Jo E. Wolff (King's College London)
Changing the definitions of SI units changes what can be known empirically and what is fixed by definition. In this talk I address whether we have reason to be concerned about removing the numerical value of fundamental constants like Planck's constant and the speed of light in vacuum from empirical determination. I do so by comparing definitions in terms of fundamental constants with definitions in terms of prototypes (as in the case of the old definition of the kilogram) and definitions in terms of non-fundamental constants (as in the case of the mole).
