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Cake day: June 4th, 2025

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  • …The Planck constant is a set distance. It’s being used here to define other things as a constant. The very article on the kilogram states outright that SI units’ foundation is three constants: “a specific transition frequency of the caesium-133 atom, the speed of light, and the Planck constant.”

    Vacuum permeability is how much electric currents affect magnetic fields in a vacuum. As in, when there are no other interferences. It is not variable. The speed of light when there is no interference is not ‘affected by’ vacuum permability any more than a cartesian graph is ‘affected by’ the set of real numbers. Vacuum permeability describes vacuum, it doesn’t define it. Same goes for permittivity.

    You ARE correct about the kilogram no longer being a number of specific atoms, though.


  • The two constants - the speed at which light moves, and the unperturbed ground-state hyperfine transition frequency of cesium - can be combined to define every measurement of time, length, and velocity. They are the constants by which everything else is defined.

    Throw in mass, which is easy - a certain number of atoms of a specific element will also have a universally constant mass. Combine it with the other two constants and you have force, energy, and work, and voila, you can describe nearly everything in classic physics.