The article discusses the proposal to redefine the kilogram, the only base unit of the International System of Units (SI) still defined by a physical artifact, in favor of a definition based on a natural phenomenon. The authors argue that the benefits of using unchanging natural phenomena to define the kilogram outweigh any drawbacks of slightly greater uncertainty in mass measurements.
The proposed redefinition would improve the precision of certain electrical measurements 50-fold and enable more precise calculations in studying the fundamental quantum properties of atoms and other basic particles. The authors suggest retaining the kilogram artifact as the working reference for highly precise comparisons to individual countries’ national kilogram standards.
Two methods are leading the effort to redefine the kilogram: the watt balance experiment, which measures a kilogram against the amount of magnetic force required to balance a 1-kilogram mass against the pull of Earth’s gravity, and the X-ray crystal density method, which involves counting the number of atoms of a specific atomic mass that equal the mass of 1 kilogram.
The authors stress that efforts should continue to reduce the measurement uncertainty of both methods, which are currently 10 to 100 times less precise than the measurement uncertainty produced when comparing the kilogram artifact to national standards. When uncertainties of these experiments reach a sufficiently low level, the cylinder artifact would no longer be needed.
Keywords: Planck, constant, precision, uncertainty, kilogram, mass, definition, atomic, measurement, metrology
