Research in Classical and Quantum Gravity

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This award supports research in gravitational physics at the University of California, Santa Barbara. Many of the deepest problems in theoretical physics revolve around combining Einstein's theory of general relativity with quantum theory. The resulting theory is called "quantum gravity" and is needed to better understand the origin of the universe, the nature of space and time on small scales, and what happens inside black holes. The research supported by this award will use the latest techniques and tools to try to answer some of these fundamental problems. An essential part of the project is the training of graduate students and postdoctoral researchers in the knowledge and techniques that are central to understanding and discovery in gravitational physics. Through a range of forums from public lectures, to informing media reporters, the Principal Investigators will disseminate the directions and results of their research to a broad audience. Society at large will benefit by increasing their understanding of science and the world they live in.James Hartle will continue exploring the interface between quantum mechanics and cosmology. He will work on extending the predictions of the no-boundary quantum state of the universe for observations today to increasingly general and detailed situations. He will further develop the generalizations of quantum mechanics that are necessary for cosmology and investigate cosmologically motivated extensions of quantum mechanics. He proposes to continue to refine our understanding of the origin of the quasiclassical realm of every day experience as an emergent feature of our quantum universe. Gary Horowitz will investigate a variety of topics in classical and quantum gravity, focussing on singularities and the origin of spacetime. He will explore whether classical singularities can be visible, or must always be hidden behind event horizons. He will also examine a recently discovered connection between potential visible singularities and charged matter. In addition, Horowitz will study how spacetime geometry emerges from a holographic theory of quantum gravity. He will consider the roll of quantum entanglement, but also pursue a new direction based on special cross-sections of the boundary at infinity. Don Marolf will explore a variety of issues in classical and quantum gravity generally related to black holes, thermodynamics, and entropy. While there is already much evidence that black holes are in some sense thermal systems (with entropy proportional to their surface area), and while this is expected to hold deep and fundamental lessons for physics, the argument has not yet been made in complete generality. Marolf will explore the required extensions and the resulting implications. Another part of his work seeks to more deeply understand so-called holographic descriptions of gravity, where phenomena in a dynamical spacetime are in fact equivalent to the quantum physics of a seemingly very different non-gravitating system. In this regard, Marolf is particularly interested in understanding the dictionary that allows one to translate physics inside black holes into the language of the non-gravitating formulation.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.