Research in Classical and Quantum Gravity

该奖项支持加州大学圣巴巴拉分校的引力物理学研究。理论物理学中许多最深奥的问题都围绕着爱因斯坦的广义相对论和量子理论的结合。由此产生的理论被称为“量子引力”，需要更好地理解宇宙的起源，小尺度上的空间和时间的本质，以及黑洞内部发生的事情。这项资助支持的研究将使用最新的技术和工具来尝试回答这些基本问题中的一些。这项工作的一个重要部分是培养研究生和博士后研究人员的知识和技术，这些知识和技术是理解和发现引力物理学的核心。主要研究人员将透过各种论坛，从公开讲座到通知媒体记者，向广大听众传播他们的研究方向和结果。整个社会将受益于增加他们对科学和他们所生活的世界的理解。本研究涉及三个相互关联的研究项目。第一项工作是了解在量子水平上描述引力需要什么样的时空，考虑到量子涨落可能远远超出我们熟悉的经典解的范围。特别是，这种时空的光锥结构可能远非经典，甚至可能是奇异的。我们将研究这种效应对远距离观测者的影响，重点关注所谓的统一性和边界因果性。虽然现在人们认为，包括导致时空改变拓扑结构的波动是一致的，但研究人员将研究这种水平的波动是否实际上是基本原理所要求的。该项目的第二部分进一步研究波动拓扑的物理后果以及大宇宙可能与物理上独立的封闭宇宙（通常称为婴儿宇宙）相互作用的相关过程。最近的研究表明，这至少部分地解决了近50年来的黑洞信息问题，但观察者在一个古老的蒸发黑洞中所经历的实际物理现象仍有待完全理解。该项目还将研究对上述封闭宇宙的相关影响，从而对宇宙学和整个宇宙的影响。最后部分探讨了已有50年历史的宇宙审查假说和经典引力中的奇点结构。已知的在AdS边界条件下对宇宙审查的某些版本的违反将更详细地分析，着眼于1)与所谓的高能物理弱引力猜想的联系，以及2)在渐近平坦时空中开发可能的进一步反例。某些黑洞奇点对参数表现出很强的敏感性这一事实也将被探讨。在这三个研究项目中使用的方法将主要是分析方法，尽管这些方法将辅以台式计算机上的数值计算。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This awards supports research in gravitational physics at the University of California, Santa Barbara. Many of the deepest problems in theoretical physics revolve around combining Einstein's theory of general relativity with quantum theory. The resulting theory is called "quantum gravity" and is needed to better understand the origin of the universe, the nature of space and time on small scales, and what happens inside black holes. The research supported by this grant will use the latest techniques and tools to try to answer some of these fundamental problems. An essential part of the work is the training of graduate students and postdoctoral researchers in the knowledge and techniques that are central to understanding and discovery in gravitational physics. Through a range of forums from public lectures, to informing media reporters, the Principal Investigators will disseminate the directions and results of their research to a broad audience. Society at large will benefit by increasing their understanding of science and the world they live in.The research involves three inter-related programs of research. The first works to understand what sort of spacetimes are needed to describe gravity at the quantum level, taking into account the quantum fluctuations that may range far beyond familiar classical solutions. In particular, the light-cone structure of such spacetimes may be far from classical, and may even be singular. We will investigate the implications of such effects for distant observers, focusing on properties called unitarity and boundary causality. And while it is now understood to be consistent to include fluctuations that cause the spacetime to change topology, the investigators will study whether fluctuations at this level are in fact required by fundamental principles. A second part of the project further investigates the physical consequences of fluctuating topology and the associated processes by which a large universe may interact with a physically-separate closed universe (often called a baby universe). It was shown recently that this at least partially resolves the nearly 50-year-old black hole information problem, but the actual physics experienced by an observer inside an old evaporating black hole remains to be fully understood. The project will also study associated implications for the above-mentioned closed universes, and thus for cosmology and for our universe as a whole. The final part probes the 50-year-old cosmic censorship hypothesis and the structure of singularities in classical gravity. Known violations of certain versions of cosmic censorship with AdS boundary conditions will be analyzed in more detail with an eye toward 1) connections to the so-called weak gravity conjecture of high energy physics and 2) developing possible further counter-examples in asymptotically flat spacetimes. The fact that certain black hole singularities show strong sensitivity to parameters will also be explored. The methods employed in all three programs of research will be primarily analytic, though these will be supplemented with numerical calculations on desktop computers.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.