SI units are now defined directly in terms of physical laws (no prototypes needed). https://en.wikipedia.org/wiki/2019_redefinition_of_the_SI_base_units https:

SI units are now defined directly in terms of physical laws (no prototypes needed). https://en.wikipedia.org/wiki/2019_redefinition_of_the_SI_base_units https://en.wikipedia.org/wiki/2019_redefinition_of_the_SI_ba...