The following is modified from an email I recently sent to a philosopher.
The philosophy of idealism says the world is a mental experience - the world is essentially mind. This is one of the preliminary steps on the way to non duality. After recognizing the world is indeed mental, the adventurer has to then inquire into the nature of the mind - what is the mind after all? - and through meditative research comes to know that mind too is an appearance, like the shadow that appears when you stand in the sun.
The mind is the movement of consciousness (or awareness, being, Brahman, take your pick), and non duality says that consciousness alone exists. It is uncompromising in this statement. There is no wiggle room. Consciousness alone is. The corollary it adds is that all appearance, including the mental world of idealism, is "false." It is very particular in saying "false" although it is often casually translate it as "unreal." False implies that what appears to be is just that, an appearance. A realist might reply, "But I experience it! It has some reality!" The word "false reflects this relative reality, where the localized sense of "I" and the perceived "it" are movements of the mind with no independent, intrinsic substantiality.
The best example is the latest dream you had. If we had to describe your dream while being awake to its dream nature, it would be best to call it false. Calling it unreal would seem to be too much of a stretch - after all we would be experiencing it! - but on waking we would agree, perhaps, that it was only relatively real.
Monist idealism takes experience as primary and says all experience is mental. Non duality says experience is a movement of the mind.
When mind stills, reality reveals itself as pure consciousness alone - pristine, naked, infinite, untouched and untouchable by experience.
This is consciousness, in which there are no parts, no mind.
In my understanding, idealism does not differentiate mind from consciousness. Yet the two are so different that they may as well be unrelated. One is appearance, the other is reality.
There indeed is no physical explanation for anything. "Physical" is generally defined as relating to the body (as opposed to mind) or relating to that which is perceived through the senses. This is simply a categorizing of mental experience. What does the word "physical" really mean? The realist is tricked by the experience of things feeling "hard" or seeing something "outside" or "away" from him/herself. In reality, these are mental notions.
All explanations are characterizations of the mind, a subcategory of which we call "physical" without knowing the ontology of the so-called physical world. Science is a mental process of observing, hypothesizing, experimenting, and drawing conclusions. Even if we assume an external physical world, it should be clear that that the scientific method is processed in and by the minds of scientists. Science is a mental activity!
There is no independent physical reality. All appearances are mental. And all mentality is the apparent movement of consciousness.
When the mind moves, it polarizes. This is the nature of mind. This polarity is what creates mental notions of a 4D world (three dimensions of space plus the dimension of time). Three of the most fundamental mental movements are space (here v there), time (now v then), and identity (me v you or the world). These are not independently real. They come and go in consciousness.
In deep sleep, the polarity disappears. So too, in the deep meditative state which is first practiced and later becomes a new baseline, polarity disappears. In non duality, the sense of identity is not localized.
If "I" is not localized, then "you" loses meaning. All existence is then known as the infinite "I."
If the mental movement "here v there" is believed to be real, the person experiences internality and externality. He/she experiences a wall that separates him/her from the world, and along with that often comes neuroses and mental suffering, often unrecognized because it is the baseline in society. This is the basis for questions about why apparently separate individuals have common intersubjective experiences. The very question assumes separation.
If there is no separation, there is no question about intersubjective experience. Indeed, at the level of the total mind, there is no intersubjective experience. There is only mind, which differentiates into local identities and local experience. Part of that experience is a dividing wall between "you" and "me." The dividing wall does not divide the entire mind, only part of it. Hence some experience is shared and some isn't.
The mind we experience is layered. You cannot read my mind and I cannot read your mind, unless we practice. As individuals, we have notions of local identity that seem to separate our private mental experiences (thoughts, feelings, etc) from the outside world. But the mind is not only in the individual. Look all around you. Now look within you. All that you experience, including that nebulous line between outside and inside, is mind (monistic idealism). This must be the starting point for clear understanding.
It is not merely that our perceptions are not always an accurate portrayal of reality, it is that perceptions are never reality itself. Our perceptions are an infinitesimal glimpse into reality. Our eyes perceive wavelengths between 400 and 700 nanometers. Imagine how small a slice we are seeing! Multiply that limitation by our five senses. Then consider that these five senses are all we experience of the "outside" world, whereas there may be more senses available to other species that are simply unrecognizable to us. Further consider that any perception, no matter how refined and comprehensive, is still a representation or interpretation of reality. Taken together, these considerations are mind boggling.
Perception does not approach reality in the slightest.
Naive realism and scientific realism are technically different but essentially the same. They both represent a mind locked in the world of perception. The favored method of escape is to enhance perceptions through technology, which is simply a way to chase our tail longer by seeing new and exciting perceptions. Enhancing perception is useful, but cannot reveal reality. To know truth, perception has to be seen through, not enhanced. (However, I do think enhancing perception can be helpful in showing us that there is much more to the universe than what we think. But such experiences must guide us to redirect our attention otherwise we're in for more of the same.)
Neither non duality nor idealism is needed to refute naive realism and scientific realism. Only reason is needed.
Scientists have recognized the limits of perception and are now trying to research consciousness through its supposed surrogate - neural correlates of consciousness (NCC). This term is a misnomer. Neural correlates of consciousness (activities of neurons in the brain) are actually neural correlates of experience, or mind. As explained earlier, the difference between mind and consciousness is vast, though the terms are often used interchangeably in science and philosophy. Science must be precise if it is to advance into new domains of understanding.
Science does not know what consciousness is. It knows only aspects of the mind. It must recognize the difference to venture further.
Anoop Kumar, MD, MM is the author of Michelangelo's Medicine: How redefining the human body will transform health and healthcare. He is a practicing emergency physician in the Washington, DC metro area.