Tag Archives: Planck’s Constant

Scientists just got one of the best measures yet of a fundamental of physics

Beneath three glass bell jars, in a locked vault in the basement of a highly secure facility outside Paris, sits the world’s most important kilogram.

The NIST-4 Kibble balance. The instrument was used to calculate Planck’s constant, an important step toward redefining the kilogram. (Jennifer Lauren Lee/NIST PML)
The NIST-4 Kibble balance. The instrument was used to calculate Planck’s constant, an important step toward redefining the kilogram. (Jennifer Lauren Lee/NIST PML)
Ever since 1889, when the General Conference on Weights and Measures (CGPM) made the imperious pronouncement, “this prototype shall henceforth be considered to be the unit of mass,” this platinum and iridium cylinder has served as the standard by which all other kilograms are measured, from the weights on a high-tech lab scale to the plastic discs high schoolers use in chemistry class. It’s known as “le Grand K,” and it’s afforded the security and scrutiny befitting such a fancy title. Even the researchers who work with it can’t touch it, lest their fingertips wipe away atoms or leave residue on the gleaming surface. The vault containing the cylinder can only be opened by gathering three custodians carrying three different keys, and that’s happened fewer than a dozen times in the kilogram’s 127-year history.  Continue reading Scientists just got one of the best measures yet of a fundamental of physics