RE: Are there 3 worlds that are fundamentally different ?
I don't think so. You question the realness of anything that cannot be scientifically proved. I find it quite limiting and actually useless. Useless in that sense that in order to live we need to know how to live and science does not deal with that.
My approach is different. I treat evolution seriously: as the mechanism which reveals the ultimate truth. Thus anything that survived the process of evolution is real, and very old concepts like "time", "god", "sacrifice", "consciousness", "pain", "suffering", "chaos/order", "good/evil" are very old thus very real.
Applying to those concepts the requirement of scientific evidence is similar to requiring that I prove to you that e.g. numbers exist. Are numbers real? They are meta-real, they exist as an abstraction so they are more real than their actual implementation. The concept of numbers survived the human evolution so it's real.
Weird, I didn't get notified for any of these comments, had to manually come here after you told me!
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.