Scientists set to change definition of the kilogram

Lester Mason
November 18, 2018

After a week-long meeting at the Palace of Versailles, outside Paris, BIPM members chose to "bring an end to the use of physical objects to define measurement units", and update definition for the kilogram in terms of constants that "will open the opportunity for the use of new technologies, including quantum (ones)". It also is expected to be more accurate when measuring very, very small or very, very large masses.

In 2013, scientists discovered that the kilogram Prototype had gained tens of micrograms of mass from surface contamination.

But why change the kilogram at all?

In May 2019 when the revised definition of the kilogram is implemented, it will be based on three fundamental constants: the Planck constant, the speed of light and the cesium atom's natural microwave radiation.

Scientists have voted to change the definition of a kilogram after more than 100 years in a landmark decision.

Now kg is supposed to be measured by the so-called Watt scales (or balance of the Kibble) - this instrument determines the mass via Planck's constant, the basic constant of quantum theory. Now all SI units are tied to a fundamental physical constant.

Perdi Williams from the National Physical Laboratory said: "The new system is going to work a lot better".


"We put in place a system that doesn't depend on something that is 140 years old", Milton said.

The metric system - or, as it is known today, the International System of Units (SI) - is an fantastic achievement of mankind. Many in the room were especially anxious to say goodbye to the worldwide prototype of the kilogram, which was created in 1889.

Scientists have dreamed of having an accurate and precise measurement system that could be realized anytime, anywhere, since the 1700s. "So even though Le Grand K is fit for objective at the moment, it won't be in 100 years' time", he tells BBC. Though the change in mass is roughly equivalent to the weight of an eyelash, there could be wide repercussions.

Members of the BIPM, which groups some 60 nations, agreed on Friday after a week-long meeting at the nearby Palace of Versailles to redefine a kilogram in terms of a tiny but unchanging value called the 'Planck constant'.

It is noted that every few decades all copies of the kilograms in the world had to be checked. The machine measures the weight of an object by the strength of the electric current and voltage required to produce a compensating force, equalising one force with another.

It was originally called a "watt" balance, the SI unit of power.

Taken in 1901, the official definition of exactly what was "the Kilogram is a unit of mass equal to the mass of the global prototype of the kilogram". It is kept in a high-security vault at the headquarters of the International Bureau of Weights and Measures in France. This mass was then represented by a cylinder - the prototype that was adopted as a unit of weight by other countries.

Other reports by Iphone Fresh

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