In a world where everything tends to become better, faster, higher and stronger, scientists from the Avogadro Project in Australia have reached a new peak: they created the world's most round object.
They did this 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 thanks to different physical laws and properties, a kilogram still remains attached to a particular physical object: a cylinder made of an alloy of platinum and iridium, created in 1889.
For example, a "meter" can be defined as the distance traveled by light in a tiny fraction of a second. In turn, the "second" is determined through the frequency of the transition between two hyperfine levels of the ground state of the cesium-133 atom. The "kilogram" is still measured as the physical mass of a sample hidden in a safe vault of the Paris Chamber of Mer and Libra.
For no apparent reason, and despite all possible precautions, the mass of the reference cylinder changes with 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 specimen copies of this cylinder, stored in different countries.
To solve the problem of creating an unchanged standard kilogram, the Australian Center for Precision Optics, in which the Avogadro Project is based, created an almost perfect sphere of silicon of very high purity and stability. Calculating the size and weight of the sphere, scientists can determine the exact number of silicon atoms in it, thereby creating a constant in time standard of mass.
The scientists decided to give the standard a spherical shape, because it lacks corners and edges that can be damaged, besides, the sphere has only one parameter - the diameter - which must be measured to calculate its volume.
The manufacturing of the sphere took place in several stages. First in Russia, with the help of centrifuges for uranium enrichment, a very pure isotope of silicon-28 was obtained. The batch of this material was sent to the German National Metrology Institute, where, after six unsuccessful attempts, a cylindrical crystal was grown without defects. Then he was cut into 5 kg pieces and sent to Australia.
To give the silicon cylinders a spherical shape, Australians used two rotating rotors, which manually grinded the workpiece. This process took several months. After that, computer measurements were made using a laser, and the detected irregularities were removed purposefully.
If you increase this sphere to the size of the Earth, then its surface will have a ripple depth of 12-5 mm and a diameter of 3-5 m.
