String Theory, Black Holes, and the Subatomic Structure of Spacetime

爱因斯坦的广义相对论描述了非常重的物体的物理学。它是一个多世纪前发明的，已经成功地解释了各种各样的实验数据。它的主要特征之一是时空结构的平滑性。量子理论描述的是非常微小事物的物理学。它是在一个世纪前发明的，它也成功地解释了各种各样的实验数据。它的一个关键特征是量子态空间的离散性。在深层次上，这两种理论的关键特征是相互冲突的。对于我们能想象到的大多数系统，比如星系或希格斯玻色子，这不是一个问题，因为我们感兴趣的物体要么非常重，要么非常小。但如果我们想了解黑洞的核心或宇宙的诞生，我们需要一个更好的理论来处理平滑时空和量子跃迁。即使我们可能永远无法接触到黑洞或大爆炸，我们仍然可以通过理论工具和思想实验来解剖和学习有关它们的有价值的东西。我的主要兴趣是了解落入黑洞的量子信息的最终命运，以及更多地了解时空的亚原子结构。为了研究这个问题，我使用了弦理论，这是目前最发达的量子引力框架。近年来，两项相互关联的进展使我的目标更容易实现。第一个进展是弦理论中被称为膜（mem）的高维引力物体的发现，它与一维基本弦共存。膜是万能的，可以用来构建有趣的黑洞。它们还使得从黑洞熵的第一原理第一次得到解释成为可能，熵是一个类似于无序的量，它记录了黑洞在引力坍缩中形成的大量方式。自那时以来，已经取得了很大的进展，但仍有更多的领域有待了解。关注更细粒度的引力信息很重要。为黑洞的微观弦理论建模做出贡献是我研究项目的两个主题之一。第二个进步，被称为全息术，是一个令人惊讶和强大的发现，某些类型的量子引力系统可以被描述为生活在少一个空间维度的非常不同的非引力系统。这让人想起全息图，你只从2D全息图中获得整个3D图像。全息术最初是用弦理论发现的，但后来意识到它是一个更普遍的概念。它将弦理论、粒子理论、引力理论、凝聚态物质理论、早期宇宙宇宙学理论和量子信息理论的各个方面联系在一起，就像一个理论物理学的迷你联合国。为全息术的发展做出贡献是我研究计划的另一个主题。

Einstein's theory of general relativity describes the physics of very heavy things. Invented a bit over a century ago, it has successfully explained a wide variety of experimental data. One of its key features is the smoothness of the fabric of spacetime. Quantum theory describes the physics of very small things. Invented a bit under a century ago, it has also successfully explained a wide variety of experimental data. One of its key features is the discreteness of the space of quantum states. At a deep level, the key features of these two theories are in conflict. For most systems we can imagine, like galaxies or Higgs bosons, this is not a worry, because our objects of interest are either very heavy or very small. But if we want to understand the heart of a black hole or the birth of the cosmos, we need a better theory that can handle both smooth spacetime and quantum jumps. Even if we may never be able to physically touch black holes or big bangs, we can still dissect and learn valuable things about them by recruiting theoretical tools and thought experiments. My main interest is in understanding the ultimate fate of quantum information falling into black holes and knowing more about the subatomic structure of spacetime. To investigate this, I use string theory, which is currently the best developed quantum gravity framework available. Two interrelated advances in recent years have made my goals more accessible. The first advance was the discovery of higher-dimensional gravitating objects in string theory known as (mem)branes, which co-exist alongside the one-dimensional fundamental strings. Branes are versatile, and can be used to build interesting black holes. They also enabled the first explanation from first principles of the entropy of a black hole, a quantity akin to disorganization which codifies the tremendously large number of ways a black hole could be formed in gravitational collapse. Much progress has been made since then, but more territory remains to be understood. Focusing on more fine-grained gravitational information is important. Contributing to microscopic string theory modelling of black holes is one of the twin themes of my research program. The second advance, known as holography, was a surprising and powerful discovery that certain types of quantum gravity systems can be alternatively described in terms of very different-looking non-gravitational systems living in one less dimension of space. This is reminiscent of a hologram where you get the whole 3D image from only the 2D hologram. Holography was originally found using string theory, but was later realized to be a more general idea. It interconnects aspects of string theory, particle theory, gravity theory, condensed matter theory, early universe cosmology theory, and quantum information theory, like a mini United Nations of theoretical physics. Contributing to developing holography is the other main theme of my research program.