The road to quantum gravity: from elementary considerations to universal predictions

General relativity and quantum theory are two cornerstones of modern physics, which, despite their huge individual successes, have so far failed to work together in a complete and consistent way. As a consequence, the unification of the two theories in a consistent formulation of quantum field theory on curved spacetimes and eventually in a theory of quantum gravity has become one of the holy grails of modern physics. In this thesis, some of the many aspects of such a theory of quantum gravity are explored. The first part of the thesis is devoted to the construction of diffeomorphism invariant theories on a spacetime that is itself uctuating. We show how this can be achieved for basic theories using second order geometry, which is an extension of the geometrical framework applied in general relativity. After these elementary considerations, we move on to study predictions from quantum gravity at sub-Planckian energy scales, where quantum field theory and general relativity can be combined in the framework of effective field theory. The resulting effective field theory of gravity allows to make model independent predictions in quantum gravity. In the second part of the thesis, we discuss perturbative predictions following from the unique effective action for quantum gravity. Here, we particularly focus on predictions from this formalism for compact stars, black holes and the fate of singularities in quantum gravity. Finally, in the third part, we use effective field theory and the universality of the gravitational coupling to study quantum gravitational effects that lie within the reach of current experiments. We then discuss the implications for beyond the Standard Model physics and dark matter models in particular.