Probing the quantum nature of gravity at all scales

To understand the quantum structure of spacetime, we must confront proposed theories of quantum gravity with experimental data.

This is a challenge, because quantum-gravity effects are generally assumed to manifest at the Planck length, which lies far beyond current experimental reach. I challenge this assumption by probing quantum gravity at different scales.

To achieve this, I propose to use lever arms that translate predictions of quantum gravity at the Planck scale into predictions at larger distances, where we can compare them to experimental data. I have identified such lever arms in particle physics, black holes and cosmology.

The proposals first testing ground for quantum gravity is particle physics, where the scale dependence of couplings is a lever arm that translates Planck-scale predictions into testable predictions at larger distances. Using this lever arm, I will predict the values of couplings in the Standard Model and models of dark matter.

The second testing ground is black holes, where the spin can act as a lever arm that translates Planckian physics into horizon-scale effects. To use this lever arm, I will derive spinning black-hole spacetimes and explore their image features.

The third testing ground is late-time cosmology, where the dark energy is a lever arm that translates a microscopic interplay of scalar fields with gravity into an accelerated expansion of the universe.

To use this lever arm, I will predict the properties of dark energy.The proposals main objective to confront quantum gravity theory with observational data will thus be achieved by forging new connections between quantum gravity and other research fields.

These novel connections also provide a fresh perspective on long-standing questions in these other fields, for example on the nature of dark matter and dark energy.

To demonstrate the power of these lever arms, I will work in the framework of asymptotic safety, a compelling framework for a quantum theory of gravity.