Classical and Quantum Aspects of Black Holes, Horizons and Asymptotic Symmetries

施特罗明格和合作者将研究爱因斯坦引力场方程所隐含的自然界的无限对称性，这些对称性是在上一次拨款周期中发现的。它们出现在时空的边界上，既存在于光的无限距离，也存在于快速旋转的黑洞的视界附近。该理论研究在引力波、引力记忆、即将到来的事件视界望远镜天文观测中具有潜在的应用价值。事件视界望远镜是一项利用遍布全球的无线电天线阵列对黑洞进行空前分辨率观测的计划。该奖项支持的工作也将解决霍金？S黑洞信息悖论，该悖论假定信息在黑洞中可能不守恒。在过去的几年里，这个小组发现了三种现象的精确三角等价，这三种现象在各种各样的物理系统中无处不在地重复出现，并且已经单独研究了半个多世纪：记忆、软定理和渐近对称性。量子场论中的软定理将任何多粒子散射过程与“软”（即低能）粒子（如引力子）插入到相同的过程中，而没有软粒子。渐近对称（如BMS）是在无穷远处对物理数据起非平凡作用的微分同态。软定理可以导出为与渐近对称相关的守恒律的量子矩阵元素。因此它们具有相同的物理内容。三角的第三个角是封闭的，注意到引力记忆效应的Braginsky-Thorne公式正是Weinberg软引力子定理的傅里叶时间变换。在QED、Yang-Mills理论、重力、任何维度中，有或没有超对称，一个角落里有主导、次主导或次主导软定理，以及涉及异常的量子三角形，这些都是三角形反复出现的例子。这种对先前已被充分理解的现象的等价性的发现使我们能够发现全新的现象。已知三角形的一个角，我们现在知道如何找到另外两个角。这个项目研究的是引力三角形。将三角形结构应用于黑洞，表明黑洞远不是没有特征的物体，即使是经典的黑洞也有无限的“软毛”。霍金在1975年提出的“信息丢失”理论中就假定不存在这些显著特征，因此该理论无效。这一发现为黑洞信息悖论的研究提供了新的思路。在另一个方向上，天文观测表明存在近乎极端的克尔黑洞，其视界以接近光速的速度旋转。广义相对论暗示，极端克尔的高红移近视界区域的动力学，包括最内层稳定圆轨道（ISCO），是由一个无限维的涌现共形对称控制的。一般来说，物理系统的对称性既可以有效地表征观测数据，也可以对观测数据产生显著的影响。精确的黑洞光谱学已经发展到这样一个阶段，天文学家开始用各种巧妙的方法观察受这种共形对称性支配的时空区域。拟议中的项目将对共形对称的潜在观测结果进行系统的探索，特别是对已经处于数据收集早期阶段的事件视界望远镜。

Strominger and collaborators will investigate the infinitely many symmetries of nature implied by the Einstein equations for the gravitational field and discovered under the last grant cycle. These arise at the boundaries of spacetime, both at infinite light like distances and near the horizon of a rapidly spinning black hole. The theoretical research has potential applications to gravitational waves, gravitational memory, upcoming astronomical observations at the Event Horizon telescope. The Event Horizon telescope is an initiative to create observations of black holes of unparalleled resolution using an array of radio antennas located across the globe. The work supported by this award will also tackle Hawking?s black hole information paradox, which posits that information may not be conserved in a black hole. In the last few years, this group has discovered an exact triangular equivalence of three phenomena which recur ubiquitously across a wide variety of physical systems and have been separately studied for over a half century: memory, soft theorems, and asymptotic symmetries. Soft theorems in quantum field theory relate any multi-particle scattering process with the insertion of a 'soft' (i.e. low-energy) particle such as a graviton to the same process without the soft particle.Asymptotic symmetries (such as BMS) are diffeomorphisms which act nontrivially on the physical data at infinity. The soft theorems can be derived as the quantum matrix elements of the conservation laws associated to the asymptotic symmetries. Hence they have the same physical content. The third corner of the triangle is closed by noting that The Braginsky-Thorne formula for the gravitational memory effect is precisely the Fourier transform in time of the Weinberg soft graviton theorem. There are many recurring instances of the triangle: in QED, Yang-Mills theory, gravity, in any number of dimensions, with or without supersymmetry, with leading, subleading or subsubleading soft theorems in one corner, and quantum triangles involving anomalies. This discovery of the equivalence of previously well-understood phenomena enables us to discover brand new phenomena. Given one corner of the triangle, we now know how to find the other two. This project investigates gravitational triangles. Applied to black holes, the triangular structure was shown to imply that, far from being bald featureless objects, even classical black holes carry an infinite head of 'soft hair'. The absence of any such distinguishing features was presumed in Hawking's 1975 argument for information loss, which is therefore invalidated. This insight suggests new lines of investigation into the black hole information paradox which the group will pursue. In another direction, astronomical observation suggests the existence of near-extreme Kerr black holes whose horizons spin at nearly the speed of light. General relativity implies that the dynamics of the high-redshift, near-horizon region of extreme Kerr, which includes the innermost stable circular orbit (ISCO), is governed by an infinite-dimensional emergent conformal symmetry. Symmetries of physical systems in general may both usefully characterize and have striking consequences for observational data. Precision black hole spectroscopy has advanced to the stage where astronomers are beginning to observe -- with a variety of ingenious methods -- the regions of spacetime governed by this conformal symmetry. The proposed project will undertake a systematic exploration of potential observational consequences of the conformal symmetry, in particular for the Event Horizon telescope which is already in the early stages of data collection.