Scientists set to change definition of the kilogram

Scientists Will Vote Tomorrow to Change the Definition of Kilogram

Scientists Will Vote Tomorrow to Change the Definition of Kilogram

More than 50 nations unanimously approved changing an global measurement system to redefine the kilogramme, which measures mass, and a few other units including the ampere, kelvin and mole, at a meeting in Versailles.

The redefined kilo is expected to allow for more accurate measurements of extremely small or very huge masses as until now, the weight of a kilogramme could change over time due to factors like pollution and everyday wear and tear.

Currently, a kilo is defined by the weight of Le Grand K, a mix of 90 per cent platinum and 10 per cent iridium hailed as the "perfect" kilogram since the late 1800s. Today knowing that a kilogram is a kilogram is done with a set of worldwide prototype kilogram weights made from very hard metals like platinum, but even that isn't entirely accurate.

Other units that are set to be redefined include the ampere (electric current), the kelvin (heat) and the mole (particle numbers).

World scientists for whom the update represents decades of work clapped, cheered and even wept as the 50-plus nations one by one said "yes" or "oui" to the update.

For the average person, however, the new definition shouldn't make much of a difference. Bathroom scales won't suddenly get kinder and kilos and grams won't change in supermarkets.

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Nations gathered in Versailles, west of Paris, instead approved the use of a scientific formula to define the exact weight of a kilogram.

The Grand K and its six official copies, kept together in the same safe on the edge of Paris and collectively known as the "heir and the spares", will be retired but not forgotten.

Unlike the old physical measurement, the new "electric kilo" formula can not accumulate particles of dust and pollution, decay over a period of time time, or be dropped and damaged.

The bureau is the guardian of the system, as well as of Le Grand K and its copies, which are stored in a vault that requires three keys, kept by three different people, to unlock. Scientists want to keep studying them to see whether their masses decay over time.

The metal kilo is being replaced by a definition based on Planck's constant, which is part of one of the most celebrated equations in physics but also devilishly hard to explain.

So the scientists gathered Friday at the General Conference on Weights and Measures chose to retire Le Grand K and move on to something that couldn't be changed: the mathematical concept known as Planck's constant.

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