Towards the new International System of Units
The world in which we live and work is marked by time and populated by objects with measurable quantities.
In the world in which we live, we expect the watches of people who have an appointment at a certain time in a certain place all to be set to the same time, or a kilogram of bread we buy from our local store to be equivalent to a kilogram of bread bought anywhere else.
These expectations are guaranteed by the International System of Units, a shared language, adopted by most countries around the world, which provides a common basis for trade, industry and science.
The universality and comparability of the measures we rely on today are not a given but the result of a still ongoing scientific and “diplomatic” process that began between the end of the eighteenth century and the second half of the nineteenth century to meet the need for a worldwide standardized system of measurement to encourage the exchange of knowledge, information and goods.
Today, this history is preparing for major changes with the adoption of the new International System of Units. The announcement was made during the event Il futuro prossimo dei pesi e delle misure, organized in Rome by the National Institute of Metrological Research (INRIM), the Italian public body active in measurement research.
The meeting, opened by a welcome speech from the INRIM President Diederik Wiersma and moderated by the science journalist Piero Bianucci, was attended by representatives of institutions and the scientific world, including the Deputy Minister of Education, University and Research Lorenzo Fioramonti.
The System of Units has been in constant evolution. For example, the type and number of the base units of measurement, from which all the other units derive, have changed over time until they became 7 – metre, kilogram, second, ampere, kelvin, mole, candela – corresponding to as many basic physical quantities: length, mass, time, electric current, thermodynamic temperature, amount of substance, luminous intensity.
An important stage in this history is the end of the use of physical objects – such as the famous platinum-iridium bar used to define the prototype metre until the end of the 1960s – and the adoption of more accurate references.
In particular, between 1967 and 1982, scientists redefined 3 base units of the International System, linking them to physical constants: quantities with immutable and universal values. The second was redefined in terms of hyperfine transition frequency of the caesium atom, the metre in terms of speed of light, and the candela in terms of luminous intensity.
The redefinition of the remaining 4 base units of measurement was agreed upon at the 26th General Conference on Weights and Measures held from 13 to 16 November 2018 in Versailles. Italy was represented by Maria Luisa Rastello, Scientific Director of INRIM.
The new system approved in Versailles redefines the kilogram in terms of Planck constant, the ampere in terms of elementary electrical charge, the kelvin in terms of Boltzmann constant, and the mole in terms of Avogadro constant. The changes will come into effect on 20 May 2019, World Metrology Day, which celebrates the science of measurement.
This is a major turning point in science but it will have a minimal impact on our lives, the experts say. However, it will pave the way for the new challenges that metrology is preparing to face in the immediate future: make the systems of measurement more solid in the main areas of scientific research and technological innovation, such as medicine and biology, energy, food processing and artificial intelligence, to name but a few. Because without the accurate measurement of quantities, also science staggers.