About this Research Topic
Our current best understanding of the dynamics of spacetime is based on General Relativity. It is a very successful description in excellent agreement with observations at large scales, but breaks down as we zoom in on the small-scale structure of spacetime where quantum effects matter. This necessitates the development of a quantum theory of gravity that describes spacetime at and beyond the Planck scale. Coarse-graining techniques in quantum gravity literally allow us to ’zoom in‘ and probe quantum spacetime. Over the last few years, these techniques have been gaining traction in the quantum gravity community and have triggered progress in various approaches, most notably asymptotically safe gravity, but also spin foams/ Loop Quantum Gravity, group field theories, tensor models and dynamical triangulations, and even in holographic settings. This Research Topic aims to provide an overview of the state-of-the art of these techniques and the underlying conceptual ideas, with a clear and open discussion of unanswered questions and important challenges. Moreover, a critical discussion on the use of Renormalization Group techniques to connect models of quantum spacetime to phenomenology, in black holes, cosmology and also particle physics, will constitute an important part of this article collection.
A particular motivation for this broad collection of articles lies in the diversity of the research field: Due to the severe difficulty of reaching the Planck scale experimentally, many different approaches to quantum gravity are being developed simultaneously. Various important insights have been reached on the quantum structure of spacetime in diverse models, and a key challenge is to understand whether and how a point of convergence between different approaches can be reached. In order to study this, a common language between various approaches should be developed, and coarse graining techniques have become a novel link between different approaches over the last few years. This collection aims at strengthening this link by soliciting introductory reviews to each topic. All authors of the collection will be invited to submit questions to the authors of the reviews. The editorial team will make a selection of these to forward to the author. Thereby, each review will contain a question-section at the end that will provide answers to questions posed from experts of other quantum-gravity approaches. This will contribute to stimulating a sustained dialogue, and ensure a fair and open representation of the state-of-the-art, including an assessment of the open questions and problems.
Specifically, the collection will contain introductory reviews on coarse graining/Renormalization Group flows in asymptotically safe gravity, holographic settings, group field theories, Loop Quantum Gravity, spin foams and tensor models. Invited articles should focus on the conceptual and technical questions of the application of coarse-graining techniques in quantum gravity. In particular, we welcome articles aiming at bridging the gap between various approaches to quantum gravity, based on the common use of coarse-graining techniques.
Keywords: quantum gravity, renormalization group, coarse graining
Important Note: All contributions to this Research Topic must be within the scope of the section and journal to which they are submitted, as defined in their mission statements. Frontiers reserves the right to guide an out-of-scope manuscript to a more suitable section or journal at any stage of peer review.