Contra Metaphysical Idealism

[bennyboy]

If everything is thought, what was the universe before there were homo sapiens? Or before there were any sapient beings?

You are still treating ideas as objects of physical entities. In an idealistic reality, reality itself is purely composed of ideas and concepts. Asking what thougth up all those ideas is like asking where the Big Bang came from-- it's an unapproachable question. I've already said in another thread that idealism doesn't solve all the mysteries and paradoxes of cosmogony. The main advantage is that it makes the problem of consciousness go away. Since ideas are seen as flexible, and the physical universe as inflexible (possibly deterministic), then the physical universe can possibly be seen as a subset of all experience/ideas, whereas it makes much less sense to say that the mind, which is obviously subjective, is a subset of the physical universe, which is defined as objective.

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The argument in the OP fails with the first premise.
"2) For every X, if X exists, then X is thought of. [premise 1]"

There is absolutely no justification of this. We discover things unthought of repeatedly.

Are you sure? Even in a physicalist model of the brain and mind, by the time something is experienced, it has been broken down and mentally reassembled completely. Name one thing you've ever discovered on a physical level but not on a mental level. It can't be done-- the moment of discovery is a mental experience.

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And note that Schroedinger came up with his cat as an example of the absurdity of that interpretation. He believed it was always either dead or alive, not in some overlapped state.

And things are not "both wave and particle"; that is a completely erroneous understanding of 'wave/particle duality'. The duality is that some things exhibit behaviors that are like our concepts of waves or particles. Those things so described are what they are - they are neither waves nor particles, they are never 'being both'.

Fine. What does an electron look like? Where, exactly, is it located in space? How about a photon? When a photon is behaving like a wave, or like a particle, what are its dimensions in space?