  In the lack of a full-fledged theory of quantum gravity, I consider free,
scalar, quantum fields on curved spacetimes to gain insight into the
interaction between quantum and gravitational phenomena. I employ the
Unruh-DeWitt detector approach to probe thermal, quantum effects on static,
non-globally hyperbolic spacetimes. In this context, all physical observables
depend on the choice of a boundary condition that cannot be singled-out, in
general, without resorting to an experiment. Notwithstanding, the framework
applied admits a large family of (Robin) boundary conditions and grants us
physically-sensible dynamics and two-point functions of local Hadamard form. I
discover that the anti-Unruh/Hawking effects are not manifest for thermal
states on the BTZ black hole, nor on massless topological black holes of four
dimensions. Whilst the physical significance of these statistical effects
remains puzzling, my work corroborates their non-trivial relation with the KMS
condition and reveals the pivotal influence of the spacetime dimension in their
manifestation. On global monopoles, I find that for massless minimally coupled
fields the transition rate, the thermal fluctuations and the energy density
remain finite at the singularity only for Dirichlet boundary condition. For
conformally coupled fields, although the energy density diverges for all
boundary conditions, the transition rate and the thermal fluctuations vanish at
the monopole; indicating that even if there is infinite energy, no spontaneous
emission occur if the quantum field is not fluctuating. Moreover, I explicitly
construct two-point functions for ground and thermal states on Lifshitz
topological black holes, setting the ground for future explorations in this
Lorentz breaking context.
