Silicon-28 sphere is the latest contender in the physical weight game
It is officially defined as the mass of a 122-year-old cylinder of platinum and iridium, kept at theInternational Bureau of Weights and Measures(BIPM) in Paris. Yet the cylinder's mass seems to be changing as it ages, prompting several groups of scientists to seek a replacement. They hope to define the kilogram by referring to a physical constant rather than an antique object.
The new entire is shown above. The team has measured the number of atoms in a sphere of silicon-28 to calculate Avogadro's constant to nine significant figures: 6.02214084(18) × 1023 mol−1