Scientists on Friday voted to redefine the value of a kilogramme in a historic decision they say will improve the accuracy of scientific measurements, AP reported. More than 50 nations unanimously approved changing an international 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.
A kilogramme since 1889 has been defined as the mass of a cylinder of platinum-iridium alloy known as the International Prototype of the Kilogram and nicknamed “Le Grand K”. It is kept in a high-security vault at the headquarters of the International Bureau of Weights and Measures in France.
The member-nations of the International Bureau of Weights and Measures on Friday redefined a kilogramme in terms of a fixed numerical value called the Planck constant, which is derived from quantum physics. The update will come into effect from May 20.
Seven main units of measurement are currently in use, including the metre for length, the kilogramme for mass, the second for time, the ampere for electric current, the kelvin for temperature, the mole for the amount of a substance, and the candela for luminous intensity. Of these seven, the kilo was the last unit still based on a physical artefact.
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.
“We live in a modern world. There are pollutants in the atmosphere that can stick to the mass,” Reuters quoted a specialist in the engineering, materials and electrical science department at Britain’s National Physical Laboratory Ian Robinson as saying.
“So when you just get it [the International Prototype of the Kilogram] out of the vault, it’s slightly dirty and the whole process of cleaning or handling or using the mass can change its mass. So it’s not the best way, perhaps, of defining mass.”
Unlike the old physical measurement, the new “electric kilo” formula cannot accumulate particles of dust and pollution, decay over a period of time time, or be dropped and damaged. It is also easier to share.
Countries until now were also occasionally forced to send their own kilogrammes to France to be checked against the Le Grand K to see whether their mass was still accurate.
“If we stay where we are, and someone did accidentally drop the kilogram or if there was a contamination that we couldn’t control, then the whole system has got no head,” said Barry Inglis, a scientist from Australia. “That’s the thing that’s really been worrying us for maybe 15 years or more is just how vulnerable the system is, by depending just on that one little piece of platinum-iridium.”
Nobel Prize-winning American physicist William Phillips called the update “the greatest revolution in measurement since the French revolution,” which ushered in the metric system of metres and kilogrammes.