Perfect silicon spheres were developed to redefine the kilogram because the platinum kilogram was changing in weight even in extremely strictly controlled physical conditions. If dust can ruin the platinum kilogram, why are people allowed to touch the silicon version?

Question

How is it that the sphere doesn’t become ‘contaminated’ with extra atoms from skin, clothes or even breath? Or is it just that these contaminants are very easy to clean off afterwards?

In: Physics

Answer 1

The sphere was an alternative approach to redefining the kilogram. It was an attempt to define Avogadro’s constant, which relates the number of atoms or molecules in a substance to its mass. Because the sphere was made of one particular isotope of silicon, they were able to achieve an extremely precise measurement of its mass and thus a very accurate count of the atoms.

Ultimately, that was not the approach taken. The kilogram was instead defined with Planck’s constant which, as another commenter has correctly pointed out, defines it in terms of the meter and the second. Beyond that the discussion leaves the realm of ELI5.

Source: am metrologist.