It seems stupendously meaningful that pain is painful for all of us.
Drifting back to an old point, there is [currently] no known way to determine whether the colours that I see are the same as the colours you see. When you and I look at an object that I think is red, do you see the same red? While this is an interesting question to play around with, I see little significance in whether we really do see the same colours. Indeed, the answer appears to be that the consistency between our visual experience is high, though it is shaped by many factors.
But what of emotion? When tennis doubles partners win a game together, is the happiness they feel the same happiness? Perhaps the happiness I feel is the same as the pain you feel and we respond in different ways.
Yet it seems strange that we should all have the same set of emotions and could feel differently from each other for any particular emotion. Moreover, in nature we tend to find that no matter where you are, given the same building blocks and environmental factors, the same result pops out. Would not a difference in emotional feeling be a difference in nature's solution, despite a utilisation of the same building blocks?
Of course it's undeniable that no two people put in the same situation will be emotionally affected in precicely the same way. It is also the case that no two people's brains will be structured identically on at least the neuronal level. Nor will the uptake of this chemical or that neurotransmitter be the same. This diversity leads to the complexity we see in human and animal behaviour as well as some of our own experience. But this is not what I am talking about.
I believe that if two people are equally happy, they must feel exceedingly similar. In reality, our emotions are not compartmentalised; stating that "I am happy" does not mean that I am experiencing only happiness. The dominant feeling of happiness that I am experiencing and paying attention to will be fringed with other emotions. This is comparable with the way we see: while we regularly engross in a single point of visual focus, throughout this time which we maintain a mild awareness of our fuzzy surroundings. Our experience consists of a range of seemingly continuous and very much intermingled emotion.
There must be an important point hidden somewhere in all this mess of thought - an idea that may shed some light upon the nature of consciousness.
What I draw from this is that there is something in the nature of emotional events that must have fundamentally, universally associated feelings. Or that feelings emerge as the result of some other fundamental process. I believe that if, hypothetically, you instantly switched some neurons involved in one person's sadness with the neurons of another's happiness, the individuals would experience no difference. (Ignoring the numerous flaws here and considering this conceptually.) It seems to me that experience is not coded in neuronal spiking or some such higher level process, though it may be more basic. It seems to me that conscious experience has something to do with information.
This post has been rather unclear and messy-minded. I hope to improve on it! An afterthought: do you think that it is possible to have a different set of feelings from those of our own?