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Bohmian Quantum Gravity and Cosmology
Published in Xavier Oriols, Jordi Mompart, Applied Bohmian Mechanics, 2019
Nelson Pinto-Neto, Ward Struyve
Quantum gravity aims to describe gravity in quantum mechanical terms. How exactly this needs to be done remains an open question. Various proposals have been put on the table, such as canonical quantum gravity, loop quantum gravity, string theory, etc. These proposals often encounter technical and conceptual problems. In this chapter, we focus on canonical quantum gravity and discuss how many conceptual problems, such as the measurement problem and the problem of time, can be overcome by adopting a Bohmian point of view. In a Bohmian theory (also called pilot-wave theory or de Broglie–Bohm theory, after its originators de Broglie and Bohm); a system is described by certain variables in space-time such as particles or fields or something else, whose dynamics depends on the wave function. In the context of quantum gravity, these variables are a space-time metric and suitable variables for the matter fields (e.g., particles or fields). In addition to solving the conceptual problems, the Bohmian approach yields new applications and predictions in quantum cosmology. These include space-time singularity resolution, new types of semiclassical approximations to quantum gravity, and approximations for quantum perturbations moving in a quantum background.
Physics, science and technology in the future
Published in Kléber Ghimire, Future Courses of Human Societies, 2018
The effort to unify gravity with the other three fundamental forces is called quantum gravity. It postulates the existence of a virtual particle called the graviton, which would be the mediating element in gravity interactions. The recent discovery of the gravitational waves predicted by Einstein’s general theory of relativity opened up a new front to further understanding the universe. The discovery also represents the first experimental evidence for quantum gravity, a hypothetical union of quantum mechanics and general relativity. It is possible that an understanding of quantum gravity will not merely consolidate the theories, but will rather introduce a fundamentally new understanding of space and time. Will there be some breakthrough in these areas allowing the emergence of whole new fields that were completely untapped previously, as some scientists have suggested (Wilczek, 2016, pp. 33–39)?
Geometric theory of topological defects: methodological developments and new trends
Published in Liquid Crystals Reviews, 2021
Sébastien Fumeron, Bertrand Berche, Fernando Moraes
A major contemporary challenge in physics is to find an extension of General Relativity able to describe gravity at all energy scales, in particular at the very beginning of the universe. This is the mission devoted to quantum gravity theories, which have the daunting task of reconciling Einstein's general relativity and quantum field theory. Despite promising attempts, including superstring theories, M-theory or quantum loop gravity, no proposal is entirely satisfactory up to now, and even so, the energy scales required to test these theories are far beyond our current scientific capabilities. A way out of this gridlock is to rely on simpler models that capture the essential features of quantum gravity but remain connected to low-energy-physics systems, i.e. analog gravity. The rare pearl was first introduced in a seminal paper by Deser, Jackiw and 't Hooft [141]: 2 + 1 gravity with point-particle sources.
Black hole entropy, the black hole information paradox, and time travel paradoxes from a new perspective
Published in Journal of Modern Optics, 2020
Our current view of nature is that it is composed entirely of quantum fields (although the proper description of quantum gravity is still undecided). All physics can be regarded as ultimately derived from an enormous path integral with the form where the action is now a functional of all fields over all spacetime. The gravitational field is described by a metric tensor . The other fields will be represented by . contains all physically distinct field configurations that are consistent with whatever boundary conditions are imposed.