The potential to enhance the information complexity of another agent. Where the degree of this potential and the degree of the complexity provided indicates the degree of moral significance.
Which reduces the problem to the somewhat less difficult one of estimating complexity and so estimating potential complexity influences among agents. By this, I means something more nuanced than algorithmic or Kolmogorov complexity. We need something that takes into account fun theory and how both simple systems and random noise are innately less complex than systems with non-trivial structure and dynamics or to put it another way, systems that interest and enrich.
Also note, don't make the error of equating the presence of complexity for the potential to enhance complexity in other agents.
As for suffering, in this context, you can define suffering as the inverse of complexity enhancement, namely the sapping of the innate complexity of the agent.
Can you explain why "the inverse of complexity enhancement" would be a good definition of "suffering" that would share the other features we mean by the word?
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.