Constraining gravity with cosmology

最近的过去见证了宇宙学的惊人成功，以极高的精确度限制了宇宙的结构、内容和演化。因此，当前宇宙学的一个重点是了解这种演化背后的动因，确定宇宙在早期和晚期加速膨胀背后的基本物理，以及暗能量和暗物质的性质。这项事业的关键是彻底了解引力本身--这是自然界中最不为人所知的力。具体地说，这涉及到测试、约束(并可能检测出与我们目前最有效的理论：广义相对论的偏差)。随着新的观测窗口的出现(例如，第一次探测到引力波)以及其他成熟的引力探测器(例如，对宇宙微波背景的观测)，我们目前拥有大量显著且持续增长的数据，使我们能够精确地测量引力现象。与此同时，在理解一致的引力理论必须具备哪些特征方面的最新理论进展，使我们能够对重力如何行为以及它如何与宇宙中的物质相互作用施加额外的强有力的限制。总而言之，这意味着我们目前拥有前所未有的强大仪器，可以精确地识别和约束引力的性质。考虑到它们起源于不同的物理领域，到目前为止，这些仪器还没有被联合使用，但它们本质上的不同操作方式意味着它们实际上是理想的互补，以各种不同的方式测试和探测重力。因此，这项研究计划旨在充分利用这种互补性，整合各种方法，从开发数据驱动的数值代码到实施高能粒子物理的理论界限，以获得迄今最系统和最严格的引力界限。通过这种方式，我们将能够彻底探索引力的本质，在这个过程中测试它的几个基本属性。

The recent past has witnessed phenomenal successes in cosmology, constraining the structure, content and evolution of the Universe with tremendous accuracy. Consequently, a current focus of cosmology is to gain an understanding of the agents behind this evolution, identifying the fundamental physics behind the accelerated expansion of the Universe at early and late times and the nature of dark energy and dark matter. Key to this enterprise is thoroughly understanding gravity itself - the least well-understood of the known forces in nature. Specifically, this involves testing, constraining (and potentially detecting deviations from) our current best working theory: General Relativity. With the emergence of new observational windows (e.g. the first detections of gravitational waves) in addition to other well-established probes of gravity (e.g. observations of the cosmic microwave background), we presently have a remarkable and continuously growing amount of data allowing us to precisely measure gravitational phenomena. Simultaneously, recent theoretical advances in understanding what features a consistent theory of gravity must possess, enable us to impose additional strong restrictions on how gravity can behave and and how it interacts with matter in the universe. Altogether this means we currently have at our disposal an unprecedented amount of powerful instruments to precisely identify and constrain the nature of gravity. Given the different areas of physics they originate from, these instruments have not been used jointly so far, yet the qualitatively different ways in which they operate means they in fact ideally complement one another, testing and probing gravity in a variety of different ways. This research program therefore aims to take full advantage of this complementarity, integrating methods ranging from the development of data-driven numerical codes to the implementation of theoretical bounds from high-energy particle physics in order to obtain the most systematic and tight bounds on gravity yet. In this way, we will be able to thoroughly probe the nature of gravity, testing several of its fundamental properties in the process.