Why are the kilogram, ampere, kelvin, and mole still considered base units and not derived? Given their current definitions, they're purely defined in terms of other units and cannot be independently measured, right?
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Well, Kelvin is based on a known (if theoretical) value, absolute zero. And it is the same size per unit as Celsius. So I’d say that’s independently understood. Kilos are directly mapped to litres (1 litre of water weighs 1 kilo), but yeah, it’s strange that’s the base.
Right, those are the historical definitions. But today the kg is defined in terms of the Planck constant, and Kelvin in terms of the Boltzmann constant.
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You are way over my head with that.
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https://en.wikipedia.org/wiki/2019_redefinition_of_the_SI_base_units … Either way until last year, the formal definition of the kg had been the mass of a block of metal in France since the 1800s. Not sure about the history of the Kelvin
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