Why does Chalmers' argument not entail some form of idealism?
I just read the page, and there is certainly no hint of idealism involved. That would imply that Chalmer's idea involves mental ontology, a sort of rejection of physicalism. Rather, his theory is particularly physicalist; you will notice that he politely turns away from any spiritual, supernatural explanations for experience (the focus of his "hard problem of consciousness") and rather tries to develop a physicalist-compatible explanation.
I will try to explain the general ideas involved, and in doing so show that these ideas are very physicalist and empirically oriented. Therefore, they do not address idealism at all but as we shall see, physicalism and a sort of dualism.
Chalmer rejects reductionist attempts at explaining the problem of experience, and rather suggests that we use a non-reductive (but physical) approach; perhaps experience itself is something fundamental. Perhaps it is some property of our physical world that is not explained by anything else because it just is itself.
This is much like our models of the electron and other fundamental particle - we do not seek to explain what makes up an electron (as of yet, it just appears to be a point particle), but just accept it as something that cannot be reduced. This is the gist of Chalmer's theory, and demonstrates that he approaches the problem with a focus on physicalist explanations; this is quite incompatible with idealism, as he is arguing that the world itself has some fundamental property (particle?) called experience, and it is not part of the human mentality.
Is he really advocating some form of dualism?
Yes! In fact, he explicitly admits it:
This position qualifies as a variety of dualism, as it postulates basic properties over and above the properties invoked by physics. But it is an innocent version of dualism, entirely compatible with the scientific view of the world. Nothing in this approach contradicts anything in physical theory; we simply need to add further bridging principles to explain how experience arises from physical processes. There is nothing particularly spiritual or mystical about this theory - its overall shape is like that of a physical theory, with a few fundamental entities connected by fundamental laws. It expands the ontology slightly, to be sure, but Maxwell did the same thing. Indeed, the overall structure of this position is entirely naturalistic, allowing that ultimately the universe comes down to a network of basic entities obeying simple laws, and allowing that there may ultimately be a theory of consciousness cast in terms of such laws. If the position is to have a name, a good choice might be naturalistic dualism.
This "naturalist dualism" is Chalmer's explanation for experience. As explained above, he believes in the physical nature of the world and experience itself. Thus, he is certainly not conveying some form of idealism, nor a "spiritual or mystical" dualism. His version of dualism is quite physicalist, perhaps unlike other more familiar versions.
Since he wants a physicalist explanation, one maybe a little empirical unlike most dualist theories, he seeks to attribute all phenomena - in this case, that of experience - to the physical. This answers your question:
Why even worry about deriving consciousness & experience from the physical?
As to your side note:
What is the meaning of the sentence beginning "It is conceptually coherent..."? If by that he means that it is obvious that physical processes do exist in the absence of experience or consciousness, then what is the evidence for that?
I agree with your interpretation of the line, and I'll offer an example: in the absence of experience or consciousness, would a rock fall? Surely this is a physical process. I think that the statement itself can be interpreted two ways:
- An object that has no consciousness or experience (has an absence of them) can experience physical processes. A rock has neither consciousness or experience (at least, we're pretty sure it doesn't) but the physical process of falling is definitely "instantiated" within it.
- An object that is not observed by an instance of consciousness or experience can experience physical processes. This seems like another version of "if a tree falls in a forest and there's nobody around to hear it, does it make a sound?" Admittedly, this is by definition not empirically provable (unless it counts if you can record the event and watch later). However, given all we know, it seems very likely that the tree will make a sound, and that even in the absence of our experience, objects will undergo physical processes.
