Definition of kilogram changes from May 20, 2019- What this means

Scientists have changed the way the kilogram is defined. Photo: Courtesy
For over 130 years since its establishment in 1889, Kilogram has been defined by the weight of a platinum-based ingot called "Le Grand K" which is locked away in a safe in Paris under two bell jars in a climate-controlled vault.

In November 2018, during the General Conference on Weights and Measurements, researchers who met in Versailles voted in favour of a new definition of kilogram basing on an electric current.

But as scientists and other stakeholders mark the World Metrology Day today – 20 May - it also marks the beginning of defining all SI units basing on the fundamental constants of nature.

What this means

This means that kilogram will be redefined based on the ratio of energy to frequency of the photon, scientifically referred to as the Planck constant.

Before being voted out, a kilogram was the only SI unit still defined by a physical object.

According to Science alert, Emeritus Director of the International Bureau of Weights and Measures (BIPM) Terry Quinn to Science alert says: “the idea is that having all units based on the constants of physics, they are by definition stable and unaltered in the future and universally accessible to everywhere.”

Quinn also adds that the new definition aims at improving the understanding and accuracy of teaching about units.

"It will open up the way to unlimited improvements in the accuracy of measurements, it will improve greatly the accuracy and extend the possibilities of making accurate measurements at very small and very large quantities," Said Quinn as quoted by science alert.

To a common man, these changes make no recognizable difference since a kilogram of meat or sugar will still remain a kilogram of sugar or of meat.

But in the world where accurate measurement is needed in areas such as drug development, nanotechnology and precision engineering, scientists responsible for maintaining the international system had no alternative but to phase out Le Grand K to a more robust definition.

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KilogramSI unitsWorld Metrology Day