Plenary talk I: The possible future revision of the International System of Units, the SI

The International Bureau of Weights and Measures (BIPM) and National Metrology Institutes (NMIs) have spent many years advancing and improving the International System of Units (SI) by extending the frontiers of metrology to allow a definition of the SI base units in terms of invariants of nature — the fundamental physical constants h, e, k and N A for the definition of the kilogram, ampere, kelvin and mole, respectively. The numerical values of the fundamental constants h, e, k and N A and their associated uncertainties will be established by CODATA using a sophisticated method to minimize the uncertainty of these values while ensuring consistency among the recommended values for all physical constants. If the results of experiments are satisfactory and the needs of users are met, formal proposals for changes in the definitions of the kilogram, ampere, kelvin and mole can be presented to a future General Conference on Weights and Measures (CGPM). The lecture will present the possible future revision of the SI, the current status of determination of the Planck, Avogadro and Boltzmann constants, the criteria for acceptance of the new definitions and the consequences for users when the ‘New SI’ is adopted at a future meeting of the CGPM.