The kilogram, one of the seven base units of the International System of Units (SI), is set to be redefined in terms of a fundamental constant of nature – the Planck constant (h). This change, which will take effect on May 20, 2019, marks the first major overhaul of the SI since its inception in 1960.
The decision to redefine the kilogram using the Planck constant was made by the international measurement science community after decades of debate. The connection between mass and the Planck constant is rooted in the deep underlying relationship between Einstein’s famous equation E=mc^2 and Planck’s original quantum expression E=hν.
The new definition of the kilogram will be based on the fixed value of the Planck constant, which has been determined with extraordinary precision using Kibble balances and measurements of the mass of silicon atoms. The value of the Planck constant will be exactly 6.62607015 × 10^-34 kg⋅m^2/s, with an uncertainty of 10 parts per billion.
The redefinition of the kilogram will have far-reaching implications for science and technology. It will eliminate the need for physical artifacts as the basis for mass measurements and enable more accurate and convenient measurements of mass. The new definition will also facilitate the development of quantum technologies and improve the accuracy of measurements in fields such as physics, chemistry, and engineering.
The implementation of the new definition of the kilogram will be gradual, with the SI units remaining in effect until the new definition is fully adopted. The change will be particularly significant for the kilogram, as it will be the first SI unit to be redefined in terms of a fundamental constant of nature.
Source: https://www.nist.gov/si-redefinition/kilogram-mass-and-plancks-constant
Keywords: Planck constant, quantized, mass-energy equivalence, Kibble balance, electric kilogram
