The ampere is still a base unit, according to the SI brochure. However, in my perception the recent redefinition of units effectively defines the Coulomb as e/(1.602 176 634 × 10^−19), and the ampere is derived as 1 A = 1 C/s. Why did they not make the coulomb a base unit, instead of the ampere, last year?
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It appears that they have deemphasized the concept of "base units". They did not remove the term, but mention that all units are now defined in terms of constants. As wikipedia puts it:
With the 2019 redefinition, the SI is constructed around seven defining constants, allowing all units to be constructed directly from these constants. The designation of base units is retained but is no longer essential to define SI measures.
From the 9th edition of the SI Brochure
The choice of the base units was never unique, but grew historically and became familiar to users of the SI. This description in terms of base and derived units is maintained in the present definition of the SI, but has been reformulated as a consequence of adoption of the defining constants.
With that position, there seems to be no strong desire to modify which units comprise the set of base units.
BowlOfRed
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It's also important to add, that it's hard to change.. All the textbooks and education. If it was easy, then for better consistency they would apply the metric system in the US too. It could be hard for many, many wouldn't care or wouldn't understand why!
Kregnach
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The redefinition of the SI was to untangle all the different units from each other, and have nature constants for basis(so no lumps of metal anymore).
And ampere has a good definition, so why change that? It is not going to change, like the other elements, and if the natural constants are meta-stable, we have bigger things to worry about than some measurements.
Dr_Bunsen
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