The Cosmology of the Early and Late Universe

在我们生活的宇宙中，遥远的星系正在相互加速，但原因不可能是其中存在的普通物质，因为宇宙应该在引力对其所含物质的吸引力下减速。无论导致这种加速的是什么，一定是一种我们以前在自然界中从未遇到过的新物质，我们称之为暗能量（DE）。宇宙常数（CC）是这个问题的最佳候选者，然而，今天不可能有太多的宇宙常数，因为如果有的话，它会导致星系在现在分崩离析。问题是如何将观察到的DE量与以CC形式出现的预测量相协调。后者要高得多，调和这一点多年来一直是个问题。最近，我们提出了一个解决CC被取消问题的方案，有效地消除了CC。我们打算发展我们对解决这个问题所涉及的机制的理解，并确定它是否可以在我们宇宙的粒子理论模型中被发现。这留下了DE本质是什么的问题，我们将致力于提出的模型来解释这个问题，在这个模型中，驱动加速度的力在高密度区域被屏蔽，比如在地球上。这样的模型很难排除，但我们已经建立了它们的一些特征，这将使我们能够在实验室和银河系尺度上对它们进行测试。对于相对论驱动宇宙加速的观点还有另一种观点，那就是在大尺度上，我们需要修改爱因斯坦的广义相对论（GR）。这是一个很大的企业领域，我们大量参与了对GR进行修改的模型的工作。我们将在巨大的宇宙尺度上测试其中的许多模型，并观察它们如何影响中子星等大质量物体的形成。我们还将限制暗物质的模型，暗物质是宇宙中保持星系在一起的关键成分。我们还没有发现DM到底是什么，我们的目标之一是帮助发现将我们的星系结合在一起的神秘粒子。我们将测试它是在早期宇宙中形成的原始黑洞的形式，还是一种极轻的粒子，叫做轴子。许多人认为，早期的宇宙在短暂的时间内经历了一段几乎呈指数级的膨胀，即暴胀。我们将研究暴胀模型，以确定是否可以在弦理论中找到成功的模型，这一点最近受到了许多人的质疑。我们还会问，宇宙是如何确定其中的物质多于反物质的，这就是所谓的重子生成。诺丁汉大学最近出现了一个新领域那就是通过模拟实验在实验室里测试重力理论的可能性。尽管它们的能量尺度与早期宇宙完全不同，但它们的方程相似，因此我们希望通过做这样的实验，我们可以模拟早期宇宙的效应，甚至利用结果来预测早期宇宙的时刻。我们在诺丁汉首次开发的另一个领域是利用机器学习的力量来创建神经网络来分析数据。我们希望将这项新技术应用于寻找宇宙弦、暗能量，并提供分析天文数据的新方法。这非常令人兴奋。在《量子引力》一书中，我们试图建立广义相对论和量子力学之间的联系。我们正在开发宇宙学模型，使我们能够讨论宇宙中最早的时刻，量子力学的作用至关重要，我们打算开发方法，用天文学数据来约束和测试这些模型，比如在大爆炸相关的热辐射中看到的波动。

We live in a Universe in which distant galaxies are accelerating apart from one another, but the cause for this can not be the ordinary matter present in it as the universe should be slowing down due to the attractive pull of gravity on the matter it contains. Whatever is causing this acceleration must be a new substance that we have not come across before in nature, we call it Dark energy (DE). The best candidate for this is the Cosmological Constant (CC), however, there can't be much of it around today because if there was, it would have caused galaxies to blow apart by now. The problem is reconciling the observed amount of DE with the predicted amount that should be present in the form of a CC. The latter is much higher and reconciling this has been a problem for many years. Recently, we proposed a resolution to the problem in which the CC is cancelled, effectively removing it. We intend to develop our understanding of the mechanism involved in resolving this problem and establish whether it can be found to exist in particle theory models of our Universe. This leaves open the question of what is the nature of DE and we will be working on models proposed to account for this in which the force driving the acceleration is screened from view in regions of high density such as here on Earth. Such models are hard to rule out, but we have established a number of features they have that would allow us to test for them in the laboratory and on galactic scales. There is an alternative point of view to DE driving the acceleration of our universe, and that is that on large scales we need to modify Einstein's General Theory of Relativity (GR). This is a big field of enterprise and we are heavily involved in working on models in which GR is modified. We will be testing many of these models, both on vast cosmological scales and by seeing how they effect the formation of massive objects like neutron stars. We will also constrain models of Dark Matter, the key component of the universe which keeps galaxies together. We have yet to find out what DM really is, and one of our aims is to help uncover the mysterious particle that is binding our galaxy together. We will test whether it can be in the form of primordial black holes formed in the early universe or maybe as an extremely light particle called the axion. Many people think the early Universe underwent a period of almost exponential expansion for a brief period of time, known as Inflation. We will work on models of inflation to establish whether or not successful models can be found in string theory, something that has recently been questioned by many. We will also ask how did the universe establish that there was more matter than antimatter in it, something known as Baryogenesis.A new area which has emerged here at Nottingham recently is the possibility of testing theories of gravity in the laboratory by creating analogue experiments. Although at a completely different energy scale to the early universe, they enjoy similar equations, hence the hope that by doing such experiments we can mimc early universe effects and even use the results to make predictions about those earliest moments. Another area we are developing at Nottingham for the first time is to use the power of Machine Learning to create neural networks to analyse data. We are hoping to apply this new technology to search for cosmic strings, dark energy and provide new ways to analyse astronomical data. It is very exciting. In Quantum Gravity, we attempt to establish a connection between General Relativity and Quantum Mechanics. We are developing models of cosmology that allow us to talk about the earliest moments in the universe where the role of Quantum Mechanics is vital and intend to develop methods to constrain and test these models with astronomical data such as the fluctuations seen in the thermal radiation associated with the Big Bang.