Explorations in Quantum Gravity: Cosmological and Black Hole Spacetimes

Though Einstein’s theory of General relativity is immensely successful in describing the evolution of our Universe from the moments after the Big Bang till the present epoch, it breaks down near the cosmological and black hole singularities. The fundamental questions about the resolution of singularities, initial conditions of the universe, and the emergence of space and time from the Big Bang have remained open for many decades. Answering these questions requires a union of gravity and quantum theory, which is one of the fundamental problems in theoretical physics. In recent years, progress in applying techniques of loop quantum gravity has allowed us to concretely answer these questions in various cosmological and black hole spacetimes. This award aims to explore quantum gravity effects in various spacetimes to understand how to resolve problems of singularities, how to extract new physics beyond Einstein’s General Relativity, and how to potentially test this new physics using cosmic microwave background experiments. Progress in answering these long-standing fundamental questions will not only benefit the wider community but also scientists engaged in research in classical and quantum aspects of gravity, cosmology, and high-energy physics. Graduate students will be trained in solving complex problems using rigorous analytical and computational techniques. The main goal of this research is to explore new physics emerging from the quantization of gravity using non-perturbative techniques employed in loop quantum gravity. In the last decade, loop quantization of various cosmological and black hole spacetimes has provided important insights into the resolution of singularities and potential signatures in the cosmic microwave background. This award aims to answer multiple fundamental questions in this approach. The goals include: (i) Understanding the way quantum gravity effects affect the Mixmaster dynamics and singularities in anisotropic models and the fate of singularities in inhomogeneous spacetimes, such as Gowdy models; (ii) The way different regularization and quantization ambiguities affect the physics at the Planck scale, and how one can phenomenologically constrain these ambiguities; (iii) Exploring the consequences of polymer matter in loop quantized spacetimes; (iv) Loop quantization of black hole spacetimes; and (v) Addressing foundational issues in quantum cosmology such as quantum to classical transition and quantum probabilities. This research is expected to significantly broaden and advance our understanding of the physical implications of quantum gravity and lead to insights into 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.