In Praise of Exact Quantization

摘要

In science, great value is placed on quantities that are exact. In physics, it is crucial for our understanding of the world around us to know that the values of fundamental physical constants, such as the mass and charge of an electron (or any other elementary particle), remain precisely the same no matter the circumstance. In solid-state physics, where we deal with complicated systems of many particles, such comforting exactness is hard to come by. A piece of iron will have electrical resistance that can vary greatly with temperature, impurity content, and other factors; the same is true of most of its other measurable properties.