Jean-Luc Lehners (born 1978 in Luxembourg) studied physics and mathematics at Imperial College London and at the University of Cambridge. He obtained his Ph.D. in 2005 at Imperial College for his research on braneworlds in supergravity.
After holding postdoctoral positions at the University of Cambridge, Princeton University (USA) and the Perimeter Institute (Canada), he established the Theoretical Cosmology group at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute) in Potsdam in 2010. Dr. Lehners is the recipient of both an ERC Starting Grant (2010) and a Consolidator Grant (2017). He works on early universe cosmology, with a particular emphasis on the big bang as well as on quantum e ects in cosmology.
The prevailing theory for the origin of all structures in the universe is that they arose out of ampli ed quantum perturbations in the early universe. Beyond this crucial use of quantum theory, it seems clear that if we want to understand the big bang, and the beginning of space and time, we will need to apply quantum theory to the entire universe. We can make progress on this front by applying semi-classical path integral techniques to gravity. In the presence of gravity, there were however long-standing complications such as the conformal mode problem. We will
explain how a key development, namely the use of Picard-Lefschetz theory, allows us to overcome these di culties, and allows us to assess theories of the initial conditions of the universe such as the no-boundary proposal of Hartle and Hawking. The gravitational path integral also hints at the existence of quantum transitions across the big bang, into an earlier phase of cosmological evolution.