SI Base Units & Constants

I recently stumbled upon a well-written (but outdated) overview of the base SI units from Theodore Wildi's Electrical Machine Drives and Power Systems.

I heard about the 2019 changes to these definitions, but I totally missed the elegance of the new model:

Dependence of base unit definitions on physical constants with fixed numerical values and on other base units that are derived from the same set of constants.

Each of our SI units now roughly derives from a fundamental constant! Neat!

Apparently the definition of "fundamental constant" is itself a bit wishy-washy, but Uzan's summary seems tidy:

• the gravitational constant G
• the speed of light c
• the Planck constant h
• the 9 Yukawa couplings for the quarks and leptons (equivalent to specifying the rest mass of these elementary particles)
• 2 parameters of the Higgs field potential
• 4 parameters for the quark mixing matrix
• 3 coupling constants for the gauge groups > SU(3) × SU(2) × U(1) (or equivalently, two coupling constants and the Weinberg angle)
• a phase for the quantum chromodynamics vacuum

Anyway, I love this universe: