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AGPhil: Arbeitsgruppe Philosophie der Physik

AGPhil 15: Quantum Gravity 3

AGPhil 15.3: Vortrag

Donnerstag, 21. März 2024, 16:00–16:30, PTB SR AvHB

An effective approach to quantum gravity : the pragmatic solution we never dreamt of, but already have — •Etienne Ligout — Institut d'Histoire et de Philosophie des Sciences, Paris, France

Upon quantization, general relativity proves to be unrenormalizable: the perturbative expansion breaks down at the Planck scale. Most of the efforts to devise a coherent quantum theory of gravitation have thus historically been focused on finding an ultraviolet completion of general relativity up to the Planck scale. In this talk, I shall argue that this endeavour - while relevant to tackle some limitations of the classical framework (such as singularities) - is not warranted from an empirical standpoint, simply because we are far from being able to probe the Planck scale. In fact, at all the scales currently accessible, the quantum corrections to the gravitational dynamics remain small, and - crucially - can be computed. This is achieved by adopting an effective approach, where only the dominant contributions in the action (at the energy scale considered) are retained. When carried out, this program yields a comprehensive quantum gravity theory at low energies, giving for instance the quantum corrections to the newtonian potential or to the bending of light around a star (see e.g. Donoghue 1994). Building on these results, I defend a pragmatic approach to the problem of quantum gravity : rather than wonder what happens to gravity at the Planck scale in spite of any empirical support, we should adopt an effective point of view and restrict our focus to energy regimes where the quantum gravitational effects are well controlled and understood.

Keywords: quantum gravity; effective field theory; quantum corrections