The definition of kilogram has changed forever - and what it means to us

Standard kilogram

"If you tell aliens that your civilization's units of measurement depend on an old piece of iron in a museum, you will become the laughing stock of the universe." As agreed last year, scientists are launching a procedure for abandoning the binding to physical standards to determine the units of measurement. Now the famous "Le Grand K" bar in the Paris Chamber of Weights and Measures, which is the standard of the kilogram, is nothing more than an artifact and a monument to science of the past.

The reasons why scientists decided to change the units of measurement are simple. Since 1889, the time of the creation of the standard kilogram, we have learned enough about the laws of the world order to draw a conclusion about the vulnerability of any physical objects. As well as measuring instruments based on them - even microscopic changes, from pressure drops to a speck of oxide on the metal, already affect the measurement accuracy. We need a new standard that will be the same at any point in the Universe where a person can get - even in the distant future.

Therefore, instead of binding a kilogram to a metal standard, a new, universal definition was invented for it. It is based on Planck's constant, a fundamental constant whose accuracy and reliability has been proven many times since its discovery in 1900. The works of Einstein and Planck made it possible to establish a connection first between energy and mass, and then between mass and Planck's constant.

If there is a natural connection between mass and Planck's constant, then the kilogram, as a unit of mass, can be expressed through this constant. The catch is in the details - the description contains a number with many decimal places and complex degrees, so scientists are now developing a simpler version for everyday use. Well, for those who are interested in calculating everything on their own - here is the value of the Planck constant according to the new rules of May 20, 2019: 6, 626070150 × 10 -34 kg⋅m 2 / s

Installation NIST-4, which is used to measure the Planck constant