[Physics] tells us a great many facts about the mathematically describable structure of physical reality, facts that it expresses with numbers and equations . . . but it doesn’t tell us anything at all about the intrinsic nature of the stuff that fleshes out this structure. Physics is silent—perfectly and forever silent—on this question. . . . What is the fundamental stuff of physical reality, the stuff that is structured in the way physics reveals? The answer, again, is that we don’t know—except insofar as this stuff takes the form of conscious experience.2
