Question

From the "no hair theorem" we know that black holes have only 3 characteristic external observables, mass, electric charge and angular momentum (except the possible exceptions in the higher dimensional theories). These make them very similar to elementary particles. One question naively comes to mind. Is it possible that elementary particles are ultimate nuggets of the final stages of black holes after emitting all the Hawking radiation it could?

Answer 1

This is indeed a tempting suggestion (see also this paper). However, there is a crucial difference between elementary particles and macroscopic black holes: the latter are described, to a good approximation, by non-quantum (aka classical) physics, while elementary particles are described by quantum physics. The reason for this is simple.

If the classical radius of an object is larger than its Compton wavelength, then a classical description is sufficient. For black holes whose Schwarzschild radius is bigger than the Planck length this is fulfilled. However, for elementary particles this is not fulfilled (e.g. for an electron the "radius" would refer to the classical electron radius, which is about cm, whereas its Compton wavelength is about three orders of magnitude larger).

Near the Planck scale your intuition is probably correct, and there is no fundamental difference between black holes and elementary particles - both could be described by certain string excitations