4 December 2025

9:00 AM – 9:15 AM

Amphi Grand Kursaal

Gaetano Mileti

Gaetano Mileti graduated in physics from the EPFL (Ecole Polytechnique Fédérale de Lausanne, Switzerland) in 1990 and obtained his PhD from the University of Neuchâtel in 1995. He then spent two years at the National Institute of Standards and Technology (NIST) in Boulder (USA) as a guest researcher. Returning to the Cantonal Observatory of Neuchâtel, he set up his own research group in 2001. Co-founder of the Time-Frequency Laboratory (LTF) in 2007, he is a professor of physics at the University of Neuchâtel. His research focuses on atomic spectroscopy, stabilized lasers, and frequency standards. He has participated in the development of rubidium clocks for space applications (used, for example, in the European satellite positioning and navigation system Galileo) and industrial applications, and in the creation of the Swiss primary standard. He is an advisor to the European Space Agency within the GSAC (Global Navigation Satellite System Science Advisory Committee) and a member of the Task Force on the redefinition of the second within the BIPM (International Bureau of Weights and Measures).

What time will it be?

Clocks have taken many forms over the centuries. Based on mechanisms that are sometimes very different, their accuracy has continued to improve as our knowledge and expertise have advanced. The very definition of the exact time has evolved. Like calendars, it has been the subject of numerous negotiations, which are still ongoing today. Until 1967, reference phenomena were governed by the laws of “classical” mechanics: the rotation of the Earth on its axis, or the rotation of the Earth around the Sun. The instruments used to measure this time were telescopes pointing at distant celestial objects. It can be said that the exact time was defined by the infinitely large. It was “starlight time.” Then the reference changed, as did the phenomena and physical laws that describe them. The atom has, in a sense, replaced the Earth, while “quantum” mechanics has emerged as the theoretical framework. New limits of stability were thus reached in the measurement of time. Its fundamental unit, the second, was even redefined. The exact time became the time of the infinitely small, the “time of atoms” of cesium. But its days may be numbered…