Gravity remains the final force of nature to reveal its quantum composition. To witness quantum gravity one must probe the most energetic scenes in the universe, such as the first fraction of a second after the big bang or the fiery center of a black hole. My research examines quantum physics, including quantum gravity, in these exotic environments. My basic tools are general relativity, quantum field theory (QFT), and the Anti-de Sitter/Conformal Field Theory (AdS/CFT) correspondence.
Quantum field theory in curved spacetime
The marriage between general relativity and quantum physics is not an easy one. While the basic construction of QFT on curved spacetime is decades old, fundamental questions remain. Physicists successfully use QFT on curved spacetime to describe the equation of state of compact objects as well as fluctuations in the early universe. But the same theoretical tools fail in other settings, most notably in the vicinity of black holes, leading to the black hole information paradox. My interests in this field include developing new techniques for quantum perturbation theory, constructing integrable QFTs on curved backgrounds, and understanding the structure of perturbative quantum gravity.
Quantum aspects of cosmological inflation
Modern precision measurements in cosmology probe the universe at an era when the energy density was several orders of magnitude greater than can be achieved in terrestrial particle colliders. One example is the PLANCK satelite's mapping of temperature variations in the cosmic microwave background. These measurements have transformed early universe cosmology into the “final frontier” of high-energy physics. The increasing accuracy of observation demands a mirrored increase in the accuracy of our understanding of quantum effects in the early universe. My contributions to this field work to achieve this new level of precision. For example, one product of my investigations has been the formulation of a set of “quantum cosmic no-hair theorems.” These theorems make precise the intuitive, yet debated, statement that during an epoch of cosmological inflation, information about the initial quantum state becomes “washed out” and inaccessible to late-time observers with finite resources. Through results such as these, my work has helped place the treatment of quantum effects in cosmology on a rigorous mathematical footing.
Bulk reconstruction in AdS/CFT
AdS/CFT is a duality – an equivalence relation – between two seemingly disparate theories: a “bulk” string theory which includes quantum gravity, and a “boundary” conformal field theory (CFT) which does not include gravity. Through this duality, AdS/CFT provides a putative UV-complete theory of quantum gravity in terms of the non-gravitational CFT. One of my long-term interests in this field is understanding the process of “bulk reconstruction,” i.e., the process of constructing the bulk spacetime dual to a given quantum state in the CFT. Only once this reconstruction is understood will we be able to use AdS/CFT to resolve the singularities of classical general relativity, such as the big bang and the singularities hidden within black holes, or resolve the black hole information paradox.