Black Holes, Gravitational Waves and Space-Time Singularities Lemaitre Conference 2024

Abstract

This editorial introduces the topical collection arising from the Lemaitre Conference 2024 - the second in a series of meetings dedicated to the scientific legacy of Georges Lemaitre - held at the Vatican Observatory in Castel Gandolfo, 17-20 June 2024, fifty-seven years after Lemaitre's death and on the eve of the centenary of his foundational 1927 paper on the expanding universe. The nineteen contributions collected here address the most pressing open problems at the interface of cosmology, gravitation, and quantum theory: the Hubble tension and the future of $Λ$CDM in light of recent DESI data; inflationary cosmology and dark-energy model-building in string theory and supergravity, together with the Swampland constraints that bound them; the observer-dependence of the quantum-cosmological wave function; the removal, or consistent crossing, of spacetime singularities - from the canonical quantization of Lemaitre's own 1933 dust model to string-theoretic pre-Big-Bang bounces and many-body constructions of singularity-free black-hole cores; primordial black holes and their gravitational-wave signatures; the search for a background-independent formulation of quantum gravity and a first-principles account of horizon thermodynamics; and the foundational status of the quantum-to-classical transition in gravitational contexts. A proposal for lunar-based cosmological observations, and a historical reconstruction of the genesis of Lemaitre's primeval-atom hypothesis, complete the collection. A recurring unifying thread was the legacy of Lemaitre himself - who first distinguished coordinate from physical singularities and coined the term "horizon" - whose pioneering vision continues to guide research at the frontier of cosmology and fundamental physics.