While we talk of non-duality and whether ACIM is non-dualistic, many people also make mention of duality as if knowing what duality is. But duality is not what you think it is.
We very loosly and vaguely describe duality as there being "two or more things". That these things are "separate". This seems to be easy to put into words. But the language isn't accurate enough here. Are they TOTALLY separate things?
When you look at it closer, for example, we could say there are two cars, they are separate from each other in space, and therefore there are two separate objects. But if you look even closer you'll have to admit that they in fact do share something. They both exist in the same realm. They share spacetime.
Then, ask yourself, what would total complete separateness be like? Well, it would have to be the difference between existence and total non-existence. To make something TRULY separate from something else, it could not exist in the same realm. Just as existence and non-existence are TOTALLY separate and complete opposites, and they do NOT SHARE the same realm otherwise they would share something.
So what we have are actually two concepts. One is "absolute separation" and one is "relative separation". For something to be "totally" something, it has to be absolutely that. For an object to be totally separate, it has to be ABSOLUTELY separate. But to be absolutely separate, it cannot share ANYTHING at all with the other, not even existing in the same realm. If one car existed in "existence", another car would have to be in "non-existence" in order for them to be ABSOLUTELY separate. Totally and utterly cut off from each other at all levels.
Since the two cars actually share the same realm, they cannot be absolutely separate. In fact you can easily prove that by the fact you can SEE both of them simultaneously. They can sit next to each other, they can even touch each other. So they are not absolutely separate. You can even crash the two cars and insert some pieces of one car into the other. They are not absolutely separate from each other. You can even melt one of them down and make body parts for the other one. They are not totally kept aprt.
But the cars are relatively separate. There is a degree of seeming separation. The degree also can vary from "none" to "some" or even to what might seem "mostly", but they can never reach "absolutely separate." So they are not really absolutely in a state of "duality", ever. Duality is not, therefore, really a state of absolute separation. Duality really means RELATIVE SEPARATION. Which means, at best, PARTIAL separation. And if something is only partly separate, it is not really separate at all.
This also gives rise to the idea that if they are only RELATIVELY separate, they must be PARTLY connected. They must share something. They do at least share spacetime. And at most, they could share the same materials. But this idea of relative separation indicates both that they are neither TOTALLY joined, OR totally separate. They are partly joined, and partly separate, because all illusions are contradictory. This is also beause spacetime was made as an attempt to believe that BOTH sharing and separation exist in the same place.
Science has also been proving this. Recent quantum theories suggest that an object isn't really anything in its own right, it is only something in relation to something else. Like, objects depend on other objects for their identity. Or rather, what something is, as an illusory object, is inferred or is indirect or "shared with" or implied by something else. That some of its identity is in another thing, because they share a little. And since no object is totally separate, no object has an entire absolute identity of its own. Which makes all objects symbols and not ends in themselves.
This is reflected in ACIM in terms like "at no time does the body really exist" "it is either anticipated for remembered". And "the body is not an end in itself". And "the body is a symbol". Symbols, which are what dreams are made of, ("the body is a dream"), are something which does not get its identity or nature from itself, but rather inherits it from something else that it points to or represents. Just as the body can be a symbol of eternal life, or a symbol of death/picture of crucifixion. And just as "Earth can reflect (symbolize) heaven or hell." It has no inherent absolute properties of its own, which is why we sometimes refer to it as a neutral mirror.
Also courtesy of spacetime science, there is the principle of quantum entanglement. This tells us that it does seem possible here, in this illusory world of relative separation, that one thing can be in two places at once. "Spooky action at a distance" reveals that this world is SORT OF a hologram, or at least is a devolved hologram, where the parts do not contain ALL of the whole, but do contain some of it. And so you cannot easily recognize the wholeness by focusing on the form of the parts. And the wholeness in the parts is so limited that they all appear to be unlike each other and not a hologram at all.
The idea that one particle or photon etc can seem to have entangled, ie shared, influence in total transcendence of spatial distance, tells you that the objects here are not QUITE separate. They DO share something. They ARE all connected in some underlying way. It's just that their connectedness is SO distorted and extremely de-emphasized by the forms of difference, that it seems very un-obvious and hard to recognize. This is part of the temptation of illusions. Quantum entanglement does indicate that duality is not really absolute duality, it's only a state of "relative separation". And if you look deeply enough (e.g. at quantum levels) you start to see a holographic kind of sharing that transcends spatial separation.
People go on to talk about non-duality or the seeming total absolute lack of separateness. As if non-duality is diametrically opposite to duality. In technical terms, absolute non-existence is the diametric opposite of absolute existence. But duality isn't absolute non-existence. It's only relative. ACIM confirms this here:
"The opposite of (eternal) life can only be another form of life (not totally absolute no-life). As such, it can be reconciled with what created it, because it is not (absolutely) opposite in truth. Its form may change; it may appear to be what it is not. Yet mind is mind awake or sleeping. It is **not its opposite** in anything created, nor in what it ***seems to make*** when it believes it sleeps."
This would sound totally cryptic and confusing unless you recognized that duality is not really what people think of as duality. It isn't a state of absolute separation, it's only a state of the illusion of trying to be separate, or of partial/relative separation. It's just a BELIEF IN separation, in a state of the DENIAL that everything is shared. So it is still WITHIN the confines of mind which can NEVER be separate in truth. All it can do is deny (hide, obscure, disguise) unity. And without this disguise (which is death), it is nothing.
"Without the idea of death (denial of unity) there is no world."Which means that duality is still housed within the mind as a mis-creative use of mind, a lower-order reality, and a system of thought within that same mind. Duality is NOT "actually outside of God". Outside of God is total non-existence, and it doesn't exist at all, not even as an illusion. In this world, you are NOT in non-existence. You are still in existence, pretending not to be.
The "dualistic world" is simply a mis-created devolved level of thought within the one mind, which attempts to use mind against itself or freedom against freedom or will against will, to present an illusion of relative separation, symbolizing separation and opposition. It is still something the Son of God is "making" in his mind, dreaming of, inventing, but it is an attempt to reject the sane true nature of the mind. So it results in illusions of separateness, which are not really separateness.
I like to think of this world as a kind of "last truck stop" on the way to leaving God. We never really get outside of God's envelope. But the world is the "last dying breath", as it were, in the effort to absolutely leave God and go outside of God to be "separate from Him". And physical death is just how it appears as you try to "remove all life" from something so that it can be "empty of life" and devoid of God. Trying to leave God, produces death, as a symptom of "the rejection of existence."
If you could be absolutely separate from God you would leave God entirely and enter "non-existence". This is what death of the body symbolizes, the attempt to LEAVE and actually separate from existence. As if you can go to oblivion and finally be totally without God, in absolute separation. Of course, that is impossible because non-existence doesn't exist and God is everywhere.
We never really leave God or get outside of Him, or go beyond the mind, but we do invent illusions of - lies about - symbols of - the idea of not being IN him. Of being exiled from or outside of heaven.
And this world of "duality" that we made is not so much ACTUAL duality, as it is just a state of PARTIAL duality. Of attempted separation, that fails. And of impossibilities believed to be possible while still being impossible.
So duality does not really mean what people usually think it means. It's not just about "separate things" or "a count of two or more". These are based on very loose separations that aren't really total separations. My apple and my orange are not REALLY totally separate, nor are they really part of a duality. They just appear to be separate things based on form and appearances, which are deceptive. The apple and the orange are connected together by the fabric of spacetime.
String theory and the notion that something exists as a "quantum field" which coalesces into a "concentration" of energy showing up as a particle, is just another extension of this. It's just how everything is part of a giant pool of energy, as it were, in this world, in the background, which seems to become more focused as consciousness (mind) interacts with it, producing physical matter. Ultimately everything in the world dwells "unfocused" in the quantum field which is a more shared state. This is also why subatomic particles are not actual "absolute particles", they are "probabilities".
Duality's "partialness" and relativity is also why this is possible:"Not even what the Son of God made in insanity, could be without a hidden spark of beauty, that gentleness could release."
The hidden beauty is in seeing the connectedness of things which would otherwise seem mostly separate. And thus the world, earth, can be seen as a forgiven world which symbolizes heaven, a reflection of heaven, "a sign (symbolic representation) of God's perfection" etc. The forgiven world is what you see when you look beyond the illusions of partial duality and see an underlying singular background... the one dream. The one illusion. The face of christ, seen through perception. Even in supposed separation we are not really outside of God.
"There is another Maker of the world, the simultaneous Corrector of the mad belief that ANYTHING could be established and maintained without ***some link that kept it still within the laws of God***; NOT as the law itself upholds the universe as God created it, but in some form adapted to the need the Son of God believes he has."
We ARE still within God. We ARE still within God's holographic thought system. And we ARE still always creating. And we ARE always still joined together. The physical world is just an attempt to make it SEEM as if that's not true, using the clay of creation to form appearances of the opposite of creation. But creation HAS no opposite, and even what we made or asserted in our mis-creating is still WITHIN our mind and USING its power. Even a sleeping mind is STILL a powerful mind. "The mind is always creating, it never sleeps". Even a dream of death still has a thread of connectivity running through it. This is also why death is not an end and is just pretend death.
When you redefine duality as "attempted partial separation" or "relative separation", it has to acknowledge that even duality is still INSIDE OF the dreaming mind of Sons of God. And that means you are still in heaven. "You are safe in heaven, dreaming of exile, but perfectly capable of waking to reality." This doesn't mean the dualistic world is TRUE REALITY, because its forms are an illusion of opposition to reality, but they are MADE OF mind-stuff.
"We also have observed that man can create an empty shell, but cannot create nothing at all. This emptiness provides the screen for the misuse of projection."
Spacetime is the empty shell, an attempt to create nothing, which produces an actual creation of a seeming lack of content, produces form. And then we project illusions into this emptiness or "idea of lack and limitation" (mortality) as we dream. Because even in your dreaming, you are using your mind's power TO dream, TO make illusions, and TO deceive yourself.
Never do you go outside of mind. And never do you leave God or heaven. It's just that this world cannot BE heaven because it symbolizes its absence. Even as a reflection of heaven it only symbolizes heaven. Because it's a perceptual realm and "perception is a separated state." - a state of an illusion of being separate. Illusions of separation ARE NOT absolute separation.
Only God's Kingdom is true absolute permanent reality. Your dream world is temporary and relatively partially created. And what is not absolutely created is not FULLY created at all. And so it remains just a state of temporary instanity, hallucination, wishful thinking and fiction.