Sigma Club Seminar by Francesca Vidotto (Instituto de Estructura de la Materia (IEM - CSIC))

Title: Philosophy of Quantum Gravity

Abstract: Quantum gravity is often said to make spacetime “disappear”, raising worries about empirical coherence: if there is no space and time at the fundamental level, what are our observations about? I will argue that much of this worry comes from running together distinct notions of space and time. The relational notion (contiguity between physical entities, succession between events) survives in Loop Quantum Gravity. The quanta of the gravitational field are not located in space; with their adjacency relations, they make up a relational space. What emerges, in a weak and standard sense of approximation, is the Newtonian “container” and the continuous metric manifold of General Relativity. I will then turn to observability and the status of the theory’s discrete structures. Placing the Heisenberg cut on the boundary of a spacetime region lets the theory make predictions from partial observables, without explicit Dirac observables. These predictions are computed on finite graphs and two-complexes. I will argue that this truncation is not a defect: any measurement captures finitely many degrees of freedom, just as lattice QCD and perturbative QFT always work on finite structures. Finally, I will separate three notions of time and argue that the “problem of time” dissolves once dynamical evolution is distinguished from experienced flow.

Reference: C. Rovelli and F. Vidotto, "Philosophical Foundations of Loop Quantum Gravity", in the "Handbook of Quantum Gravity", 2023, Springer.

Francesca Vidotto is a Tenured Research Scientist at the Instituto de Estructura de la Materia of the Spanish National Research Council (IEM-CSIC) in Madrid. She works on the quantum properties of space and time, on topics ranging from cosmology to quantum information. She trained in theoretical physics at the Universities of Padua and Pavia and pursued research in quantum gravity in France, the Netherlands and Spain. From 2019 to 2025 she held a Canada Research Chair in the Foundations of Physics at Western University, where she was Associate Professor of Physics and Astronomy and of Philosophy, and Associate Director of the Rotman Institute of Philosophy. She currently teaches philosophy of physics at the Università della Svizzera italiana in Lugano. She is committed to increasing the presence of women and underrepresented groups in research, to science communication that is both poetic and rigorous, and to science as an instrument of peace and democracy.

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