4 December 2025

9:50 AM – 10:35 AM

Amphi Petit Kursaal

François Vernotte

François Vernotte is Professor Emeritus of Astronomy and Astrophysics at Marie & Louis Pasteur University. At OSU THETA (Besançon Observatory) and FEMTO-ST (Besançon), he has devoted his career to measuring the temporal stability of oscillators, whether atomic standards (cesium jet clocks, hydrogen masers) or astronomical oscillators such as millisecond pulsars. He is the author of some fifty scientific publications and co-author, with Sarah Carvallo and Clément Lacroute, of an interdisciplinary book currently in press: À la recherche du Temps Universel (In Search of Universal Time).

Measuring time: how far will the quest for precision go?

Time structures life, yet it is a very difficult concept to define: it passes inexorably, always in the same direction… While questioning its nature, humanity has sought to measure time since prehistoric times. Today, for physicists, time remains a special, even strange dimension of Einstein’s space-time; but it is also the physical quantity that we measure with the lowest uncertainty: ±1 × 10^-18 (1 +/- 0,000000000000000001). However, far from being a curiosity of interest only to a few scholars, the applications of this extreme precision affect us every day (telecommunications, GPS, etc.) and push us to go ever further. Is there an ultimate limit to this irrepressible thirst for precision, a limit that is due to the very nature of time?