“It is clear that there is no more of a conceptual entailment from biochemistry to consciousness than there is from silicon of from a group of homunculi…. So consciousness fails to logically supervene on the physical.”
Chalmers is suggesting that consciousness can't be reduced to a physical structure or property because the silicon model of neural circuitry is functionally identical to biochemical neural circuitry, yet the silicon model can't exhibit consciousness. This is an assumption that silicon and neural circuits are identical... but I would contend that there is a “conceptual entailment from biochemistry” that provides a physical property on which consciousness may very well supervene.
The difference between a silicon and neural circuit is plainly that the former is closed and the latter is open... such that the electrical flow of messages through each respective circuit may occur in the same phenomenological fashion, but not the same physical fashion. Namely, when circulating an electrical signal, a closed circuit releases energy only in the form of heat, whereas an open circuit releases energy as mostly Gibbs free energy with the ability to do work, and very little heat. A silicon circuit is not self propagating, namely, through its path it meets only with resistors and inductors which cause it to dissipate heat. However, a neuronal signal is self propagating, and free energy in its environment is both consumed and produced by that process. This, of course, is assuming that energy and heat are physical properties on which consciousness might supervene. Since the free energy has the capacity to perform work, and heat does not, the neural circuit is the one with the ability to support consciousness.
Because free energy is undefined aside from its ability to do work, it is possible that this particular physical property is the medium through which neural structure and consciousness are connected. Therefore, I propose that the changes in free energy that occur during electrical signal propagation in a neural circuit may be the physical cause of consciousness. Free energy, being the physical difference between a neural and silicon circuit, would explain consciousness arising in one and not the other, and provide a physical property to which consciousness might be reduced.
But all this... is written out of fear. If humans manage during my lifetime to find the physical matter of consciousness such that we can replicate it... my soul will crumble, and my fascination with the human condition will suffer a dreadful, murderous demise. As a neurochemist, I need for there to be some manner of correlation between biochemistry and consciousness. As a mind, I need for that matter to be untouchable, and irreplicable.