To a conscious agent within a mathematical system which models rocks and trees and people and the Moon, it looks very much as though rocks and trees and people and the Moon exist; physics appears to be real. But that appearance is in no way contingent upon anything we could reasonably define as the 'existence' of rocks and trees and people and the Moon.

Is that gleanable, or am I still talking gibberish? (I never rule out the latter, particularly on the subject of philosophy.)