ON THE REDEFINITION OF THE FOUR BASE SI UNITS FUNDAMENTAL PROBLEMS IN METROLOGY

Selection of a fundamental physical constant for the purpose of redefinition of the updated SI base measurement unit according to the principle of concordance of dimensions of the constant and of the unit of measurement, when they either coincide or differ by a factor having the dimension of time, is proposed. A quantitative criterion for reconciling the new prototypes of the kilogram with its international prototype and a quantitative limitation of their instability are proposed. The possibility of preserving a relation between the definitions of the mole and the kilogram in the updated SI is considered. It is proposed that the kilogram and mole be redefined using a fixed value of the Avogadro constant, the kelvin, and the ampere, after, that is, the measurement accuracy of the Boltzmann constant has been improved and after closure of In Resolution 1, On a possible future review of the System of Units, adopted at the 24th General Conference on Weights and Measures, it was proposed that the International Conference on Weights and Measures contin- ue research to improve the formulations of the definitions of the base SI units in terms of the fundamental constants and ren- der the descriptions as simple as possible for users' understanding, following the principles of scientific rigor and clarity of presentation (1). The objective of the present article is to discuss certain modifications of the new formulations of the four SI base units (kilogram, mole, ampere, and kelvin) and procedures for redefining these units by means of fixed values of the fundamental physical constants, a step that will promote the solution of a number of problems mentioned at the 24th General Conference on Weights and Measures. It is well known that a redefinition of the four units on the basis of fixed values of the fundamental physical con- stants within the framework of a new SI rests on the principle of fixation of the exact value of the corresponding constant, which was used in the definition of the meter in 1983. It was proposed that the exact values of the four constants h, e, k, and N A be fixed with zero uncertainty and the kilogram, ampere, kelvin, and mole then redefined by means of these values (1-7). The use of exact values of the fundamental physical constants is of great importance for metrology (8-12), and these sug- gestions received support on the part of metrological organizations and at meetings and conferences (1, 3, 5, 6). In the present article, we will focus on certain drawbacks in the proposals (7) and present a modified approach to the selection of the con- stants in order to perform a procedure of redefinition of the four units and ultimately refine the formulations of the definitions and select the fundamental physical constants.