In a luxurious building in the suburbs of Paris, in a sealed box with a vacuum seal, under three glass domes, hidden small metal cylinder the size of a palm, known around the world as the international prototype Kilogram, or «Le Grand K«. Created in 1879 from an alloy of platinum and iridiumcylinder was called the «perfect» kilogram — the gold standard by which scientists evaluate all other kilograms.
Despite the fact that basic measurements using tangible benchmarks showed improvement, using physical standards, like everything in our world has its disadvantages. No matter how perfect, neither was the standard, he has the ability to change. For example, Le Grand K is losing weight. At his final weigh-in in 1988, it was discovered that the error is 0.05 milligrams – that weighs as much a grain of sand. Experts are not sure what happened to this mass, but there is a theory that due to frequent handling, the cylinder could become a little easier. Others believe that the alloy Le Grand K is decontamination, which means that the air is gradually emerging from the metal.
Whatever the reason for the gradual reduction of Le Grand K, the scientists aim to obtain more reliable standard. Some of them say that it should have been done long ago, since all other units of measure already determined fundamental natural constants that can be reproduced anywhere anytime (provided that you have the necessary laboratory equipment).
However, standardization kilograms proved to be a challenging undertaking. Australian scientists, for example, are polished sphere of silicon with a mass of 1 kg, in the hope that they will be able to count the number of atoms which it contains, to create a more accurate standard.
American physicists at the National Institute of standards and technology (NIST) decided to go the other way. They are trying to redefine the kilogram in terms of a number of voltage needed to lift the weight.
John Pratt and his team said Friday that they have obtained the most precise measurements in the world, necessary for this purpose. Pratt says that this achievement, although seems insignificant, can change the definition of kilograms, replacing the concept of the XIX century on the concept or even XXI XXII century. Now kilograms might be based more on the idea rather than a specific material object.
Scientists agree that it’s time to send the Le grand K to resign. The use of technology of the XIX century to the XXI century physics, like trying to get to Mars on a rocket with a steam engine. It is obvious that this approach simply won’t work.
So in 2014 at the General conference of weights and measures, the scientific community has decided to revise the definition of the kilogram based on Planck’s constant from quantum mechanics, linking the value of energy quantum of electromagnetic radiation with its frequency. If physics you get a pretty good measurement of Planck’s constant, they calculate the value of kg due to this indicator.
The difficulty lies in the fact that Planck’s constant is very difficult to measure. Pratt and his colleagues at NIST have spent most of the last few years to get accurate enough numbers to cater to the scientific community.
They used a special tool Wachovia scales, which is due to electromagnetism. An electric current is sent through the coiled wire, creating a magnetic field that in turn creates the force, moving up, necessary for the balance of the scale. Scientists can find out the strength of this field, pulling the coil. If you know the voltage, current and speed, which was stretched coil, you can calculate the Planck constant with precision. The study took 16 months, resulting in the team Pratt calculated Planck’s constant.
The Committee of weights and measures will meet this month to set the global value of Planck constant by averaging the values calculated at NIST and other laboratories. In 2018, next General conference of weights and measures, the scientific community will create a resolution on the revision of the kilogram on the basis of this constant.
