18 November 2023

14:00 – 14:45

Amphithéâtre Painlevé

Bruno Mansoulié

Bruno Mansoulié is a physicist at CEA, in the particle physics department, which he headed for 5 years. He has contributed to several major discoveries in the field, including the W and Z particles at CERN in 1984, the quark top at Fermilab (USA) in 1995, and the famous Higgs boson, at CERN in 2012. From the outset (1992), he has been a member of the international ATLAS collaboration, which built one of the two huge detectors at the LHC, CERN’s large proton collider. After the start-up of the LHC in 2008, he was part of the data analysis team searching for the Higgs boson. After its discovery in 2012 by the ATLAS and CMS collaborations, he led the ATLAS teams that expanded and crossed measurements on this new particle, enabling precise comparisons with theory. For this work, he was awarded the Prix Charpak-Ritz 2023 by the Société Française de Physique and the Société Suisse de Physique. Bruno Mansoulié is committed to the dissemination and questioning of science, and has given numerous open lectures and published two books for the general public.

Conference: What is vacuum energy?

Our universe is expanding, and this expansion is accelerating. According to the theory of general relativity, this acceleration is due to a parameter that can be interpreted as the energy of the cosmic vacuum. Thanks to the observations of the last few decades, the value of this parameter is now known with good precision. For quantum theory, which claims to understand the elementary fields and particles present in the universe, the energy of the vacuum is an ill-defined concept that should not be involved in calculations, where it plays no more than a background role. Yet the confrontation of these two visions leads to one of the most important problems in fundamental physics. In this lecture, I’ll try to describe in simple words the two theoretical visions, where the problem lies, and why it’s impossible to ignore it today.