40 years of Classical and Quantum Gravity

Abstract

This year we celebrate 40 years since IOP Publishing launched its then newest journal Classical and Quantum Gravity (CQG). Looking back, 1984 was a quiet but steady time for gravitational research, but in the intervening four decades this field has blossomed with the direct detection of gravitational waves in 2015 and enjoyed steady growth and diversification since that Nobel Prize-winning breakthrough discovery. CQG has played a leading role throughout this journey, covering all aspects of gravitational research, both classical and quantum, and including mathematical, numerical, theoretical, observational and experimental investigations.Mathematical relativity was a key area in the early years and remains a pillar of the journal: 'Classical double copy at null infinity' (2022) [1], 'Smooth Gowdy-symmetric generalised Taub-NUT solutions with polynomial initial data' (2024) [2], 'Focus on Asymptotic Symmetries, Conserved Quantities, and Flat Space Holography ' [3]. Numerical relativity is a core element of the gravitational wave detection program, and recent years have seen a surge in papers producing refined numerical solutions to the problem of two black holes and/or neutron stars orbiting each other, and more accurate predictions of the waveforms produced by the gravitational radiation emitted by these systems: topical review 'Lessons for adaptive mesh refinement in numerical relativity' (2022) [4], 'A higher-multipole gravitational waveform model for an eccentric binary black holes based on the effective-one-body-numerical-relativity formalism' (2022) [5], 'Second release of the CoRe database of binary neutron star merger waveforms' (2023) [6].Black holes are central to modern gravity, and theoretical studies of their properties are an important focus of CQG: 'Shadow and deflection angle of charged rotating black hole surrounded by perfect fluid dark matter' (2022) [7], 'Restricted phase space thermodynamics for AdS black holes via holography' (2022) [8], 'Energy scales and black hole pseudospectra: the structural role of the scalar product' (2022) [9]. Recent experiments, including measurements of gravity on microscopic levels, are edging us closer towards formulating a theory of quantum gravity, and research in this area is gathering pace: 'Focus Issue on Numerical Investigations in Non-Perturbative Quantum Gravity' [10], 'Focus on Quantum Gravity Phenomenology in the Multi-Messenger Era: Challenges and Perspectives ' [11], 'Unitarity, clock dependence and quantum recollapse in quantum cosmology' (2022) [12].With the advent of precision cosmology in recent years, it is now possible to probe gravitational physics at cosmic scales with unprecedented accuracy, thereby powering our comprehension of the intricate relationship between gravity and the cosmos: 'Is the observable Universe consistent with the cosmological principle?' (2023) [13], topical review 'Observations in quantum cosmology' (2023) [14], 'Focus Issue on the Hubble Constant