Fundamentals of Measurement: The Revised SI Compared to Natural Systems of Units

Abstract

In a useful introduction to “natural units” [1], the author contrasted natural units to the SI as it existed at the time of writing (2016). The SI was characterized in [1] as a system that “relies heavily on precision measurements of standard prototypes, objects or systems that define a physical unit.” In particular, the SI indeed relied on one standard prototype, called the International Prototype of the Kilogram. The mass of this unique object defined 1 kg. By contrast, “natural units,” as the name implies, are completely defined in terms of selected constants used to describe the natural world. Different systems of natural units are based on different selections of these constants.