Nearly 130 Years Later, The Kilogram Gets A New Definition

At a meeting of the General Conference on Weights and Measures in Versailles, France, representatives from over 60 countries in France voted to redefine the kilogram, in favour of defining it in terms of an electric current.

Currently defined by the weight of a Platinum-based ingot called ‘Le Grand K’, it will henceforth be based on the ‘Planck’s Constant’, which describes the behaviour of elementary packets of light known as Photons. The new system will define the kilogram through an electrical force needed to counteract the weight of a kilogram on a machine called a Kibble balance.

Speaking to the Guardian, Stephan Schlamminger, a physicist from the US National Institute of Standards and Technology who has worked on redefining the kilogram for years said, “The vote went through unanimously. It was very emotional. They did a roll call of each country. One got a sense of how big metrology is.”

Many called the redefinition a ‘landmark move in scientific progress’. “Using the fundamental constants we observe in nature as a foundation for important concepts such as mass and time means that we have a stable foundation from which to advance our scientific understanding, develop new technologies and address some of society’s greatest challenges,” said Martin Milton, director of the International Bureau of Weights and measures.

As a result, units for electric current (ampere), temperature (Kelvin) and amount of substance (mole) will also be redefined. As per the old system, all replica kilograms had to be tested against the Le Grand K. However, with the new system, anyone with a Kibble’s balance can check their weights anytime anywhere.