Kilogram gets a new definition

On 16 November 2018, at the landmark, 26th General Conference on Weights and Measures (CGPM) in Versailles, France, representatives of 60 states adopted new definitions of the kilogram, the ampere, the kelvin and the mole.

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As of this date, the redefined International System of Units (SI) will be based on the fundamental constants of nature. The kilogram has been redefined by the Planck constant (h), the ampere in terms of the elementary electrical charge (e), the kelvin by the Boltzmann constant (k), and the mole by the Avogadro constant (NA).

The proposal of the redefined International System of Units (SI) was presented by the Director of the International Bureau of Weights and Measures (BIPM) who 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.“

„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. “

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A total of 60 countries voted for the adoption of the new definitions. At the conference, Montenegro was represented by Goran Vukoslavović, Associate Director at the Bureau of Metrology. Montenegro has been a full member of the BIPM since January 2018, which had enabled it to vote on all of the proposed resolutions at the meetings of the General Conference on Weights and Measures (CGPM).

During the Conference, renowned world scientists have presented their research. A Nobel Prize winner, Klaus von Klitzing from the Max Planck Society, spoke on the subject of „Quantum Hall Effect and Revision of the International System of Units“. Jean-Philippe Uzan from the French National Center for Scientific Research (CNRS) emphasized the role of the Planck constant in physics, while Jun Ye, a scientist from the American National Institute for Standards and Technology (NIST) and University of Colorado Boulder (JILA) talked about the optical atomic clocks and the new possibilities in the „quantum world“. Another Nobel Prize winner in Physics, Bill Phillips, from NIST explained how measurements are performed with fundamental constants and how the new redefined International System of Units is going to be used.

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Accurate and precise measurement, as of this day, will no longer rely on the use and comparison with physical objects. The kilogram, for example, had for the last 130 years been defined as being the mass of the International Prototype of the Kilogram, a cylinder of a platinum alloy stored at the BIPM. Stability and consistency of the kilogram during this period could only be confirmed by comparisons with identical copies, which is a difficult process and potentially inaccurate.

The new definitions will ensure stability and consistency of the International System of Units (SI), enabling the development of new, above all, quantum technologies. The new definitions will have a strong impact on the development of technology, international trade, the safety of healthcare systems and environmental protection.

The remaining SI units, the second, the metre and the candela have already been redefined in terms of the constants of nature.

The new definitions of the International System of Units will take effect on 20 May 2019, on the occasion of the next World Metrology Day.