In principle it's detectable. Instruments for doing so are improving.
Absolutely. They have even had success with questionnaires to patients in comas, based off of reactionary brain activity. But we have to always remember what the claim of Physicalism is, that there is nothing about ultimate reality that is beyond the explanation of physics.
We claim that the brain activity of the coma patient explains the thoughts/feelings of a mixture of joy & sadness whenever we play her wedding song because it activates brain states A, B, C, and D. And we know this because we have a mountain of data from coherent test subjects who confirm that a joy & sadness mixture of thoughts/emotions in them also fires off brain states A, B, C, and D
But the problem is that it seems obvious to us only because we all have experience with the phenomena of a joy & sadness thought mixture, and this very real phenomena of the experiential feeling of joy/sadness doesn’t really need clarification from anyone because we all intuitively understand it, so it’s very easy to just lump the experience and the brain states together and call it a day.
But they are not the same thing. Data from Star Trek is completely confused about what this experiential feeling thingy is that everyone keeps talking about, he doesn’t have the luxury of making the obvious connection between the two due to experiential instances to draw from. Data however can run circles around all of us when it comes to grasping the most minute physical details of the brain states involved in a joy & sadness mixture because he is what the Physicalists would probably refer to as “The philosopher par excellence” because of his extraordinary comprehension of physics. The only major problem is that he doesn’t get it. This concept of an emotional joy & sadness mixture is not something he has access to, because access to this phenomena is off of the radar of physics. So it turns out that physics can not exhaustively describe anything that there is to describe in ultimate reality.
However the same kind of distinction exists with computers. Execution of a program isn't something that it's easy to detect with physical measurements, except as it produces outputs. In principle it's possible, but with modern chips it would be nearly impractical.
Well something being difficult to determine/detect/comprehend, etc, is very different than the claim that there is nothing there at all that can be physically detected. I disagree with reductive physicalism but I still think that the theory has a coherent attempt going for it. However this is my problem with non-reductive physicalism, it conflates having an extremely complex explanation of something that could really benefit from layman’s terms (such as psychological discourse), with no detailed explanation being available via physics. Thus undermining Physicalism.
We can definitely talk all day long about super complexity and the need to explain super complex things in layman’s terms because the explanations are just so far over people’s heads that they don’t make sense. But that’s not the same thing as the claim that an explanation in all of its complexity can not be given. I need you to give me the General Theory of Relativity in layman’s terms because the full mathematical explanation is gibberish to me, but that doesn’t mean that there isn’t a complete mathematical description available for it. It does not matter to Data from Star Trek, or to a super computer how complicated the explanation might be, the question rather is can physics provide the explanation or can’t it!? Reductive Physicalism says that it can. But I don’t even know what kind of double talk non-Reductive Physicalism is even trying to get at.
A Physicalist saying that a full blown physics explanation is not sufficient to describe what’s going on with mental states, therefore we need psychological discourse, seems pretty self defeating to me. Unless they were to follow it up by sayIng “However, we could still provide that physics description for you if you wanna try to get your head around it, but good luck!” A 70 page physics description of what a Jeep did while off roading for 30 seconds may be so complex that it’s totally useless to anyone, however such a physics description can be provided. Physicalism should offer the same thing, so I don’t even understand non-Reductive Physicalism.
Both thoughts and program execution could be dealt with best by concepts such as emergence.
I have no problem with emergence, but what emerges is off the radar of a physics description. This is precisely why Data from Star Trek is constantly confused, he’s dying to understand what has emerged. If you have a perfectly cloned qualia zombie who was programmed to perfectly mimic your neighbor Dennis, yet the qualia zombie is emotionally dark inside even though it can perfectly mimic Dennis down to every micro expression & brain state, then physics can not describe for you the difference between Dennis and the emotionally dead clone. But obviously there is a difference between them.
Let’s say that brain states A, B, and C causes brain state D to emerge, and brain state D always corresponds to the thoughts/feelings of anger. This means that two things emerged. Even if I were to convert to the emergence theory that says “No, Dennis’ clone DOES experience anger if you properly arrange all of the same physical materials in exactly the same sequences.” Even then brain state D and the thought/feeling of anger are multiple emergent properties of states A, B, and C. And these emergent properties have a distinct difference about them, one I can point out to someone with a physics explanation, but one I can not. Which totally violates what the Physicalist is trying to claim, that physics is capable of describing EVERYTHING. It seems like a partially incorrect list of examples of the Reflexive Property if one were to say;
A = A
B = B
Electrical currents from X neurons to Y neurons
= Being angry