  We study gravity coupled to a scalar field in spherical symmetry using loop
quantum gravity techniques. Since this model has local degrees of freedom, one
has to face ``the problem of dynamics'', that is, diffeomorphism and
Hamiltonian constraints that do not form a Lie algebra. We tackle the problem
using the ``uniform discretization'' technique. We study the expectation value
of the master constraint and argue that among the states that minimize the
master constraint is one that incorporates the usual Fock vacuum for the matter
content of the theory.
