The thought system of the ego has directly produced this physical universe.
The thought system of God has directly produced heaven.
"Heaven remains your one alternative to this strange world you made and all its ways; its shifting patterns and uncertain goals, its painful pleasures and its tragic joys. God made no contradictions. What denies its own existence and attacks itself is not of Him. He did not make two minds, with Heaven as the glad effect of one, and earth the other’s sorry outcome which is Heaven’s opposite in every way."
It's not just that Heaven is "another place" that you can think about in the same way you think about Earth or this universe. Heaven THINKS DIFFERENTLY from how this world thinks, it reasons differently, it draws conclusions differently, and its logic does not operate like the ego's logic.
This world represents and is part of or inside of, the ego mind. Anything this side of the separation from God IS the ego thought system, including this universe. The ego mind's THINKING has produced this universe and all forms of matter reflect the idea of EXCLUSION.
Heaven represents and is part of or inside of, God's mind. Anything THAT side of the separation from God is the Holy Spirit's thought system, including Heaven. Heaven proceeds according to entirely different THINKING and its nature, it structure, is nothing like the ego predicts.
The two thought systems are so extremely opposite to each other, as to be nothing alike. The two "worlds" are unalike in EVERY way, and Earth being totally unlike God's nature cannot possibly have been created BY him because it is not LIKE Him at all.
The problem arises when, unfortunately, we USE the ego's thought system to attempt to look at or understand the nature of God's thought system. Extraordinary misunderstandings arise from this, because the ego's way of thinking and reasoning fundamentally *requires* seeing things in a certain way. When looking at something unlike itself, it literally cannot see it correctly without major distortions.
This is why we have to be extremely careful about the conclusions we come to about Heaven, God, Sonship, Creation etc, because in just about every case, we are USING the ego to think about it. And this has unfortunately led to a huge list of false conclusions about the nature of Heaven.
We may not realize it, but we actually THINK WITH the ego, and all of our thought processes follow ego laws and proceed according to ego rules. The way that we reason things out, the way that we "make sense" of anything, it all stays INSIDE OF the ego's thought system. When we try to use the ego to make sense of heaven, therefore, we don't actually LEAVE the ego's thought system to go TO heaven to THINK LIKE GOD, instead we look upon it from afar and make false judgements about it.
Jesus says that we need to learn to THINK LIKE GOD, and that means learning a whole different way of reasoning and thinking and concluding. A whole different way of "making sense", if we are to have any hope of comprehending WHY God acts a certain way or WHY it's possible for Him to have created individuals with free will. Or WHY He could not possibly have created this physical universe. Or HOW the nature of this world is fundamentally IMPRISONING right down to the atom.
We literally are living INSIDE the tiny mad idea, which is an idea of "separation thought" and all of our thinking follows exclusive, separating rules. These rules split things apart and make them different and pit them against each other, because it is a murderous thought system. The result of using the ego's thinking processes to evaluate God's creation is that it results in MURDER of God's creation. And yet the ego will evaluate that it has merely "made sense". When the ego makes sense of something, it makes NONSENSE.
While the Course largely focuses on USING the ego's thought system and its way of thinking, to lead you OUT of its way of thinking, this is only because it's how you DO think for the most part and so He is trying to speak our "language" and to use how WE think and reason to help us to make conclusions AGAINST the ego. But the truth remains that the way the ego thinks is fundamentally false and excluding and separating, so at some point we have to move past this to learn to think like God.
When you think like God, which is holographic INCLUSIVE logic, it becomes clear that the conclusions the ego came to about God's Creation are simply false.