"The world's most circular object" can become a new kilo measure

In a world where everything tends to become better, faster, higher and stronger, scientists from the Australian Project Avogadro have reached a new peak: they have created the world's most circular object.

They did it not for the sake of the fact, but in an attempt to solve the " kilogram problem ". Unlike other measures that can theoretically be measured anywhere due to different physical laws and properties, the kilogram is still tied to a specific physical object: a cylinder made of an alloy of platinum and iridium , created in 1889.

For example, "meter" can be defined as the distance traveled by light in a tiny fraction of a second . In turn, the “second” is determined by the transition frequency between two ultrafine levels of the ground state of the cesium-133 atom . "Kilogram" is still measured as the physical mass of a sample hidden in a safe repository of the Paris Chamber of Measures and Scales .
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For unknown reasons, and despite all sorts of precautions, the mass of the reference cylinder changes over time. In other words, today the kilogram sample weighs less than after its smelting 125 years ago. This is confirmed on the basis of comparisons with 40 samples, copies of this cylinder, stored in different countries.

To solve the problem of creating a constant kilogram standard, the Australian Center for Precise Optics , in which the Avogadro Project is based, created an almost perfect sphere of very high purity and stability silicon. By calculating the size and weight of the sphere, scientists can determine the exact number of silicon atoms in it, thereby creating a mass standard unchanged in time.

Scientists decided to give the standard the shape of a sphere , because it is devoid of corners and edges that can be damaged, and besides, the sphere has only one parameter — the diameter — which needs to be measured to calculate its volume.

The production of the sphere took place in several stages. First, in Russia, using centrifuges to enrich uranium, a very pure isotope of silicon-28 was obtained. A batch of this material was sent to the German National Institute of Metrology, where, after six unsuccessful attempts, a cylindrical crystal was grown without defects. Then he was cut into pieces of 5 kg and sent to Australia.

To make the silicon cylinders spherical in shape, the Australians used two rotating rotors, with which they manually ground the workpiece. This process took several months. After that, computer measurements were performed using a laser, and the detected irregularities were removed purposefully.

If we increase this sphere to the size of the Earth, then on its surface there will be ripples 12-5 mm deep and 3-5 m in diameter.

To be fair, another method of creating a kilogram standard, the so-called “ watt balance ”, should be mentioned. The essence of the method lies in the fact that a special installation calculates the force that is needed to counterbalance a load of one kilogram and determines how much it is a watt of electricity.