The Kilogram- Redefined

As of 16th November 2018, the Kilogram has been redefined. On this day 0ne by one, the representatives of more than 60 Nations voiced their vote at the 26th meeting of the General Conference on Weights and Measures in Versailles, France to redefine the kilogram. and unanimously decided that from this day on, the measure will be based on Planck’s constant.

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

This is indeed a very big moment for the scientific community because since 1889 the definition of the kilogram was based on a shining 4centimeter long cylinder, nicknamed Big K, and locked in the vault of the International Bureau of weights and measures (BIPM) in France. For reference 6 other identical copies of Big K are kept alongside it that measure exactly the same. And scientist further made identical copies of it for researchers around the world to use. The big K as only been taken out of the vault only 3 times in these 130 years to be re-calibrated with its identical copies. This chunk of metal defined what the Kilogram actually was for all these years. Everything from bathroom scales to precise scientific weighing devices depended on this.

The Kilogram is one of the seven fundamental units in the International System of Units (SI). It might not sound that important. But these form an integral part of Science and Technology and are the basis of measurements. They ensure uniformity and stability in scientific innovation, manufacturing, health industry and more and thus as a whole helps the global economy to function smoothly. For all these years Big K got the job done but there was a fundamental problem. It was seen that over the years the big K seemed to be losing weight. (Or its identical copies were getting heavier as time passed). But whatever the case, the concern here was that there was a deviation. This means that is was unreliable. If theoretically someone came and cut the cylinder (big K) in half its mass would still be equal to one kilogram because 1 Kg is equal to Big K and not the other way around. If Big K changes measuring instruments and tools all around the world would have to adjust accordingly.

The difference in mass of big K to its identical closes was about 50 micro-grams which are about the mass of an eyelash. A very tiny deviation of the everyday world but can have a significant impact on precise scientific measuring measurements and experiments where accuracy is key.

To reduce this uncertainty and resolve the issue the conference passed a unanimous decision to base the value of the kilogram to a fundamental constant known as the Plank’s constant which defines the smallest possible unit of energy. It is a constant value that will hold across space and time, unlike the inconsistent metal cylinder that was used all these years. “Today marks the culmination of decades of work by measurement scientists around the world, the significance of which is immense,” said Barry Inglis, director of the International Committee for Weights and Measures. “We will now no longer be bound by the limitations of objects in our measurement of the world, but have universality accessible units that can pave the way to even greater accuracy, and even accelerate scientific advancement.”

With Planck’s constant and an instrument called the Kibble balance researchers can now measure the kilogram to an accuracy of +- 10-8 which is around one-fourth of the weight of an eyelash. Schlamminger says. “That’s the thing in science—there’s no such thing as perfection,” he says. “There’s always random effects, and there’s always a little bit of scatter. And you have to decide: Is it good enough?”. And seeing the unanimous decision take we have to say that for now, it is.

This change will officially go into effect from 14th of May 2019. So, will this have any dramatic effect on our everyday lives and the world around us? Not really but it will be a significant difference and have practical applications in fields that depend on meticulous measurements like the medical, electronics and nano-manufacturing industries.



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