Defining and Redefining the International System of Units

The International System of Units, the SI, is the common basis for all of the world's measurements.  It is at the cutting edge of research and science; it is the enabler of technological interoperability and advancement; and it is the foundation of all industrial networks and their economic impacts.  To some these may seem to be extravagant claims but the SI is incredibly pervasive.  It is present in everything from plotting a satellite trajectory to buying a kilo of bananas.

How did all of this come about?  How robust is this measurement system and can we count on it in the future?

I will begin by reviewing the structure and history of the SI, how it was originally developed and how it has grown to encompass all of our physical measurement needs.  I will discuss its limitations and ultimate goals.  Then I will introduce fundamental constants and show how they have slowly become intertwined with the units.

I will describe the proposed changes to the SI which will be based on the exact fixing of  the values of five fundamental constants.  To the end user the structure of this 'new SI' will only undergo a subtle change, but philosophically this will be the most profound change to the SI in over a hundred years.  The new SI will anchor all future measurements onto the most stable and universally accessible 'artefacts' that have ever been discovered.  The change  will also reduce the uncertainties of the values of many other fundamental constants and ensure long term stability of our units of measure.

Finally, I will outline the organizations that will recommend, approve and ultimately implement these changes to the world's measurement system.