DFG-NSF: Observational Tests of Covariant Emergent Gravity

这里提出的项目旨在测试对暗物质和暗能量的新解释。我们想研究这个理论是否与银河系自转曲线和强引力透镜的观测结果相符。有压倒性的证据表明，宇宙包含两个鲜为人知的引力源：暗物质和暗能量。它们可以被共同参数化为具有压力和能量密度的流体。这使得将它们纳入广义相对论变得容易。但它们的微观特性以及它们的起源仍然未知。将暗物质描述为流体效果很好，但特别是对于星系的动力学，它有各种缺点。例如，它预测了星系核心的密度峰值和围绕较大宿主的太多小卫星星系，这两种情况都没有被证实。这种不同的解释是，引力定律必须改变，这就是所谓的“修正引力”。修正后的引力对星系很有效，但在其他情况下就不那么有效了，特别是在早期宇宙和星系团中。在这个项目中，我们想探索真相可能在中间的某个地方。为此，我们使用最近开发的一个框架，称为“协变涌现引力”。“协变突现引力改变了星系尺度上的正常引力，它也产生了暗能量。以前的工作表明，这一理论很好地符合一些现有的数据。该项目的一个工作项目是更详细地研究它是否与银河系旋转曲线和引力透镜（已有数据）相吻合。协变涌现引力进一步描述了低温下的凝聚态。然而，在高温下，修正重力的影响应该逐渐消失。为了理解这是如何发生的，以及在什么情况下发生的，必须进一步发展这一理论。如果成功的话，这个项目将为暗物质的性质提供强有力的经验证据，并解决自20世纪30年代以来一直困扰天体物理学家的一个谜团。

The here proposed project aims to test a new explanation for dark matter and dark energy. We want to investigate whether the theory fits with the observations of galactic rotation curves and strong gravitational lensing.Evidence is overwhelming that the universe contains two little-understood sources of gravity: dark matter and dark energy. They can be collectively parameterized as fluids with pressure and energy-density. This makes it easy to incorporate them into general relativity. But their microscopic properties as well as their origin are still unknown. Describing dark matter as a fluid works well, but especially for the dynamics of galaxies, it has various shortcomings. It predicts, for example, density peaks in galactic cores and too many small satellite galaxies around larger hosts, neither of which has been observed.For galaxies, a different explanation for our observation works better. This different explanation is that the law of gravity must be changed, which is known as "modified gravity". Modified gravity works well for galaxies, but not so well in other situations, notably in the early universe and for galaxy clusters.In this project we want to explore the idea that the truth may be somewhere in the middle. For this, we use a recently developed framework called "Covariant Emergent Gravity." Covariant emergent gravity modifies the normal gravitational force on galactic scales and it also gives rise to dark energy. Previous work has shown that this theory fits well on some of the existing data. One of the work-items of this project is to study in more detail whether it fits with (already existing data) of galactic rotation curves and gravitational lenses.Covariant Emergent Gravity furthermore describes a condensate at low temperature. At high temperature, however, the effects of modified gravity should fad out and go away. To understand how this happens and under exactly which circumstances, the theory must be further developed. This, too, will be done for this project.If successful, this project can deliver strong empirical evidence for the nature of dark matter, and solve a riddle that has plagued astrophysicists since the 1930s.