On the philosophical significance of the reform of the International System of Units (SI): A double-adjustment account of scientific enquiry

The philosophical significance attached to the construction of systems of units has traditionally been confined to the notion of convention, while their adoption was considered to be the exclusive province of the history and sociology of science. Against this tradition, a close articulation between history, philosophy, and sociology of science is needed in order to analyse the recent reform of the International system of units (SI). In the new SI, units are redefined on the basis of certain fundamental constants of nature, established by physical theories, whose values are fixed without uncertainty. The purpose of this article is to show that the redefinition of SI units, far from being a convention, involves a holistic reconstruction of our concepts of quantities from accepted theoretical laws. Fixing the values of the defining constants stabilizes these laws within the framework of physics through a twofold adjustment procedure that ensures both a semantic coordination between theory and world and an intersubjective coordination between human agents required by social activities. This double adjustment results in closely entwining the pursuit of truth as correspondence and truth as coherence which turn out to be complementary, thus highlighting the anthropological underpinnings of scientific realism.

SI-2019 and prospects for improving the accuracy of electrical measurements

Increasing requirements for the accuracy of measurements have led to the need to revise the existing International System of Units (SI). The important element of the SI-2019 reform is “the establishment of the SI base units through seven defining constants, the numerical values of which are fixed”. The approach to the establishment of the measurement units has fundamentally changed. If earlier a definition was given of how the unit is realized, now only the exact numerical values of the fundamental constants are fixed, and their values are expressed in the corresponding SI units. Measurement units are determined on the basis of known physical laws, which include certain fundamental constants. The article analyzes the changes in SI-2019 related to electrical measurements, and also discusses the prospects for the development of accurate electrical measurements.

Explaining to different audiences the new definition and experimental realizations of the kilogram

Different options were discussed before reaching the final agreement on the new definitions of the SI units, effective from 20 May 2019, especially with regard to the kilogram, now defined in terms of the numerical value of the Planck constant (h). Replacing the artefact definition of the kilogram with a new one based on the mass of a particle, or the atomic mass constant (mu), would have been preferable for ease of understanding, among other reasons. In this paper we discuss some limitations of teaching to different audiences what a kilogram is in the redefined International System of Units (SI), including realizations of the new definition.