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At least, we THINK it does, although we can't be certain, since we can't perceive anything outside of our perception. But the math seems to work out.

I find it hard to believe though that the world does not exist outside my sorry ass ...

The world exists outside of individual perception.

I call "assumption" on this statement.

I have to agree with @davidbrogan, and would like to add:

There are two types, or qualities of truth, as I see it:

1.) there's a relative "truth" that requires dividing out a subject from an objective world, or accepting that there exists subjectivity, as distinct from objectivity (an assumption as a basis point to start speaking of "truth"). Here, for instance, we can both agree that the sky is blue.

2.) there's an absolute "Truth" that requires dropping all sensory information, because either or both (the senses and the information that they perceive) can, themselves, be faulty/ illusory (think about how many things you can prove to be true during a coma-dream that lasts years - what have you really proven? It's a dream. It's not reality. They were only proofs relative to that dreamworld.). Here, I can see a "me" and a "you" and an apparent sky that's separate from these two "subjects" and, to my sight, it appears to be blue, but I can't be 100% certain that any of it has a solid reality. It could all just be a dream, or something else that I can't fathom.