RE: Are there 3 worlds that are fundamentally different ?
Weird, I didn't get notified for any of these comments, had to manually come here after you told me!
Yes, we have pain in plants.
We don't know. We just can't know.
That's the whole point of this, that the subjective world is inherently "hidden" to us for analysis , all we can do is monitor the brain (or the equivalent of a central nervous system for any organism) , analyse electro chemical signalling patterns and compare them to ourselves, or other beings ( for ex : rats) that we have studied closely.. that's the closest we can get to learning what the organism is "feeling"
Since plants lack a CNS, I seriously doubt their degree of consciousness would be anywhere close to ours, or other animals, which is is required to feel complicated sensations such as 'pain'..
However, if you adopt a panpsychist view, they are also conscious, and also capable of pain and pleasure, but it is very minimal, almost insignificant
And for me that's the trap of reducing everything to scientific examination: "if something cannot be objectively proved then it does not exist." I find it similar to children covering their eyes and saying that the world disappears because they cannot see it.
I agree that human consciousness might be much more than other creatures have. Yet still denying its realness is quite an arrogant act, as it assumes that via technology we have gained wisdom that exceeds very old human stories, our very foundation.