Consistent Histories and Quantum Measurements

Students of quantum theory always find it a very difficult subject. To begin with, it involves unfamiliar mathematics: partial differential equations, functional analysis, and probability theory. But the main difficulty, both for students and their teachers, is relating the mathematical structure of the theory to physical reality. What is it in the laboratory that corresponds to a wavefunction, or to an angular momentum operator? Or, to use the picturesque term introduced by John Bell, what are the “beables” (pronounced BE‐uh‐bulls) of quantum theory—that is to say, the physical referents of the mathematical terms?