Kilograms, Amperes and Kelvins, Oh My

Just when you thought that some things were forever immutable, now comes word that the definitions of some critical weights and measures will soon be changed.

According to a report posted to Science Daily website, the General Conference on Weights and Measures voted in November to redefine the international system of units (SI), resulting in changes in the definition of the kilogram, the ampere, the kelvin and the mole. As of May 2019, these measurement units will no longer be defined by actual physical objects, but instead “in terms of constants that describe the natural world.”

Specifically, the changes are:

  • Kilogram—will be defined by the Planck constant (h)
  • Ampere—will be defined by the elementary electrical charge (e)
  • Kelvin—will be defined by the Boltzmann constant (k)
  • Mole—will be defined by the Avogadro constant (NA)

The changes are reportedly intended to “assure the future stability of the SI and open the opportunity for the use of new technologies, including quantum technologies, to implement the definitions.”

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