Event Details

Revision of the International System of Units

Abstract: The International System of Units (SI) is the only globally agreed practical system of measurement units. Stemming from the Metre Convention of 1875, which established a permanent organisational structure for member governments to act in common accord on all matters relating to units of measurement, the SI was formalised in 1960. The foundation of the SI is the set of seven well defined base units: the metre, the kilogram, the second, the ampere, the kelvin, the mole, and the candela, from which all derived units (such as metres per second) are formed. On 16 November 2018 the 26th General Conference on Weights and Measures (CGPM) met in Versailles, to discuss and vote on the redefinition of four of the SI’s seven base units: the mole, the ampere, the kelvin, and the kilogram. This change, effective from 20th of May 2019, is perhaps the most fundamental change in the SI since its inception.

For the first time the SI will be defined entirely in terms of fundamental physical constants, instead of requiring the maintenance of a physical artefact. In this seminar I will explains why this re‐definition came about and what implications this might have for measurement science.