The changing role of base units within the revised SI: an opportunity to take dimensional analysis back to its roots

Abstract

The role of base units, base quantities and dimensions in the proposed revision of the SI is discussed. Although the primary role of the seven current base units would be lost when the SI is fixed by seven defining constants, we suggest that there would still be seven base units, but with some flexibility in how they are selected. We agree with the proposal that the current set of seven SI base quantities and associated units should retain special status, but point out that this would become a convention and would not be a direct consequence of the set of defined constants. Although dimensional analysis is currently described within the SI brochure as directly linked to the SI base units, we suggest that this is not necessary and that the flexibility introduced by the revised SI should be seen as an opportunity to allow different sets of dimensions to be chosen in different circumstances. This would bring dimensional analysis closer to its original form.