Local Universe tests of gravity and dark energy

21世纪天体物理学最令人吃惊的发现之一是宇宙的膨胀正在加速。宇宙学家针对这一挑战提出了两种可能的解释：一种被广泛接受的范式假设是，宇宙常数（真空能量）推动宇宙加速膨胀。尽管这一理论在科学界被广泛接受，但没有人知道所谓的“暗能量”的真正物理性质。一个更非正统的观点是，万有引力定律——广义相对论——可能在大尺度上被修正。在这个项目中，我们的目标是通过非常详细地研究局部宇宙的形成来测试后者，并将局部宇宙作为研究引力和暗能量本质的宇宙实验室。具体来说，我们的目标是对局部宇宙进行有约束的模拟，假设两种假设，但重点关注引力变化的影响，努力提供新的独立方法来排除一种存在或不存在。约束模拟是对结构形成的宇宙学模拟，其中初始条件受到观测数据的约束，因此最终结果注定要再现观测到的宇宙景观。这样的模拟可以让宇宙学家直接模拟银河系和本星系群的环境，而不是模拟随机的统计上相似的结构。德国方面在运行和分析此类模拟方面处于世界领先地位，而波兰方面在测试修正重力理论方面处于世界领先地位。通过结合我们的专业知识，我们将第一次能够在广义相对论的假设下建立局部宇宙的模型，广义相对论是现代物理学的基础之一，在一个多世纪以来一直处于主导地位，只是在小尺度上揭示的自然的近似值。我们的项目将在星系和结构形成领域（解决本地群体和本地宇宙如何形成的问题）以及在修正重力领域中产生重大影响，这些修正重力排除了文献中提出的特定模型。我们合作的价值是显而易见的：只有结合我们互补的专业知识，这样的研究才有可能。此外，由于我们的专业知识是如此互补，我们设想在波兰和德国方面之间进行持久的知识转移，德国方面在修正重力方面获得永久的专业知识，波兰方面成为受限模拟的参与者。总而言之，这个项目——LUSTRE（引力和暗能量的局部宇宙测试）——旨在利用局部宇宙作为宇宙实验室来探索广义相对论和宇宙加速的基本物理。

One of the most startling discoveries of 21st century astrophysics is that the expansion of the universe is accelerating. Cosmologists have zeroed in on two possible explanations for this challenge: the widely accepted paradigmatic hypothesis is that a cosmological constant (vacuum energy) drives the universe towards increasing its rate of expansion. Despite wide acceptance of this theory in the community, no one knows the true physical nature of the so called “dark energy".A more unorthodox notion is that the law of gravity — general relativity — may be modified on large scales. In this project we aim to test the latter by studying in great detail the formation of the local universe and to use the local universe as a cosmological laboratory to study the nature of gravity and dark energy.Specifically we aim to run constrained simulations of the local universe assuming both hypotheses but focusing on the effect of modifications to gravity, in an effort to provide new independent ways of ruling one in or out. Constrained simulations are cosmological simulations of structure formation where the initial conditions have been constrained by observational data, such that the final result is destined to reproduce the observed cosmographic landscape. Such simulations allow cosmologists to directly model the environment of the Milky Way and Local Group, instead of simulating random statistically similar structures. The German side is a world leader in running and analysing such simulations, while the Polish side is a world leader in testing theories of modified gravity. By combining our expertise we will, for the first time, be able to produce models of the Local Universe under the assumption that the laws of general relativity, one of the foundations of modern physics that has stood prime for over a century, are only an approximation to nature, revealed on small scales. Our project will have a major impact in both the fields of galaxy and structure formation (addressing question of how the local group and local universe formed), as well as in the field of modified gravity ruling in or out specific models that have been put forth in the literature.The value of our cooperation is straight forward: only by combing our complementary expertise is such a study possible. Furthermore because our expertise is so complementary we envision lasting knowledge transfer between the Polish and German side with the German side gaining permanent expertise in modified gravity and the Polish side becoming a player in constrained simulations.In sum, this project - LUSTRE (Local UniverSe Tests of gRavity and dark Energy) - aims at using the Local Universe as a cosmological laboratory to probe the fundamental physics of general relativity and cosmic acceleration.