Comment Proposed redefinition of SI base units

1 comment

1.1 explicit-unit , explicit-constant definitions
1.2 mass , avogadro constant
1.3 temperature
1.4 luminous intensity

comment

in 2010 marcus foster of commonwealth scientific , industrial research organisation published wide-ranging critique of si in raised numerous issues ranging basic issues such absence of symbol Ω western keyboards abstract issues such inadequate formalism in metrological concepts on si based. changes proposed in new si addressed issues regarding definition of base units including new definitions of candela , mole—units foster argued not true base units. other issues raised foster fell outside scope of proposal.

explicit-unit , explicit-constant definitions

concerns have been expressed use of explicit-constant definitions of unit being defined not related example of quantity have many adverse effects. although criticism applies proposed linking of kilogram planck constant via route requires knowledge of both special relativity , quantum mechanics, not apply proposed definition of ampere, closer example of quantity current definition. observers have welcomed proposal base definition of electric current on charge of electron rather current definition of force between 2 parallel current-carrying wires – since nature of electromagnetic interaction between 2 bodies @ quantum electrodynamics level different nature @ classical electrodynamic levels, considered inappropriate use classical electrodynamics define quantities exist @ quantum electrodynamic levels.

mass , avogadro constant

when scale of divergence between ipk , national kilogram prototypes reported in 2005, debate arose on how best redefine kilogram – should kilogram defined in terms of mass of silicon-28 atom or should determined using watt balance? mass of silicon atom determined using avogadro project , using avogadro s number linked directly kilogram.

concern has been expressed authors of proposal had failed address impact of breaking link between mole, kilogram, dalton (da), avogadro constant (na) , avogadro s number (nn). direct link has caused many argue mole not true physical unit, but, in words of swedish philosopher johansson, mole scaling factor .

the si brochure (8th edition) implicitly defines dalton 0.001÷nn kg value of nn determined experiment. proposal fixes na, if avogadro constant , avogadro s number numerically identical, dalton must related either mass of single carbon atom or kilogram—it cannot related both.

temperature

temperature of enigma – room temperature can measured means of expansion , contraction of liquid in thermometer, high temperatures associated colour. wojciech t. chyla, approaching structure of si philosophical point of view in journal of polish physical society, argued temperature not real base unit rather average of thermal energies of individual particles make body concerned. noted in many theoretical papers, temperature represented quantities Θ or β where

Θ
=

k

b


t
;
 
 
 
β
=


1


k

b


t





{\displaystyle \theta =k_{\text{b}}t;\ \ \ \beta ={1 \over k_{\text{b}}t}}

and kb boltzmann constant.

chyla acknowledged in macroscopic world temperature plays role of base unit of theory of thermodynamics based on temperature. foster, writing point of view of quality control argued introduction of boltzmann constant definition of temperature unnecessary complication.

the consultative committee thermometry, part of international committee weights , measures publishes mise en pratique (practical technique), last updated in 1990, measuring temperature which, @ low , @ high temperatures, makes great use of linking energy temperature via boltzmann constant.

luminous intensity

foster argued luminous intensity [the candela] not physical quantity, photobiological quantity exists in human perception , thereby questioning whether candela should base unit.

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