Understanding the quantum nature of space-time is an open challenge both from a theoretical and an experimental point of view. Quantum gravity effects are crucial, for example, in gravitational collapse of astrophysical objects, in understanding the inner working of black holes and Hawking thermodynamics as well as in the evaporation process of Planck-size black holes. Once the form of the quantum corrections for black hole physics is known, it can be studied via gravity wave observatories and black hole imaging techniques. Rather than speculating on the noble endeavour of an ultimate nature of quantum gravity, I believe that it is more impactful to construct effective frameworks allowing to parametrise quantum corrections to Einstein’s theory of general relativity to extract reliable predictions (see https://journals.aps.org/prd/pdf/10.1103/PhysRevD.106.046006).

In our recent work https://arxiv.org/pdf/2305.12965.pdf we analyse the impact of positivity conditions (sometime known also as energy conditions) on static spherically symmetric deformations of the Schwarzschild space-time. The metric is taken to satisfy, at least asymp-
totically, the Einstein equation in the presence of a non-trivial stress-energy tensor, on which we impose various physicality conditions. We systematically study and compare the impact of these conditions on the space-time deformations. It is extremely exciting that the universal nature of our findings applies to both classical and quantum metric deformations with and without event horizons. The conditions have immediate impact on known models of quantum black holes and the construction of future ones.