In science news : "Kilogram, Ampere, Kelvin and Mole will be redefined"

On November 16, 2018, at a session of the 26th General Conference on Weights and Measures in Versailles, France, representatives of countries from around the world voted to finally re-define the metric system that has not been changed since 1983. It was a big day not only for metrologists but for all of us. 60 unanimous votes made a decision that will probably change global trade and technology forever. There will no longer be physical objects in the SI system.

Up until now, kilogram has been based on a platinum-iridium cylinder stored in France. Basically, the weight of that specific cylinder has been defined as the weight of one kilogram and all the scales and measurements have been calibrated in a way that the weight the same as the weight of that cylinder is one kilogram. The International Prototype Kilogram (Le Grand K) will still be monitored and studied but it will no longer have former scientific significance besides the historical one. From May 2019, the kilogram will be defined in terms of Planck’s constant, a number that relates a radio wave’s energy to its frequency.

Science needs to be understandable in all corners of the Earth. It needs to be standardized when it comes to units because you can not have something measured in one thing in one country and in another thing in a different country. You can when it comes to daily life but not when it comes to science.

That is why we have the International System of Units or SI (SI is abbreviated from the French Système international). It is built on seven base units, which are ampere, Kelvin, second, meter, kilogram, candela, mole, and a set of twenty prefixes to the unit names and unit symbols. The SI base units are the building blocks from which all the other units are derived. Maxwell first introduced the concept of a coherent system with three quantities as base units: mass, length and time, Giorgi later identified the need for an electrical base unit, and another three base units (temperature, amount of substance and luminous intensity) were added later. The derived units in the SI are formed by powers, products or quotients of the base units and are unlimited in number. When it comes to prefixes, there are twenty of them for the International System of Units, from yocto as the smallest to the yotta as the largest or from ten to the power of -24 to ten to the power of +24.

The big decision was made at the General Conference on Weights and Measures in Versailles, France, which was organized by the International Bureau of Weights and Measures (BIPM). All SI units will now be defined in terms of constants that describe the natural world. Physical objects will no longer define measurement units.

Before you start fantasizing how you will bench press 100 kilograms or buy more bananas for the same price, let me stop you right there and burst your delusional happy bubble. A kilogram will still be a kilogram, it will just be defined differently. The new definition will allow more accurate measuring of weight below one kilogram. The kilogram itself will be defined in terms of the Planck constant, guaranteeing long-term stability of the SI mass scale. It. The unit of mass will be defined through the electrical force needed to counteract the weight of a kilogram on a machine called a Kibble balance. That electric force is linked to the Planck constant through quantum electric effects. After May 20, 2019, the Planck constant will be fixed at exactly 6.62607015 × 10−34 kilograms times meters squared per second. The value of the Planck constant will ensure that there will be no change in the SI kilogram at the time of redefinition.

Science will no longer be limited by objects in the measurement of the world. We will have universality accessible units that will ensure even greater accuracy and accelerate scientific advancement. Just as the redefinition of the second in 1967 provided the basis for technology that has transformed our communications through GPS and the internet, these new changes will have a wide-reaching impact in science and technology. A cylinder of metal known as the International Prototype of the Kilogram, the last remaining physical artifact in the SI system will from next year become nothing more than a piece of history.