It strikes me as odd to start from the position "we declare this thing to undeniably exist" and then spend generations trying to spit out even one sentence describing what evidence or explanation for its existence might even plausibly look like.
IMHO it's the old darkness/duality problem all over again — postulating some "essence" (e.g. the spiritual/religious Soul) and basing theory on a mere intuition, instead of invoking a "placeholder" (like "dark matter" isn't necessarily matter but literally "something that behaves as such" whatever it actually is, or like "dark energy" isn't necessarily a fifth interaction but certainly behaves as such or as anti-gravity of sorts; wherein "dark" means "unknown and hidden from direct observation, merely inferred"). Hence my call to not infer the very measurement thereof if we are to call an explanatory hypothesis.
Should we start by stating that "qualia" or "consciousness" or whatever is a placeholder name for "whatever dark (unknown, black-box) mechanism explains the observable phenomenon named as such", then we might have a chance at actually forming a coherent theory thereof. IMHO.
Perhaps, although in the case of qualia I’m not sure what the phenomenon is that we need a placeholder explanation for. For dark matter we’ve got certain observations of galaxies. For qualia we’ve got, what? A lot of people who feel very strongly that they are unable to deny the existence of something that they cannot describe beyond that claim of undeniable existence? If that’s how astrophysicists explained dark matter I’d be inclined to think that maybe it just doesn’t exist.
Edit: thanks to autocomplete we were briefly embroiled in an argument about the existence of quails.
Seems to me that the bafflement I'm experiencing at people doubting human sensory experience is the real bit, and the neural network that might be able to perfectly replicate my bafflement in silicon is the purely hypothetical construct.
In theory, if we had high-throughput brain-brain interfaces that could be connected between your thalamus and someone else's, then yes, they could experience the same sensations as you. Of course, besides the challenge of having high-throughput hardware embedded in your brain without killing you, there's also the challenge that brains don't have exact correspondences between every neuron for different people, so any such mapping would be quite complex.
But there is an actual example of a pair of conjoined twins who share the same thalamus and can experience the same sensations as one another: https://en.m.wikipedia.org/wiki/Krista_and_Tatiana_Hogan
> it was confirmed that they share a thalamus which connects their brainstems. Through this shared brain tissue structure and the interconnected neurons, one brain receives signals from the other brain and vice versa. This documentary also reported on experiments that were carried out that confirmed that visual cortex signals based on what one girl saw, were received by both girls' brains. So in effect, one twin could see what the other twin was seeing, making them unique even among craniopagus twins.
Also...
> I'm also certain my sensory experiences are not identical to attempts to quantify them or describe them in language or interpretive dance (philosophers struggling to define and articulate things even at high levels of abstraction is weak evidence in favour of qualia, since the defining aspect of qualia is its the portion of human brain state that can't be communicated).
Language is a very low-fidelity way to express information; we can use abstractions to make up for quite a bit, but it doesn't make sense to think that we're accurately transmitting what's going on in every molecule of our bodies when we say what something feels like to us. And even if we could send an accurate account of all those details, who would have the time to parse through and make sense of it all? And that would be a momentary expression of who we are; it'd be inaccurate in the next moment.
That's sort of the point though, it's incredibly low fidelity (so low fidelity that computers we're absolutely sure don't have sensory experiences can appropriately and plausibly describe them) yet just about high fidelity enough for me to be sure that people experiencing synesthesia must be having different experiences than me, and there's no particular reason to believe we are or ever will be on a path to me being able to experience their experience in any meaningful way. Even in the twins' case where the transmission mechanism is literally the same substrate connected to the same physical organs that have developed simultaneously, the reports of them having different personalities and preferences suggests that they have different sensory experiences from [partially] shared inputs.
The thorny question then becomes whether sensory experiences are important to independent goal formation and other stuff often considered part of general intelligence. I don't think we know enough to answer that question, but we certainly don't know enough to dismiss it.