The world’s definition of the kilogram is forever changed

International System of Units overhauled in historic vote.


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To make a milestone in the science of measurement, representatives from 60 nations voted to redefine the International System of Units (SI), changing the word’s meaning of the kilogram, the ampere, the Kelvin and the mole, until the end of time. It means all SI units will be defined in terms of constants that describe the natural world.

This milestone will guarantee the future stability of the SI and open the door for the utilization of new advancements, including quantum technologies, to actualize the definitions. Reports suggested that the changes will come into force on 20 May 2019.

Untill now, the kilogram is defined as the being equal to the mass of the International Prototype of the Kilogram (IPK), a cylinder of a platinum alloy stored at the BIPM in France. But now, it will be retired and replaced by the Planck constant — the fundamental constant of quantum physics. The Planck constant is ready for use everywhere and always.

The new definitions impact four of the seven base units of the SI: the kilogram, ampere, kelvin and mole; and all units derived from them, such as the volt, ohm, and joule.

  • The kilogram — will be defined by the Planck constant (h)
  • The ampere — will be defined by the elementary electrical charge (e)
  • The kelvin — will be defined by the Boltzmann constant (k)
  • The mole — will be defined by the Avogadro constant (NA)

Martin Milton, Director, International Bureau of Weights and Measures (BIPM) said, “The SI redefinition is a landmark moment in scientific progress. Using the fundamental constants we observe in nature as a foundation for important concepts, such as mass and time, means that we have a stable foundation from which to advance our scientific understanding, develop new technologies and address some of society’s greatest challenges.”

Barry Inglis, Director of the International Committee for Weights and Measures said, “Today marks the culmination of decades of work by measurement scientists around the world, the significance of which is immense. We will now no longer be bound by the limitations of objects in our measurement of the world, but have universality accessible units that can pave the way to even greater accuracy, and even accelerate scientific advancement.”

Despite the fact that the measure of these units won’t change (a kilogram will, in any case, be a kilogram), the four reclassified units will join the second, the meter and the candela to guarantee that the arrangement of SI base units will keep on being both steady and helpful.

The revised SI will keep up its significance by encouraging specialized developments. Similarly, as the redefinition of the second in 1967 gave the premise to innovation that has changed how we impart over the globe, through GPS and the web, the new changes will have wide-achieving sway in science, technology, trade, health, and nature, among numerous different divisions.


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