OBSERVABLES IN QG

Physical Observables in Quantum Gravity

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 Obiettivo del progetto (Objective)

'In recent years a very good understanding of the kinematical structures provided by candidate theories of quantum gravity, such as Loop Quantum Gravity, Spin Foam Models and Causal Dynamical Triangulations, has been obtained. The next key step is to approach the dynamics of these theories, which is encoded in the physical, that is diffeomorphism invariant, observables of the theory. However, the construction of these quantities is extremely complicated, due to the non-linear structure of the theory. This project aims at developing computational and perturbative techniques in order to construct physical observables in quantum gravity theories, to investigate their properties, and to consider implications in particular for cosmology. Perturbative methods for the computation of gauge invariant observables have become available recently. These methods have to be improved and further developed. This will be achieved by considering and comparing non-perturbative and perturbative approaches to quantum gravity. If successful the project will have an impact on our understanding of classical and quantum dynamics in general relativity. This project will enable the applicant to return to Europe, to build up a network of collaborators, and to work at one of the leading European centres for research in quantum gravity.'

Introduzione (Teaser)

Scientists have in recent years gained a solid understanding of the kinematical structures provided by candidate theories of quantum gravity. Researchers are now striving to understand the dynamics of these theories.

Descrizione progetto (Article)

After furthering their knowledge of quantum gravity (QG) theories such as loop QG, spin foam models and causal dynamical triangulations, scientists want to investigate the dynamics of these theories by developing computational and perturbative techniques. This research is aimed, in particular, at analysing the implications of their properties for cosmology.

The 'Physical observables in quantum gravity' (Observables in QG) project team notes that all these theories use some kind of discreteness either as an auxiliary structure or as a derived property. They add that this opens the question of how this discreteness interacts with the symmetry at the heart of general relativity, namely the so-called diffeomorphism symmetry.

During the seven month of this project, researchers undertook the first steps to discuss representations of the diffeomorphism group in discretised theories of QG. After providing a clear definition of diffeomorphisms in discretised theories, they succeeded in showing that in general diffeomorphism symmetry is broken on the discretised level. The scientist then examined possible approaches to obtain consistent dynamics for quantum theories of gravity.