New Developments in String Theory

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Our understanding of the physical universe rests on two cornerstones: quantum mechanics and general relativity. Quantum mechanics describes subatomic particles using statistical notions to predict their behavior. In contrast, general relativity, Einstein's theory of gravity, provides a precise description of physics on astronomical scales using spacetime geometry. Unifying these two theories and their remarkably dissimilar views of nature in a single framework remains the outstanding fundamental question for theoretical physicists in the twenty-first century. String theory stands as the leading candidate in this quest. The distinguishing feature of string theory is that rather than regarding elementary particles as point-like, they are extended in one direction, i.e., "strings." A noteworthy property of this approach is that gravity emerges as a necessary ingredient of these theories. Yet the burden of a unified quantum theory of gravity is to consistently describe physics on all scales, from subatomic out to astronomical scales. At present, our knowledge is inadequate to answer whether string theory truly fulfills this goal and so a great deal of work remains to understand this remarkably rich and complex structure and its physical implications.Towards this ultimate goal, my ongoing research program is framed by three fundamental questions:1) What general principles organize the space of quantum field theories?2) What is the underlying structure of spacetime in a quantum theory of gravity?3) What physical principles govern the behaviour of out-of-equilibrium systems?In recent years, my research has shown that the answers to these questions are unified by a surprising confluence of concepts and methods emerging from string theory with ideas from different areas in theoretical physics. In particular, three themes upon which my research draws are: the `holographic' description of quantum gravity coming from string theory; the renormalization group as framework to study the space of quantum field theories; and techniques developed in quantum information theory to quantify entanglement in quantum systems. With recent advances combining these ideas, I am optimistic that I can achieve significant progress towards answering all three of the above questions in the next five years.My research program will develop new concepts and methods to address the fundamental questions posed above and advance our fundamental understanding of quantum field theory and quantum gravity. Further, while recent progress has already produced glimpses of surprising connections between seemingly disparate areas of theoretical physics, e.g., particle physics and quantum information theory, the results of my work will undoubtedly deepen these connections and open new avenues of research, possibly producing spin-offs for condensed matter theory and quantum information. Of course, the students and postdoctoral researchers trained through these investigations will be well-positioned at the cutting-edge of research.In terms of broader impact, eighty years ago, it would have been impossible to predict that understanding of quantum mechanics would lead to wireless internet devices. So too, it is impossible now to predict how the current research in quantum field theory and string theory will ultimately impact on our lives or those of our children. However, history shows that humanity's continuing quest to better understand the physical universe has always lead to new technologies to benefit our civilization.