A practitioner's view on quantum gravity

Quantum gravity is a subject difficult to grasp for outsiders. Which lofty ideas of exotic structures at the Planck scale will turn out to be right? Do theorists agree on what ''quantum gravity'' means and what questions such a theory should answer? How far are we from obtaining answers? My collaborators and I show by explicit construction that understanding nonperturbative quantum gravity does not require hitherto unseen symmetries, dimensions, strings, loops or branes, which appear to lead us ever further away from a unique theory. Staying within the framework of quantum field theory, but adapting it to the situation where spacetime itself is dynamical, Quantum Gravity from Causal Dynamical Triangulations (CDT) is a promising candidate theory of this type. It is a gravitational analogue of obtaining nonperturbative QCD as the scaling limit of a lattice theory, and is unique in producing evidence of a good semiclassical limit. Not only may this approach lead us to the correct theory of quantum gravity, it also provides a concrete and extremely useful computational framework to study fundamental questions. One example is the recent demonstration that a renormalization group analysis can be set up and performed in CDT quantum gravity despite its background-free character.