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?
> not some kind of fundamental value. This just makes the base/derived split weird though. The name implies (and it used to mean AFAIK) a unit that was fundamentally required to describe the universe. If its definition is in entirely terms of other units, that's not the case
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Granted I also don't fully understand how the modern definition of the kg even works since it seems like it defines it in terms of the mass of a photon but photons have no mass so ¯\_(ツ)_/¯
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It has energy so it's just E = mc2 I guess? Just glad it's above my pay grade to think about these things

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