We seem to have indirect evidence: no actual separation, division was ever found in the universe, not even between the 'contents of the mind' and the 'mere stuff out there'. And we seem to have direct evidence in quantum nonseparability that even ignores spacetime, and is arguably universal, we just can't always track it.
(Now of course this could still just be circular, partial, illusory etc. etc. like everything else, but it's the best we can work with right now as I see it.)
Of course, it's circular, but not in a bad way. In an inevitable way. When it comes to this level of inquiry, you're going to find the biggest problem to be trying to deal with, on the one hand, a language/logic system that is always self referential, as explanations defer one to, well, other explanations. That is part of the post modern thesis. There is no way out and you find your words and paragraphs and their ideas' final justification defers
to just more of the same and thought never touches the ground. This is the problem. A quantum physicist does not go here since it is not her field, but philosophy will ask about the language one deploys to do the explaining, for the validity of language construction is presupposed by whatever it is being said. Language IS difference, that is, one word differing from another is at the very foundation making meaning at all. This is Derrida: language is always deferential. This is why Kant is so important, for Kant insisted that, in a wholly different manner, that we are stuck in this knowledge-world and there is no way out, for to even think at all puts one squarely in matrix one is trying to find a way out of in the effort to get at the elusive "truth" of things.
But before Derrida, there was the existentiaalists, the phenomenologists. They are "the best we can do" by my thinking, for their project gets to the underpinnings of thought itself. No one has the patience for this, though. Science is easier because it is familiar, having taken courses all one's life, in general science, mpre specialized in college ( I took courses in astronomy, geology, physics. Much more popular than continental philosophy. Indeed, required!) Everybody knows Newton and Einstein, but who has even heard of Husserl? Yet his thinking is deeply important.
Well they seem to be arguing among themselves as well, about what it is that's actually illusory, and how to handle the situtation etc. Eastern philosophies seem to be a huge muddy mess of many similar and not-so-similar views, centered around the same theme, with all sorts of mistakes, delusions, traps of their own. And they still tend to use 2500 year old psychology, it's pretty outdated.
And yet, they are right! I think Eastern philosophy is saying one thing in the midst of all errors, contradictions, and the rest. Liberation is the point! Not discursive "truth" (notwithstanding jnana yoga) but revelatory truth. And this requires putting down a great deal of presuppositions that implicitly rule one's thinking. Out the window goes empirical science for we are not trying to solve a particular problem and there are no entities before our eyes that need examining. It is a withdrawal from all things into the "Nothingness" (no thing. See, if you like, Michel Henry, the fairly contemporary French existentialist) of the eternal present (Kierkegaard. See his Concept of Anxiety). Existential thought goes on and on and often thematically matches up with Eastern thinking. It is our (the West) jnana yoga.
Took me a while to see clearly as well, and the form of nondualism I subscribe to may not even be that widespread, but I think it's "the" nondualism. Now of course the human ego is very much real in the sense that it's some kind of psychological structure in the human head, made of thoughts, emotions etc. What is illusory is the.. umm there is no good way to say it.. it's the illusion of the volitional, individual self-entity that "does" things, "has" things, and most importantly, "is or has consciousness somehow".
At root, I hold, it is the illusion of knowing implicit in my waking up in the morning and knowing everything that confronts me in the world is familiar, known, clear, so I can say "pass the salt' and "I hope the bus is on time." we live in an "apophantic world" to use Heidegger's language, filled with assertion, unquestioned. We see, when we read philosophy, and step back from things, that this is merely interpretative world. Now our declarations of what things are loses its grip (philosophy should
make one a little crazy) and we approach our authentic selves. So much more to say on this. So interesting for one who interested in getting at the truth of thingis.
The entirety of mainstream Western philosophy and culture is based on this illusion. Humans are self-aware creatures that believe that consiousness, being in the most fundamental sense is "theirs". But the truth is that, in the most fundamental sense, the self-aware human being is happening in consciousness (is part of and one and the same with consciousness), and this consciousness is existence itself, the world, reality. I think Watts summed it up like this: "do you define yourself as a victim of the world, or as the world"?
I used to read Watts, and I still think he is one who opens doors (of perception? Aldous Huxley's book on his experiences with mescaline are...quite interesting). Of course, to confirm that our conscious experiences are united as one beneath all we do and think is the hard thing to do. One has to become a kind of mystic and withdraw from t he everyday world and bring about a profound distance between self and everydayness. Kierkegaard called this the Knight of Faith, though he details are not structured as the the eastern mystics would have it. But at the end of the day, his thought resolves in simplicity, as in that of the Prajna Paramita: there is no wisdom, and there is no attainment whatsoever. This is K's eternal present: a singularity defeats the all struggles and differences are laid down. This would be heaven, Christian nirvana.
And here I say that we should of course not choose either this or that identification, but both at the same time. Not only is that much healthier in pretty much every way, but technically it's the most accurate view as well. So instead of crazies who try to dissolve themselves into nothingness, or crazies who start to identify themselves with a falsely reified Brahman-the-big-I, one should simply retain the original human identification somewhat, while also knowing what's "really" going on. This is my solution to the awakening issue, I've found that nondualism is actually very much compatible with individualism. (And with multiverse hypotheses and with circularity of dimension, the other two starting assumptions of what I consider to be deep ontology.)
Right. Unless you are ready to climb a Himalayan mountain and sit for the rest of your life, you are in the world. Hindu yogas allow for this. One can "yoke" oneself to the inner depths through jnana (philosophy) yoga, bahkti (devotion) yoga, dyana (meditation) yoga. The way I see it, it is a matter of the way you experience the world, and Heidegger is a very good step to understanding this. Once one decides she is going to be serious about this, measures are taken to undo the the habits of thought and experience that keep the world an ordinary place. We make this world oridinary; it is not ordinary in itself. It has to be unmade, and this is not a an accumulation of knowledge, but a destruction of knowledge, and language becomes a tool for disillusionment. This is philosophy's true purpose: it is the use of language--the question is the piety of thought, Heidegger said
-- to come to understand our higher self.
So nondualism being compatible with individualism works less and less as one gets more one gets closer to a, well, state of enlightenment. I know quite clearly now that the greater one's understanding is, the more attachments to this world fall away. It is not that one no longer knows as others do, but that one no longer cares.