New Developments in String Theory

我们对物理宇宙的理解建立在两个基石上：量子力学和广义相对论。量子力学用统计概念来描述亚原子粒子来预测它们的行为。相比之下，广义相对论，即爱因斯坦的引力理论，利用时空几何在天文尺度上提供了对物理的精确描述。将这两种理论及其截然不同的自然观统一在一个框架内，仍然是21世纪理论物理学家面临的突出的基本问题。弦理论在这一探索中处于领先地位。弦理论的显著特征是，与其说基本粒子是点状的，不如说它们是向一个方向延伸的，即“弦”。这种方法的一个值得注意的特性是，引力是这些理论的必要组成部分。然而，统一量子引力理论的负担是在从亚原子到天文尺度的所有尺度上一致地描述物理。目前，我们的知识还不足以回答弦理论是否真的实现了这一目标，因此还有大量的工作要做，以了解这个非常丰富和复杂的结构及其物理含义。为了实现这一最终目标，我正在进行的研究计划是由三个基本问题构成的：1)组织量子场论空间的一般原理是什么？2)在量子引力理论中，时空的基本结构是什么？什么物理原理支配着非平衡系统的行为？近年来，我的研究表明，这些问题的答案是由弦理论中出现的概念和方法与理论物理中不同领域的想法的惊人融合而统一的。特别地，我的研究吸引了三个主题：来自弦理论的量子引力的“全息”描述；重正化群作为研究量子场论空间的框架在量子信息理论中发展的量化量子系统纠缠的技术。随着最近的进展结合了这些想法，我乐观地认为，在未来五年内，我可以在回答上述三个问题方面取得重大进展。我的研究项目将开发新的概念和方法来解决上述基本问题，并推进我们对量子场论和量子引力的基本理解。此外，虽然最近的进展已经在看似不同的理论物理领域之间产生了令人惊讶的联系，例如粒子物理和量子信息理论，但我的工作结果无疑将加深这些联系并开辟新的研究途径，可能会产生凝聚态理论和量子信息的衍生产品。当然，通过这些调查培养的学生和博士后研究人员将处于研究的前沿。就更广泛的影响而言，80年前，人们不可能预测到对量子力学的理解会导致无线互联网设备的出现。同样，现在也不可能预测当前量子场论和弦理论的研究最终将如何影响我们的生活或我们孩子的生活。然而，历史表明，人类不断寻求更好地了解物质宇宙，总是会带来新技术，造福我们的文明。

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.