The Quantum SI - Towards the New Systems of Units

Abstract

The possibility or even necessity of revising definitions of some of the base units of the present SI has been discussed over the past 15 years. The last General Conference of Weights and Measures (2007) recommended to redefine the kilogram, the ampere, the kelvin, and the mole using fixed values of the fundamental constants by the time of the next General Conference in 2011. This paper is a review of proposals of new definitions of units of mentioned quantities and arguments voting for particular variants of definitions. Most relevant papers for this review have been published by Metrologia, the international journal appointed at the BIPM, and many other useful pieces of information are available on www pages of the BIPM. The author notes that not only new definitions have been discussed but as well as the set of the base units of the SI. It means a replacement of the ampere by the volt or the kelvin by the joule. Decisions concerning new definitions are not made and the discussions are still open.

Toward improved understanding of the physical meaning of entropy in classical thermodynamics

“…The argument for this change is that precise temperature measurement based on the kelvin is still dependent on the equilibrium properties of some chosen material, whereas relating temperature to the more uuniversal constant, k B , will make temperature measurement independent of the material, method of realization, and temperature range. Another area where the need to emphasize energy unit over the kelvin is in quantum metrology, where the authors argue that the necessary conditions of thermodynamic equilibrium and thermal contact are not made, thus making meaningless energy quantification through the kelvin [18,19]. These issues are related to entropy definition in the sense that entropy definition was seen as a basis for the realization of a thermodynamic temperature scale.…”

Toward Improved Understanding of the Physical Meaning of Entropy in Classical Thermodynamics

“…Could some of these conceptual problems be resolved by only including energy variables in entropy definition and dispensing with the central role of temperature? Furthermore, in quantum metrology, some authors argue that the conditions for thermodynamic equilibrium and thermal contact are not met; this renders energy quantification through the kelvin meaningless [18,19]. These issues are all related to entropy definition in the sense that its definition was seen as a basis for the realization of a thermodynamic temperature scale.…”