However, the fact that you cannot imagine the unimaginable is a serious issue for physicalists.
That's just a truism, how is it a problem? Are you saying reality is restricted to what you can imagine? I don't see how you could prove that.
So to are discoveries suggesting that a single quark occupies various spaces simultaneously. An idealist can IMAGINE this as a mental entity but a phisicalist cannot replicate it.
A wave occupies various spaces simultaneously. It's not that hard to grasp, and it's laughable to say that physicalists cannot "replicate" a fact of physics. You can imagine anything as a mental entity, that doesn't explain anything that physics didn't already tell you.
An individual not being able to see something, with or without glasses, doesn't cause it not to exist.
And an individual not being able to experience something doesn't cause it not to exist either. That's the analogy.
It is the observation by A mind that causes it to persist (as the idealist would say), not that EVERY mind must observe it.
I didn't say all glasses have to observe it, just A pair of glasses. The glasses of God, if you will.
Again, you have skipped over the basis of his contention: can you imagine the unimagined?
By definition, no. So what? That's not what you initially stated. You stated that you can't imagine something independent of mind. I can, a rock independent of mind. The rock can simply exist in its own universe without a mind. What's conceptually wrong with this? Ah that you need a mind to imagine this. But that doesn't change anything about the concept, anymore than needing glasses to see changes the thing you're looking at.
Nothing he claims undercuts discoveries in science.
Of course not, it just takes whatever facts science discovers without mind having anything to do with it and adding mind to it
In fact I have spoken to physicists who have confirmed behaviors in light that are somehow dependent on observation
Yes, but "observation" in physics is an interaction in which information is generated, such as a photographic plate that light has reacted with. It has nothing to do with a mind or observer in the colloquial sense.
There is a reason people are still spilling ink on this argument on both sides of this argument.
There are a lot of silly beliefs that have persisted for a long time.