Local Physical Magnitudes

Non-locality, as the term suggests, is best approached via the notion of locality. As it will be seen, the notion of locality as it appears in physics has several components, but the foundational component is that of a local state in space-time. If one conceives of space-time as a four-dimensional (or eleven- or twenty-six-dimensional) manifold, one can think of covering the manifold with overlapping open neighborhoods, such that every point is contained within at least one neighborhood. One can also imagine indefinitely shrinking the size of the neighborhoods and indefinitely increasing their number. For any particular neighborhood, the intuitive notion of a neighborhood-local state is a physical state that depends only on what is inside the neighborhood. To get a more formal handle on this, a necessary condition for a neighborhood-local state is that the values of quantities for such a state put no constraints...