The National Institute of Standards and Technology (NIST) is supporting a proposal to revise the International System of Units (SI), the modern metric system, to base it on seven constants of nature rather than physical artifacts. The current SI still relies on a 130-year-old platinum-iridium cylinder to define the kilogram, which poses long-term stability issues. The proposed revision would define the kilogram in terms of the Planck constant h, an important quantum physics constant. NIST is contributing to this effort through experiments like the watt balance and determinations of the mass of one mole of silicon atoms. The Consultative Committee for Units, of which NIST is a member, submitted a proposal for a revised SI to the International Committee for Weights and Measures (CIPM) in October 2010. If approved by the CIPM and the General Conference on Weights and Measures (CGPM), a new SI could be adopted later in the decade.
Keywords: Quantum, Constants, Planck, Boltzmann, Metrology
