Loop Quantum Gravity with Cosmological Constant

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Einstein's General Relativity (GR) is the theory describing the physics of the classical gravitational field. The theory of GR has made tremendous progress in understanding the fundamental aspects of space and time and has been successful in making predictions for the evolution of the universe and various astrophysical phenomena. However it is well-known that the theory of GR is incomplete. It loses its capability of making predictions in extremely strong gravitational fields, e.g. inside a black hole or at the very early stage of the universe near the big bang. One of the most fundamental open questions in physics is how to complete GR in order to predict physics in an extremely strong gravitational field. The complete theory of gravity that we are searching for is called "Quantum Gravity". The theory of Quantum Gravity should play a crucial role in describing the physics inside black holes and helping us to understand the early universe near the big bang. Eventually Quantum Gravity will lead us to a revolutionary understanding of space and time. This award supports the development of a candidate Quantum Gravity theory known as "Loop Quantum Gravity" (LQG), which offers significant promise in addressing the questions posed. The work supported by this award focuses on developing the theory of LQG with a cosmological constant in 4 dimensions, in particular the spinfoam formulation of theory. The main objectives of this project are: (1) Investigating the continuum limit of the theory, in particular the emergence of smooth spacetime geometries and Einstein equations from the spinfoam amplitude, and relating the spinfoam formulation to the recent program of emergent gravity from quantum information, (2) analyzing the quantum effects of curvature singularities in the framework of spinfoams, and to extract physical observables, and (3) developing a canonical framework closely related to the spinfoam formulation with a cosmological constant.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.