Starting this Monday, the kilogram will cease to be what it was – 19/05/2019

The kilogram is one of the four basic measurement units – as well as the ampere, kelvin and mol- that were redefined last year at the General Conference of Weights and Measures (GFCM). This change is the most important revision of the International System of Units since its inception in 1960. This Monday is in effect. Now, the weight unit will be defined by fundamental and non-arbitrary constantsas it was until now.

This redefinition does not affect everyday life. In the warehouse, the kilo will have the same weight. Instead, he has a great importance for scientific research which require a high level of precision in their calculations.

Héctor Laiz is responsible for metrology, quality and the environment of INTI, president of the inter-American metrology system and member of the International Committee of Weights and Measures. In November, on behalf of Argentina, he was one of 18 experts who voted in favor of the GFCM amendment. In dialogue with Clarin, explain that "the kilo will continue to weigh a kiloWhat changes is how we define a kilogram because advances in science and technology are changing the way humans define units of measurement. "

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In this regard, he recalled that "the kilogram It was created in 1875 at the subway convention. "

From Monday, the day of the World Metrology Day, the kilo will be defined in relation to the Planck constant, central in the theory of quantum mechanics and named after one of his parents, the German physicist and mathematician Max Planck. It's a physical constant considered invariable, with a dimensionless and universal value that can be reproduced in the laboratory without being subjected to a physical object.

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Until now the unit of weight was defined according to an object: a kilogram was equivalent to the mbad that has a cylinder of 4 centimeters of platinum iridium manufactured in London and placed under the responsibility of the International Bureau of Weights and Measures (BIPM, for its acronym in English), saved since 1889 in a chest in France.

But there is a disadvantage: this original kilo lost in a microgram of the 50th century. Indeed, objects can easily lose atoms or absorb molecules from the air. Therefore, using one to define a unit of measure is complicated.

"From now on, all units will be defined based on constants of nature, instead of artifacts, material properties or unrealistic theoretical experiences, as is happening today This will allow scientists who work with the highest level of accuracy, run the units in different places or moments, with any relevant experience and in any scale value, "Laiz emphasizes.

With the system that was in effect until Sunday, it was necessary to send every five years to "calibrate" the kilo samples that were in Argentina – objects similar to that of France – to the Office Parisian weights and measures. INTI technicians did what they call a "spread" in multiples and submultiples to be able to weigh tons to micrograms.

"We calibrated five weights of one kilogram, then two of five, with two of five, one of ten, and so on until we reach 1,000 kilograms," says Laiz. "With a weight of 1,000 kilos, we calibrate the hoppers weighing the products of the field transported by the boats.When we say that Argentina has exported 40 million tons of grain, we measure them with these weights."

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Now, with the new definition, it will no longer be necessary to calibrate our model against the international. And local technicians will be able to calculate the kilogram here. In fact, five institutes around the world have already carried out unofficial calibrations in recent years on the basis of the new definition. One of them is the National Institute of Standards and Technology (NIST) of the United States. There is a watts scale that measures the Planck constant with an error of 34 parts per 1,000 million. This experience is one of those that allowed the current redefinition of the kilogram.

Alejandra Tonina, physical physician and head of the Department of Quantum Metrology at INTI, said that in her region, this redefinition is fundamental. "Previously, the electrical quantities, like the ampere, were defined with the international system, which consisted of an experiment very difficult to carry out and entailed a lot of uncertainty, it's mistakes. We are now using much more precise nature constants, "said the expert.

DD