Explorations in Quantum Gravity: Cosmological and Black Hole Spacetimes

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Einstein’s theory of general relativity, though immensely successful in describing the evolution of the universe and the dynamics of black holes, breaks down at singularities such as the big bang and inside the black holes. It has been widely believed that a quantum theory of gravity overcoming the problems of singularities would give answers to long-standing questions in Einstein’s theory, such as if there is space and time beyond the big bang, what replaces big bang and black hole singularities, what is the physics beyond Einstein’s theory and how does it leave observational signatures. This NSF funded research aims to address various such fundamental questions using techniques of loop quantum gravity. A primary objective of this research would be to discover new physics at the Planck scale which is responsible for the resolution of singularities and robust observational signatures in the cosmic microwave background by using a combination of rigorous analytical, phenomenological and state-of-the-art numerical methods for various quantum gravitational cosmological and black hole spacetimes. Progress in this area of research will benefit communities and scientists engaged in classical and quantum gravity and cosmology and may lead to answers to fundamental questions which are of interest to the public. Graduate students and postdoctoral researchers will be trained on state-of-the-art research on quantum gravity. The primary goal of this research is to discover the new physics emerging from the quantum properties of spacetime and generalize the results on quantum bounce, which replaces the big bang singularity, to anisotropic and inhomogeneous spacetimes. Using techniques of loop quantum gravity it aims to address fundamental issues such as the fate of singularities in quantum gravity, the way quantum gravity affects the physics of the very early universe and black holes, and reliable potential observational signatures of quantum gravity in the cosmic microwave background. These fundamental questions will be explored by: (i) systematically investigating the quantization and resulting physics of different spacetimes including anisotropies, inhomogeneities and black holes, (ii) exploring phenomenological implications of quantum gravity by analyzing effects on cosmological perturbations and (iii) addressing foundational issues in quantum cosmology such as the quantum to classical transition and quantum probabilities. This research is expected to significantly broaden and advance our understanding of the physics of quantum gravity and lead to insights on the nature of spacetime beyond Einstein’s theory of general relativity.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.