what’s the point of imagining a hypothetical set of physical laws that lack internal coherence?
I don’t think they lack internal coherence; you haven’t identified a contradiction in them. But one point of imagining them is to highlight the conceptual distinction between, on the one hand, all of the (in principle) externally observable features or signs of consciousness, and, on the other hand, qualia. The fact that we can imagine these coming completely apart, and that the only ‘contradiction’ in the idea of zombie world is that it seems weird and unlikely, shows that these are distinct (even if closely related) concepts.
This conceptual distinction is relevant to questions such as whether a purely physical theory could ever ‘explain’ qualia, and whether the existence of qualia is compatible with a strictly materialist metaphysics. I think that’s the angle from which Yudkowsky was approaching it (i.e. he was trying to defend materialism against qualia-based challenges). My reading of the current conversation is that Signer is trying to get Carl to acknowledge the conceptual distinction, while Carl is saying that while he believes the distinction makes sense to some people, it really doesn’t to him, and his best explanation for this is that some people have qualia and some don’t.
I don’t think they lack internal coherence; you haven’t identified a contradiction in them. But one point of imagining them is to highlight the conceptual distinction between, on the one hand, all of the (in principle) externally observable features or signs of consciousness, and, on the other hand, qualia. The fact that we can imagine these coming completely apart, and that the only ‘contradiction’ in the idea of zombie world is that it seems weird and unlikely, shows that these are distinct (even if closely related) concepts.
This conceptual distinction is relevant to questions such as whether a purely physical theory could ever ‘explain’ qualia, and whether the existence of qualia is compatible with a strictly materialist metaphysics. I think that’s the angle from which Yudkowsky was approaching it (i.e. he was trying to defend materialism against qualia-based challenges). My reading of the current conversation is that Signer is trying to get Carl to acknowledge the conceptual distinction, while Carl is saying that while he believes the distinction makes sense to some people, it really doesn’t to him, and his best explanation for this is that some people have qualia and some don’t.