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SYDK: Symposium Quantum Mechanics and Gravity: Current Status

SYDK 1: Quantum Mechanics and Gravity: Current Status

SYDK 1.3: Invited Talk

Thursday, April 3, 2025, 11:45–12:15, ZHG008

Causal Dynamical Triangulations: Lattice quantum gravity reloaded — •Renate Loll — Radboud University, Nijmegen, The Netherlands

Lattice methods are a powerful tool to investigate quantum field theories beyond perturbation theory, as demonstrated by the impressive successes of lattice QCD. Due to the dynamical character of spacetime in gravity, putting quantum gravity on the lattice faces formidable obstacles, which for a long time were thought to be insurmountable. Key to overcoming them is to adapt the lattice regularization such that both the dynamical and the Lorentzian character of spacetime are built in from the outset. This is realized by the use of causal dynamical triangulations (CDT), which capture the inherent compatibility between the principles of quantum theory and general relativity.

Lattice quantum gravity based on CDT is well-tested and operational, using state-of-the-art Monte Carlo simulations. It has opened a computational window near the Planck scale, where “numerical experiments” can be performed, giving for the first time quantitative information on the spectra of geometric observables characterizing quantum gravity nonperturbatively, with unexpected results. Remarkably, a quantum spacetime has been shown to emerge from this primordial soup of quantum fluctuations, displaying large-scale properties of a de Sitter universe. There is a concrete and promising roadmap, focusing on the properties of these quantum fluctuations, to connect fundamental quantum gravity to early-universe cosmology.

Keywords: quantum gravity; lattice gravity; nonperturbative path integral; quantum spacetime