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May 20 (UPI) – The kilogram is no longer defined by a physical object. Instead, from now on, the unit of measurement will be based on fundamental constants, atomic properties, and physical absolutes.
Scientists around the world will be able to reproduce the mass constant.
Until now, a kilogram unit was based on the mass of a platinum-and-iridium alloy cylinder. Installed in Paris, the cylinder has been the flag-bearer of the base unit of the mass for 130 years.
Of course, physical objects change. Whenever the cylinder was out of the store to calibrate an instrument, the object was throwing a handful of atoms. Over the past 130 years, the cylinder has lost 50 micrograms.
The abandonment of the physical kilogram was formalized on May 20, 2019, on the occasion of the World Metrology Day, a celebration of the Meter Convention held in 1875, during which scientific leaders agreed of the International System of Units.
With the official change of the kilogram definition, as well as the changes to the base load, temperature, and mole definitions, all international units are now defined by physical constants. Other common units, like the meter, made the switch years ago.
"The [International System of Units] is now based on a set of definitions, each related to the laws of physics and having the advantage of being able to bring further improvements in the science and technology of measurement to meet the needs of future users for many years ", said the scientist at the Meter Convention announced in a press release.
From now on, the definition of the kilogram will be based on the Planck constant, based on the energy of a photon at its frequency. A single kilogram equals 6.62607015 times 10 ^ 34 kilograms times the square meters per second.
Nobel laureate Wolfgang Ketterle, professor of physics at MIT, explained the change at a conference Monday on the occasion of World Metrology Day.
"Conceptually, the explanation is that 1 kg is now the mass of a defined number of photons, 1.4755214 * 10 ^ 40, at the frequency of cesium atomic clock", according to Ketterle.
Change does not mean that scientists will now have to count photons. As Ketterle explained, there is a multi-step process that uses physics and mathematics to accurately define a kilogram.
"If you win a million dollars and you pay money, you do not want to count the pennies, you will first exchange the pennies in dollar bills and then the dollar bills." in 100 dollar bills, then you'll count them, "Ketterle told MIT News.
"In metrology, something analogous is done by comparing the atomic clock frequency of cesium atoms to a much higher atomic frequency.You then use this frequency to measure the mass of the electron. or a single atom, and then you start counting, "he said.
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