You can predict pretty reliably that I'm going to have breakfast in the morning, but it's still a free decision on my part.
>but the characterization of free will in terms of the concrete question "is it possible to build a prediction machine?" seems like a useful and novel contribution that doesn't just reduce to the old question of "is physicalism true".
It seems to me that the question of whether or not we have free well is largely orthogonal to the question of whether or not our actions are predictable. I suspect that all four combinations of predictable/unpredictable and free/unfree are logical possibilities. So I think Aaronson is conflating a lot of things that ought not to be conflated, and which have been endlessly and subtly picked apart in a philosophical literature that he appears not to have bothered reading. (I haven't read that much of it either, but it already contains pretty much every idea about free will that is likely to occur to anyone in our present state of knowledge.)
FWIW, I think Scott has read more of the philosophical literature on free will than probably anyone else in the world with a comparable level of quantum-physical expertise. If he's too confused to be allowed to discuss these issues, then what is the path by which philosophers expect to stay relevant and up-to-date with new knowledge? A field whose currency of legitimacy is "you must have devoted your life to understanding every detail of dispute in the existing literature" is not a living field that hopes to learn from outsiders and grow with new scientific inquiry. I think the best philosophers recognize this, and are willing to engage more broadly.
I’m a bit frustrated here, because physicists often seem to retreat to this position that it’s all just a question of terminology once people start pushing back against their philosophical claims. If Aaronson actually is using terms in such a weird way as you suggest, then I just have no idea what he is on about. We already have a perfectly fine word that means unpredictable; there’s no need to repurpose “free”.
I admit that I have no way of knowing what he has or hasn’t read, and my comment on that was snarky. But he doesn’t refer to any philosophical work in the interview, and I couldn’t find much published work by him that really engages with the current literature.
https://arxiv.org/abs/1306.0159
Scott is making a pair of claims: If it's possible to build a fast, noninvasive, perfect predictor then what more can science say to show that people don't have free will?
If it's impossible to build such a predictor, for some fundamental reason, then what more can science say to show that free will exists.
Before quantum mechanics and uncomputability, the "of course" went the other direction.
I think it's just sloppy discussion.
Any hard-determinist will say that every interaction is pre-determined based on a previous interaction. The compatibilist approach tries to reconcile hard-determinism with the illusion of free will in a reference frame of the individual - but I think falls apart. I think Aaronson is trying to convey this particular philosophy.
"if you knew the complete state of the universe, you could use it to calculate [either deterministically or probabilistically] everything I’d do in the future."
Fortunately for us, Godel explored this exhaustively and concluded (though did not prove) that this is not possible. See also the Munchhausen Trilemma of proofs for problems proving any epistemological inquiry.
[1]https://en.wikipedia.org/wiki/Hard_determinism
[2]https://en.wikipedia.org/wiki/Compatibilism
While I agree that Aaronson's take on philosophy is not very original or profound, I don't think that Gödel concluded anything of the sort, and if he said something in that vein (assuming you're referring to the discussion on mechanism in the link you're provided), it is more an expression of his faith that any problem can be solved (and since not every problem can be solved by a machine, the mind is more powerful than any machine) -- hardly a conclusion.
Downvotes or no it's worth saying. Defending any social science or humanity at all is hard work on a forum like this, but I think it's important.
I'd also have to say that Aaronson lacks imagination in a crucial respect. He claims that in any "imaginable" universe it will hold that "if you knew the complete state of the universe, you could use it to calculate [either deterministically or probabilistically] everything I’d do in the future." But of course it's very easy to imagine a universe where this is not the case. E.g., any universe where minds make free decisions that lack physical causes. We know that people have in fact imagined this sort of universe.