Zenith Grant Awardee

Steven Giddings

University of California, Santa Barbara

Project Title

Information-theoretic foundations for quantum spacetime and gravity

Project Summary

All known physical phenomena are presently described via the framework of \'quantum field theory\'. This framework is based on essential principles: quantum mechanics, special or general relativity, and locality. The latter, locality, states that information cannot propagate faster than the speed of light. This simple statement, combined with the existence of black holes, and the demonstration that they evaporate, has lead to a profound conflict. Specifically, Hawking predicted that since information cannot escape black holes, their evaporation destroys information – violating a basic tenet of quantum mechanics. There are strong indications that such violation of quantum mechanics is not sensible; basic principles of relativity likewise seem robust. However, locality is difficult to precisely formulate, when one accounts for the fact that, at the least, spacetime undergoes quantum fluctuations. The problem may go further than that, and indicate that space and time are not fundamental concepts but instead arise from a more fundamental mathematical structure. If quantum mechanics is taken as essential, this structure should involve a basic description of quantum information, the most basic \'stuff\' of quantum mechanics, and how it transfers and interacts. These ideas can be tested in their ability to describe important gravitational systems: black holes and cosmology.

Technical Abstract

There are growing indications for a deep connection between quantum gravity and quantum information, which may realize ideas of emergent spacetime, from a more basic information-theoretic structure. One indication is the profound conflict between essential principles underlying quantum field theory, seen via black hole formation and evaporation. These are relativistic invariance, quantum mechanics, and locality. It appears difficult to modify the first two, but locality is not obviously robust in a theory of quantum gravity. Validity of quantum mechanics indicates a fundamental role for quantum information; modification of locality suggests that spacetime is not fundamental. Other hints of this come from candidate descriptions of quantum gravity, like the AdS/CFT correspondence. Black holes are an incisive testing ground for these ideas, where one can study the form of quantum information transfer from the interior of a black hole that is necessary to preserve quantum mechanics. Here new aspects of the information problem have emerged, and new paradoxes involving violent effects at horizons have been claimed. I propose to study the possible role of a quantum information-theoretic foundation for spacetime and gravity, and specifically to explore these questions in the test cases of black holes and quantum inflationary cosmology.