Gravity and Entanglement

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Some of the grandest open questions in theoretical physics lie directly at the interface of quantum mechanics and gravity. How did our universe begin? How will it end? What is dark energy? What is inside a black hole? Each of these questions is fundamental to our understanding of nature, but none of them can be answered in a framework that does not include both gravity and quantum physics. Recent developments in string theory have brought us closer than ever before to answering questions like these. Twenty years ago, researchers in string theory discovered a stunning connection between the physics of quantum gravity and the physics of quantum field theories, the well-understood mathematical models that physicists use to understand elementary particles and their interactions. Through this connection, known as the AdS/CFT correspondence, quantum gravity questions that were previously impossible to answer can be translated into much simpler questions that can be answered by quantum field theory. A very basic question about AdS/CFT is to understand how the physics of dynamical spacetime (the key feature of Einstein's theory of gravity) can be seen to emerge from the physics of ordinary quantum field theories. Recently, there has been a great deal of exciting progress suggesting that the answer to this question lies in the emerging field of quantum information theory (the theory behind quantum computers). According to work by our group and others, the phenomenon of quantum entanglement plays a central role in understanding nature of spacetime and gravity; this observation is leading the way to a better understanding of how gravity works at a fundamental level. For example, it is now understood that certain measures of entanglement in quantum field theory correspond directly to measures of geometry in the corresponding gravitational theory. Using this, we have shown that in some situations, the Einstein equations which govern the dynamics of spacetime and its interactions with matter can be deduced directly from the physics of quantum entanglement in the corresponding field theory. In the proposed research, I plan to exploit these emerging connections between gravity and quantum information theory in various ways. I would like to extend our derivation of Einstein's equations to a wider class of field theory states and investigate possible quantum corrections to these equations. I plan to extend some earlier work to investigate the gravitational implications of various constraints of entanglement coming from quantum information theory. Finally, I plan to explore a scenario that we have recently proposed by which the AdS/CFT correspondence might be used to provide a model of cosmology and help us to better understand our universe's beginning, its accelerating expansion through dark energy, and its end.