Why have international metrology Heads called the New SI “fundamentally better” and could it be even better?

Abstract

In November 2018, the 26th General Conference on Weights and Measures (CGPM) adopted the changes to the In­ternational System of Units (SI), which got the conventional name “the New SI”. These changes came into force on May 20, 2019, on World Metrology Day. International metrology Heads have called it “fundamentally better”. This article is devoted to discussing such an assessment.The article shows that the whole history of metrology development is the search for optimal physical quantities and units of measurement, as well as such stable phenomena and objects of nature that could be the basis for the reproduction of these units and creation of the measurement standards.It took almost 150 years of searching and taking certain steps before the ideas of scientists were put into practice in the New SI — quantum SI. The base of this system is fundamental physical constants (FPCs) — standards of nature, micro objects have become the carriers of the sizes of units, and methods of their connection with the macrocosm — quantum phenomena and effects.The article shows that in all measurement fields where quantum methods and definitions of units were implemented through FPCs, there was a significant — by 2–3 orders of magnitude — increase in the accuracy and reliability of the realization of units.The 26th CGPM made the final decision on the new definitions of the base units. The article contains an excerpt from Resolution 1 of the 26th CGPM 2018, as well as its Annexes.An analysis of new definitions of the base units is given. It is shown that the new definitions of second, metre and candela are relevant to their definitions in the previous version of SI and differ only in wording. The definition of kilogram is fundamentally new and is based on the fixed value of Planck’s constant. Significantly new definition is also obtained by the unit of electric current. This means the recognition of quantum methods in electrical measurements, which have in practice confirmed their outstanding metrological capabilities. Definition of kelvin through the Boltzmann constant, experts believe, will contribute to the development of primary thermometry and thermodynamics as a whole.The article also highlights the fundamental advantages of the New SI and outlines the prospective tasks of metrology.