How do you measure a planet? In 1792, two French astronomers set out to do just that—laying the foundation for a new, universal system of measurement that would forever change science, society and international cooperation.

At the BIPM–UNESCO World Metrology Day Symposium, held during the 150th Anniversary of the Metre Convention, Professor Ken Alder, Professor of History at Northwestern University, USA and author of 'The Measure of All Things', delivered a keynote address on tracing the radical ideals behind the original metric system—and how they evolved into today’s global metrology framework.
 

Watch our interview

In this short video, Prof. Alder speaks with the BIPM about the creation of the metric system during the French Revolution—why something so often taken for granted was, in fact, the product of immense scientific effort and political ambition.

[1 minute 39 seconds]

Watch Ken Alder's Keynote Address

Watch Prof. Alder’s keynote address at #BIPM150, as he recounts how the metre emerged from revolutionary ambitions and universal ideals—through the Delambre–Méchain meridian expedition—and how debate, consensus and international conventions made those standards endure.

He also shows how the push for precision led to new tools like least-squares, linking scientific innovation to the cooperative spirit behind the Metre Convention.

[37 minutes]

This article is part of a 14-part feature series highlighting some of our keynote speakers at the 150th Anniversary of the Metre Convention. See our dedicated YouTube playlist for the full list of interviews (to-date), with new features and videos being published periodically until December 2025.