I was reading about qualia and how there's apparently the problem of qualia because a unique experience is constrained to one subject (?). But I don't see how this is meaningful in any way since communication between subjects is possible. Plus, we can imagine/dream a new experience by constructing it from past experiences. Seems like the "problem of qualia" belongs in the same category as solipsism, nihilism, absolute skepticism, etc. Why should I entertain such a concept? Thanks!
We can communicate although our experiences are personal because we share a universe, but our experience of perceiving this universe are personal and non shareable.
If I point to a red spot (a spot I personally perceive as red) and say "this is red" to a toddler, he will learn that what he is perceiving is to be named "red". The toddler can then proceed to ask me for "red shoes", knowing that we agree on what is red, but It does not mean we have the same experience of redness.
Although we perceive the same light frequency, the neurons that get activated in each of our brains are not the same. The way we perceive a same stimulus is not the same. IRM and other advanced imagery give us good reason to think it is very similar, but the fact is we don't have the same neurons, ordered in exactly the same manner, and thus what happens in each of our brain is personal, and something we can't share with each other.
As a materialist, I fail to see how qualia is a hint for dualism, but I find the concept of distinguishing between the stimulus, the name we give it through language and it's mapping in each individual's brain, to be, at least, thought provoking.
A thought or perception is analogous to a two-sided coin. One side is the objective brain signal and the meaning encoded by it. The other is the subjective, conscious experience of that meaning. For example if you see a red light then a particular signal pattern will arise in the region of your brain which processes consciousness. Accompanying that signal pattern is the subjective sensation of redness.
The problem is that science has no way to either predict or describe that quality of redness which you consciously experience. There is no objective criterion by which that quality can be communicated to another person. How do the perceptions of a fully sighted person compare to those of a color-blind person? Communicating things like "red is different from other colors" or "red and green look the same to me" works at the physical level but we have no idea what qualia are associated with those meanings. Worse, how do you and I know that our experiential perceptions of red and blue are not swapped over? We can check out the brain signals and deduce their meaning, but we cannot check out another consciousness's experiences to see how they are different or if they are swapped over.
This elusive subjective quality of "redness" is called a quale (pronounced "kwah-ley"). A more complex experience comprises many such qualia (plural of quale).
One cannot deny that qualia exist, as one's own consciousness comprises nothing more nor less than an ongoing stream of them.
But relating them to their objective brain events in any meaningful scientific way appears to be impossible. In the theory of mind and consciousness the nature of this relationship is known simply as "the hard problem".
Philosophers disagree profoundly as to whether one or the other side of the coin might be primary. Some, such as Dennett, regard the material world as primary and qualia to be a trivial distraction. Idealists believe quite the reverse, seeing objective reality as a delusion created by an entirely metaphysical or experiential reality. A third school, dualism, treats the material and the experiential as independent realms. And of course many variations and intermediate positions arise from these three approaches.
If you base your concept of "meaningful" on material scientific grounds, as you apparently do, then you paint yourself into the first of those schools. But that is your choice, it cannot be justified on its own terms any more than the verification principle can be - indeed, it is just the verification principle applied to consciousness.
A final note. The "problem of qualia" is quite different in kind from solipsism, nihilism or absolute skepticism. Those last are all negative approaches in that they deny or doubt the existence of something. Qualia affirm the existence of something.