So, ok, it's by definition impossible for an outsider to spot a philosophical zombie, but could a philosophical zombie introspectively look inside itself and realize that it has no qualia?
Why are we discussing qualia right now?
- If we discuss qualia because we experience it, a philosophical zombie would not. They would thus be distinguishable from conscious people. (Under this interpretation, the philosophical zombie is externally distinguishable, which contradicts its definition.)
- If we discuss qualia for some reason not related to consciousness, our concept of qualia is not grounded on actual consciousness: what we call "consciousness" is not true consciousness. (Under this interpretation, the philosophical zombie has what we call consciousness, but not "true consciousness", whatever that is.)
I find the strong form of a philosophical zombie – one that lacks consciousness experience, but is otherwise identical to a conscious person, and is theoretically indistinguishable from one from the outside – incoherent.
Being able to realise that you lack certain classes of qualia is different to actually realising it, though. Aphantasia was probably first attested in 1880, but actually noticing this difference in qualia is rare enough that pretty much nobody studied it from 1900 until 2005, when one individual with the ability to visualise mental images suddenly lost it.
Plenty of people with congenital aphantasia assume that talk of "visualising" things was mere metaphor, until they learn that actually, some people can experience seeing imagined pictures. If the philosophical zombie learned about the concept of qualia and how people talk about it, and nobody ever really thought too hard about whether the zombie was conscious, they might never realise the difference. And that's assuming the zombie is acting in good faith.
Imagine a predictive text algorithm that learns how people use the referent "I" when discussing qualia, and can faithfully reproduce its part of the conversation about qualia: the insights about how it feels to be conscious have to come from somewhere, but they don't have to come from the zombie. The predictive text algorithm's "goal" (to the extent we can anthropomorphise it) is not to answer questions truthfully, but to answer them typically. To the extent it has a concept of truth, it's "what do people truly respond to this sequence of words?", not "what true proposition is relevant to this query?". "Am I conscious?" is not a question that the predictive text algorithm would ever ask itself; to the extent that "I" has meaning to it, the pronoun refers only to a character in the dialogue.
A sufficiently-advanced predictive text algorithm, trained on enough writings about consciousness, would appear conscious regardless of whether it was actually conscious. If it were a zombie, it would never realise it; there wouldn't be anything to do the realising.
Under this weaker definition of "philosophical zombie", the space of possible zombie minds is too large for me to know how large it is; I lack the hubris to claim anything about their properties in general.
I would like to offer a different line of reasoning:
- If a p-zombie can recognize it has no qualia, then it is distinguishable from conscious beings, regardless if this act itself counts as qualia or not. So a p-zombie cannot recognize it has no qualia.
- By the same token, either a p-zombie recognizes that it has qualia (ie not absence of qualia), thus either qualia or p-zombie is incoherent. Or cannot recognize it has qualia only when qualia are missing, thus its lack of recognition means lack of qualia, thus is distinguishable. Or cannot recognize it has qualia even if they are there.
- If a p-zombie cannot recognize it has qualia even if they are there, it is conceivable it might as well have qualia. Either qualia or p-zombie is incoherent.
- If qualia are such that their presence is always recognised, then their absence produces a distinct state, at least in terms of informational content, which is conceivably distinguishable, eg by consistent questioning about information on qualia and associated behavior consistent with that. If anything can be provided as information on qualia, qualia is an incoherent concept. Else if it can provide the information, it is conceivable it has qualia.
- In any case a p-zombie as is defined is incoherent.
- ANTI-ZOMBIE ARGUMENT
- ZOOMBIE ARGUMENT
- ZIMBOE ARGUMENT
- The Unsoundness of Arguments From Conceivability
[..] the inability of our ancestors in the fourteenth century to imagine, say, genetic engineering does not show that genetic engineering is impossible, any more than their belief that they could conceive of lead being transmuted into gold by the application of the appropriate chemical process (consistently with all the actual laws of physics) showed that this is in fact logically possible.
[..] No matter how these details are fleshed out, my main point for present purposes is that the following is a necessary condition on any plausible account of ideal conceivability: one’s conceiving of X can count as ideal only if the removal of any existing epistemic distortions (of the general sort described above) would not result in X’s ceasing to be conceivable. For example, if we could come to see X as inconceivable through acquiring a new piece of knowledge, then X cannot now be for us ideally conceivable. This is not by any means an overly ambitious criterion for ideal conceivability. In particular, it does not require that some X can only be for us ideally conceivable if we are already in relevantly epistemically ideal conditions—a tall order indeed. It merely requires that if we were in relevantly epistemically ideal conditions we would continue to see X as conceivable. Indeed, this condition is simply a requirement of the fact that ideal conceivability is supposed to be a reliable a priori indicator of logical possibility: this requires minimally that its judgements should be stable in the face of the acquisition of new knowledge, or the shedding of false beliefs.
[..] The systematic problem with arguments from conceivability, then, is the following: unless we are already in relevantly epistemically ideal conditions, the justification of the modal sub- conclusion of an argument from conceivability can in principle never be completed.
[..] I shall focus on the case of zombie worlds. Chalmers’ argument, then, rests on two claims:
- “If a physically identical zombie world is logically possible, it follows that the presence of consciousness is an extra fact about our world, not guaranteed by the physical facts alone” (1996, 123).
- Physically identical zombie worlds are logically possible.
What makes Chalmers’ argument an argument from conceivability is that his defence of both of these claims rests ultimately on considerations about what is and is not conceivable. In order to establish Claim 1—that the logical or conceptual possibility of zombie worlds is sufficient to falsify materialism—Chalmers must answer philosophers who claim that materialism is content to rule out metaphysically possible zombie worlds, and is consistent with the ‘logical possibility’ of zombie worlds. In other words, Chalmers must show that the relevant modal judgements are a priori rather than a posteriori. 12 And in order to establish Claim 2, Chalmers must show that zombie worlds are in fact logically possible.
For further arguments regarding the (in-)conceivability of the p-zombie see related entry at SEP
(adapted from my other answer)
PS: Currently there is no machine intelligence algorithm able to pass the Turing test consistently. Even if this becomes possible, it will still be different from human beings, eg by being structurally different (ie being a machine). So there is no issue of a sentient machine being an exact duplicate of me or anyone else.