Why is the kilogram a base unit in SI instead of the joule? The kilogram is the only base unit still defined from an artifact. Since the artifact can change with time and the kilogram has been know to do so, wouldn't it be better if a different unit were to replace the kilogram as a base unit?
Energy is the most fundamental substance in nature. Energy has always existed, even before the universe was created and will exist long after the universe is gone. Energy is universal. Wouldn't it be simpler to define one joule of energy from basic principles in physics and define the kilogram from the joule in the relationship that 1 kg = 1 J s**2/m**2? Or, the kilogram can be defined from the newton, the meter and the second, which are already accurately defined. The ampere also should not be a base unit, the coulomb should be. Since the ampere is defined from the newton and the newton is defined from the kilogram, then the practical realization of the ampere is affected when the kilogram changes. >From the Wikipedia article on the coulomb: In principle, the coulomb could be defined in terms of the charge of an electron or elementary charge. Since the values of the Josephson (CIPM (1988) Recommendation 1, PV 56; 19) and von Klitzing (CIPM (1988), Recommendation 2, PV 56; 20) constants have been given conventional values (KJ ≡ 4.835 979 × 1014 Hz/V and RK ≡ 2.581 280 7 × 104 Ω), it is possible to combine these values to form an alternative (not yet official) definition of the coulomb. A coulomb is then equal to exactly 6.241 509 629 152 65 × 1018 elementary charges. Combined with the present definition of the ampere, this proposed definition would make the kilogram a derived unit. The ampere can then become a derived unit (1 A = 1 C/s) that is very accurately defined since the coulomb and the second are accurately defined. The newton would be defined as: 1 N = 1 J/m.s; if the joule is base unit defined from some principle of physics. The kilogram would then be defined from the newton as 1 kg = 1 N s**2/m**2. Otherwise, the newton would have to be a base unit and defined from the same rule that defines the ampere, but in reverse. Either way, this would eliminate the kilogram being tied to an artifact. Simon
