Kilogram, Amp and Kelvin Redefined in Largest Units Overhaul Since 1875

Representatives from 60 countries have voted to redefine the International System of Units in terms of constants that describe the natural world.

A historic decision was taken this week at the General Conference on Weights and Measures in Versailles, France, organized by the International Bureau of Weights and Measures (BIPM), which marks the biggest overhaul of the International System of Units (SI) since 1875. 

Science

No One Knows How Much a Kilogram Actually Weighs

At a meeting on 16 November, representatives from 60 countries voted to redefine the SI in terms of constants that describe the natural world. The result is that the definitions of the kilogram, the ampere, the kelvin, and even the mole will soon be forever altered!

"The SI redefinition is a landmark moment in scientific progress," said Martin Milton, Director, BIPM. "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."

Adapting with the times

The changes are scheduled to come into effect on May 20th of next year. The move will see the end of physical objects used to define measurements in what is an attempt by the BIPM to cement the SI's future stability by adapting it to keep up with the evolution of new technologies. 

"Today marks the culmination of decades of work by measurement scientists around the world, the significance of which is immense," said Barry Inglis, Director of the International Committee for Weights and Measures. "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."

More stable measurements

The overhaul will see new definitions applied to four of the seven base units of the SI, as well as all units derived from them. It will also see the introduction of more stable measurements.

For instance, the International Prototype of the Kilogram (IPK), a cylinder of a platinum alloy stored at the BIPM in France whose stability required often inaccurate comparisons with identical copies, will be retired and replaced by the Planck constant, quantum physics' fundamental constant that is ubiquitously available.

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The ampere will also now be defined by the elementary electrical charge (e), the kelvin by the Boltzmann constant (k) and the mole by the Avogadro constant (NA). The size of the units will remain unchanged, however, to further improve stability, the four redefined units will join the second, the meter and the candela.

kilogram SI units redefined overhaul
Source: Nature

The new system will enable much more precise measurements of very large and very small masses. It is also designed to facilitate today's constant technical innovations.

Perhaps the biggest advantage of the overhaul, however, is that now any experiment will be able to be used to determine the units. This will result in a more democratic system and that is something we can definitely get behind!

Via: NPL

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