Localised particles and fuzzy horizons: a tool for probing quantum black holes

The horizon is a classical concept that arises in general relativity and is therefore not clearly defined when the source cannot be reliably described by classical physics. To any (sufficiently) localised quantum mechanical wavefunction, one can associate a horizon wavefunction which yields the probability of finding a horizon of given radius centred around the source. We can then associate to each quantum particle a probability that it is a black hole, and the existence of a minimum black hole mass follows naturally, which agrees with the one obtained from the hoop conjecture and the Heisenberg uncertainty principle.