Speaker
Dr
Waldemar Nawrocki
(Poznan University of Technology, Poznan, Poland)
Description
The possibility or even necessity of revising definitions of some of the base units of the present SI has been discussed over the past 25 years. Taking advantage of recent achievements of physical science it is possible to construct quantum standards of units which use fundamental physical constants or atomic constants.
The last 25th General Conference of Weights and Measures (2014) expressed their intention to accept the new system of units in next future. In the system of units four basic units will be new defined: the kilogram (on a base of the Planck constant, h), the ampere (by the elementary charge, e), the kelvin (by the Boltzmann constant, kB), and the mole (by the Avogadro constant, NA). The values of this four fundamental physical constants (h, e, kB and NA) will be fixed as known exactly.
The new SI system will be proposed if new definitions will be ready for all four base units. The new definition of the kilogram, based on the Planck constant, h, is crucial. Therefore, in 2010 the Consultative Committee for Mass set out three requirements (confirmed in February 2013), concerning uncertainty in determination of h, which should be fulfilled before the ICPM will to an official proposal to the CGPM conference. Requirements on determination of the Planck constant, h:
- At least three independent results (watt balance and XRCD) with relative uncertainty ur < 5 × 10-8.
- At least one result with relative uncertainty ur ≤ 2 × 10-8 ;
- Results consistent.
These requirements are not fulfilled up today. The next chance to accept the new system of units will be in 2018, at 26th CGPM conference.
Author
Dr
Waldemar Nawrocki
(Poznan University of Technology, Poznan, Poland)
