The holy problem of qualia may actually be close to the question at hand here.
What do you mean when you ask yourself: "Does my neighbor have qualia?"
Do you mean: "Does my neighbor have the same experiences?" No. You know for sure that the answer is "No." Your brains and minds are not connected. What's going on in your neighbor's head will never be your experiences. It doesn't matter whether it's (ontologically) magical blue fire or complex neural squiggles. Your experiences and your neighbor's brain processes are different things anyway.
What do you mean when you ask yourself: "Are my neighbor's brain processes similar to my experiences?" What degree of similarity or resemblance do you mean?
Some people think that this is purely a value question. It is an arbitrary decision by a piece of the Universe about which other pieces of the Universe it will empathize with.
Yes, some people try to solve this question through Advaita. One can try to view the Universe as a single mind suffering from dissociative disorder. I know that if my brain and my neighbor's brain are connected in a certain way, then I will feel his suffering as my suffering. But I also know that if my brain and an atomic bomb are connected in a certain way, then I will feel the thermonuclear explosion as an orgasm. Should I empathize with atomic bombs?
We can try to look at the problem a little differently. The main difference between my sensation of pain and my neighbor's sensation of pain is the individual neural encoding. But I do not sense the neural encoding of my sensations. Or I do not sense that I sense it. If you make a million copies of me, whose memories and sensations are translated into different neural encodings (while maintaining informational identity), then none of them will be able to say with certainty what neural encoding it currently has. Perhaps, when analyzing the question "what is suffering", we should discard the aspect of individual neural encoding. That is, suffering is any material process that would become suffering for me if it were translated into my neural encoding within the framework of certain translation technologies.
But the devil is in the details. Again, "certain translation technologies" could make me perceive the explosion of an atomic bomb as an orgasm. On the other hand, an atomic bomb is something that I could not be, even hypothetically (unlike the thought experiment with a million copies). But, if you look from a third side, then I can’t be my neighbor either (we have different memories).
This is a very difficult and subtle question indeed. I do not want to appear to be an advocate of egoism and loneliness (I have personal reasons not to be). But this, in my opinion, is an aspect of the question that cannot be ignored.
For a long time, I wanted to ask something. I was just thinking about it again when I saw that Alicorn has a post on a similar topic. So I decided to go ahead.
The question is: what is the difference between morally neutral stimulus responces and agony? What features must an animal, machine, program, alien, human fetus, molecule, or anime character have before you will say that if their utility meter is low, it needs to be raised. For example, if you wanted to know if lobsters suffer when they're cooked alive, what exactly are you asking?
On reflection, I'm actually asking two questions: what is a morally significant agent (MSA; is there an established term for this?) whose goals you would want to further; and having determined that, under what conditions would you consider it to be suffering, so that you would?
I think that an MSA would not be defined by one feature. So try to list several features, possibly assigning relative weights to each.
IIRC, I read a study that tried to determine if fish suffer by injecting them with toxins and observing whether their reactions are planned or entirely instinctive. (They found that there's a bit of planning among bony fish, but none among the cartilaginous.) I don't know why they had to actually hurt the fish, especially in a way that didn't leave much room for planning, if all they wanted to know was if the fish can plan. But that was their definition. You might also name introspection, remembering the pain after it's over...
This is the ultimate subjective question, so the only wrong answer is one that is never given. Speak, or be wrong. I will downvote any post you don't make.
BTW, I think the most important defining feature of an MSA is ability to kick people's asses. Very humanizing.