Southampton Physics Colloquia

Artefact Free Measurement: the redefinition of the international system of units
Prof Graham Machin National Physical Laboratory 14:30, Friday 14 December 2018
Physics Seminar Room (Building 46/5081)
The international system of units (the SI) – namely the kilogram, the ampere, the kelvin, the metre, the mole, the second and the candela – have served the measurement requirements of the world for many years. Since the inception of the SI a number of the individual unit definitions have evolved to meet advancing measurement needs. However in November 2018 the General Congress of Weights and Measures (CGPM) will meet in Paris to usher in the most fundamental change the SI has ever had. The current semi-classical and partially artefact based unit definitions will give way to new definitions based on a set of fundamental constants with defined values. The objective of the redefinition is to ensure that the SI remains enduringly fit for purpose into the 21st Century and beyond. Prof Machin will introduce the current SI, explain the changes that are being made and their impact on measurement. Emphasis will be given to the changes affecting the kelvin and how the redefinition will open up the possibility of no-drift always-right sensors through the development of practical primary thermometry in the 2020s. The talk will be illustrated with real examples and artefacts.