Linking the International System of Units to Fundamental Constants
The current International System of Units, SI, established in 1960 by the General Conference on Weights and Measures (CGPM) of the Metre Convention rests on the definition of seven “base units”: the metre, the kilogram, the second, the ampere, the kelvin, the mole and the candela. It serves the requirements of industry, science and society, underpins global trade and has been adopted by 97 Member and Associated States of the Metre Convention representing 97.6 % of the world’s economic power.
Innovative technologies and ever-increasing demands from industry and science are challenging the current SI. The kilogram in particular is causing concern. Moreover, the ampere, based on the 1960 definition, cannot be realized with an accuracy required by modern technology.
It is thus envisioned that the 25th CGPM redefines the SI by 2018. In the future, as outlined by Max-Planck in 1900, it will be based on fixing the numerical values of “defining constants”: the velocity of light, the charge of an electron, the Boltzmann, Avogadro and the Planck constants, the Cs hyperfine clock transition and the luminous efficacy.
This talk motivates this endeavor, illustrates the rationale behind it, introduces the new definitions and reviews their requirements. The benefits and the wide-reaching impact of this fundamental revision are presented.