Nearly 130 years after the kilogram was first defined by a lump of metal in a vault in Paris, scientists have voted for change and a new system that redefines the global measure of mass in terms of a fundamental constant of nature. Following a historic vote on Friday at the General Conference on Weights and Measures in Versailles, the kilogram will no longer be defined by the international prototype kilogram (IPK), a platinum alloy cylinder fashioned in 1889, but by Planck’s constant, a number that is deeply rooted in the quantum world. One got a sense of how big metrology is.”

The IPK, or Le Grand K, has served the world well but scientists have long known that even though, by definition, it is precisely one kilogram, its weight changes over time. What Kibble and Robinson realised is that you could balance this magnetic force against a physical mass – a little like resting a mass on your speaker cone and measuring how much electrical current you need to run through your electromagnetic to get it to move. Along with the kilogram, three other base units will be redefined as a result of the vote. The expected new definitions:

The kilogram – will be defined by the Planck constant (h)

– will be defined by the Planck constant (h) The ampere – will be defined by the elementary electrical charge (e)

– will be defined by the elementary electrical charge (e) The kelvin – will be defined by the Boltzmann constant (k)

– will be defined by the Boltzmann constant (k) The mole – will be defined by the Avogadro constant (N A )

Old definitions:

The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram

is the unit of mass; it is equal to the mass of the international prototype of the kilogram The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 m apart in vacuum, would produce between these conductors a force equal to 2 x 10–7 newton per metre of length

is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 m apart in vacuum, would produce between these conductors a force equal to 2 x 10–7 newton per metre of length The kelvin is the unit of thermodynamic temperature, which is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water

is the unit of thermodynamic temperature, which is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12. A replica of the International Prototype Kilogram is pictured is seen at the 26th meeting of the General Conference on Weights and Measures (CGPM) to vote on the redefinition of four base units of the International System of Units (SI) in Versailles, France, November 16, 2018. That physical object is a chunk of metal perpetually housed underground at the "Bureau international des poids et mesures", the International Bureau of Weights and Measures, in Sèvres, France.
A new definition of SI units, e.g., the kilogram, the ampere, etc., is decided by the General Conference on Weights and Measures. They are now entirely defined by physical constants, and no longer dependent on any physical object, as was previously the case for the kilogram.