20th May (UPI) – The kilogram is no longer defined by a physical object. Instead, the unit of measurement is now based on fundamental constants, atomic properties, and physical absolutes.
Scientists around the world can reproduce the mass constant.
Previously, one kilogram unit was based on the mass of a platinum-iridium alloy cylinder. The cylinder housed in Paris has been the standard bearer for the basic mass for 130 years.
Of course, physical objects change. Each time the cylinder was pulled out of the warehouse to calibrate an instrument, the object shed a handful of atoms. In the last 1
The physical kilogram task was officially announced on May 20, 2019. This is the World Metrology Day, a celebration of the Meter Convention of 1875, at which the scientific leaders agreed on the International System of Units.
With the official change of the definition of the kilogram and changes in the definitions for the basic units charge, temperature and mole, all international units are now defined by physical constants. Other common units, such as the meter, made the switch years ago.
"The [International System of Units] is now based on a set of definitions, each associated with the laws of physics, and has the advantage of being able to take into account further improvements in measurement science and technology to meet the needs of future users for many Years, "scientists in the Meter Convention said in a press release.
The definition of a kilogram is now based on the Planck constant, which is based on the energy of a photon to its frequency. A single kilogram equals 6,62607015 times 10 ^ 34 kilograms per square meter per second.
Nobel laureate Wolfgang Ketterle, professor of physics at MIT, explained the change in a lecture on the World Metrology Day on Monday.
"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 the cesium atomic clock," says Ketterle.
The change does not mean that scientists now have to count photons. As Ketterle explained, there is a multi-step process to precisely define one kilogram using physics and mathematics.
"If you win a million dollars and pay it in pennies, you do not want to count pennies." In metrology, something analogous is exchanged by comparing the atomic clock frequency of the US dollar and the US dollar into $ 100 and then counted, "Ketterle told MIT News cesium atoms at a much higher atomic frequency, then measure the mass of the electron or a single atom at that frequency and then start counting," he said.