Emergent Continuum Physics from Quantum Gravity

Quantum Gravity (QG) aims to provide a coherent synthesis of General Relativity (GR) and Quantum Mechanics (QM). A non-perturbative quantization of gravity leads to the disappearance of spacetime related notions, indicating that continuum gravity and physics may in fact just be emergent phenomena, as suggested also by the thermodynamic interpretation of classical gravity. By studying how continuum physics may emerge from QG and what are the typical effects it may produce, one expects to strengthen the connection with currently observable physics and to gain insights about the true nature of what we believe to be fundamental concepts, thus alleviating the main obstacles which prevent a better understanding of QG. In this thesis, we adhere to this emergent perspective and study the crucial problem of extraction of continuum physics from QG. For a large part of the work, we approach the problem from the point of view of the microscopic QG theory (more precisely, within the Tensorial Group Field Theory (TGFT) approach to QG), focusing especially on obtaining cosmological systems. However, we also provide some simple examples of phenomenological methods based on the combination of thermodynamic considerations with QG theoretical evidences that lead to QG corrections to continuum gravitational physics