The bright and the dark Universe - from bright stars to Dark Energy

天文学是一门奇妙的科学。我们没有传统的实验室供我们使用，我们不能戳戳我们的科学对象，我们也不能设置精心设计的实验来最好地检验我们的科学假设。我们的实验室就是宇宙——从附近的恒星和行星到遥远的星系；我们的仪器是望远镜，收集各种波长的光，精确定位发光的恒星、气体和星系的位置。我们的实验是巧妙地对这些物体进行观察，将它们发出的光转化为有关它们组成的信息，在我们认为是它们进化的不同阶段研究它们，并观察它们对邻近物体的影响。我们在宇宙这个极其混乱的主实验室里创造我们自己的实验，我们接受挑战，解释它是如何产生的，它是由什么组成的，它将如何结束，以及是什么基本定律使整个事物运转起来。考虑到我们已经了解到的一些情况，我们很擅长这一点：宇宙大约有137亿年的历史，而且它一直在膨胀；它的扩张似乎正在加速；宇宙中充满了各种大小、形状和颜色的令人愉快的星系组合；星系中充满了恒星、行星、气体和尘埃；宇宙中似乎充满了一种看不见的神秘物质，它们只对宇宙的四种基本力有一种反应：引力。然而，作为一名科学家，我的重点是我们还不知道的事情。为什么宇宙在加速膨胀（我们称之为暗能量的现象）？它是由一种以前未知的力量驱动的，还是宇宙的加速是一种错觉，源于对引力如何起作用的潜在缺乏理解？为什么宇宙中的大部分物质是看不见的？暗物质与宇宙中可见的物质含量有什么关系？它又如何影响宇宙的演化？为什么会有如此多的星系？为什么有些是蓝色、红色或绿色，它们与宇宙中看不见的物质分布有什么关系？对于回答这些基本问题的艰巨任务，我个人的贡献是在可见和不可见的宇宙组成部分之间建立起牢固的联系。作为欧内斯特卢瑟福研究员，我将首先了解我们如何自信地解释来自星系的光，以一种告诉我们它们自身的生长和演化的方式，然后如何将其与宇宙中占主导地位的暗物质成分的演化联系起来。为了做到这一点，我将采用恒星光的模型和宇宙中结构在重力作用下如何增长的模型，并首次将这些模型与观测和计算机模拟以一种自一致的方式进行对比。结果将是增加对某些类型的星系与暗物质之间关系的了解，反过来，这些知识将使我能够选择最佳的观测集来了解宇宙结构是如何形成的。这是一项艰巨的任务，但我已经在初步分析中表明，我们获得的知识为理解暗能量在宇宙时间的行为迈出了一大步，并增强了我们对引力的认识。换句话说，我的研究计划是一项雄心勃勃的优化工作。它将我们对宇宙的有限观察转化为研究其基本规律的有力工具，同时了解宇宙中我们有幸观测到的美丽部分——星系。

Astronomy is a curious science. We have no traditional laboratories at our disposal, we cannot poke and prod our scientific subjects, nor can we setup carefully thought out experiments that will best test our scientific hypotheses. Our laboratory is the Universe - from nearby stars and planets to astronomically distant galaxies; our instruments are telescopes, gathering light of all wavelengths, pinpointing the position of shining stars, gas and galaxies. Our experiments are cleverly selected observations of these objects, translating their light into information about their composition, studying them at what we believe are different stages of their evolution, and observing their effect on neighbouring objects. We create our own experiments from the immensely chaotic master laboratory that is the Universe, and we take on the challenge that is to explain how it came to be, what it is made of, how it will end, and what fundamental laws tick the whole thing into motion.We are good at this, consider some of what we have learned: that the Universe is around 13.7 billion years old and that it has since been expanding; that its expansion is seemingly accelerating; that the Universe is full of a delightful mix of galaxies of all sizes, shapes and colours; that galaxies are filled with stars, planets, gas and dust; and that the Universe seems filled with a mysterious unseen amount of matter that responds only one to the four fundamental forces of the Universe: gravity. As a scientist, however, my focus is firmly on things we do not yet know. Why is the expansion of the Universe accelerating (a phenomenon we call Dark Energy)? Is it being driven by a force previously unknown, or is the Universe's acceleration an illusion that stems from a potential lack of understanding of how gravity works? How come most of the matter of the Universe is unseen? How does this Dark Matter relate to the visible tip of the Universe's matter content, and how does it affect its evolution? And why such a variety of galaxies? Why some blue, red or green, and how do they relate to the unseen matter distribution of the Universe?My personal contribution towards the monumental task that is answering these fundamental questions is to establish a robust link between the components of the Universe that are visible and those that are not. As an Ernest Rutherford Fellow I will begin by understanding how we can confidently interpret the light coming from galaxies in a way that tells us about their own growth and evolution, and then how to link it to the evolution of the dominating Dark Matter component of the Universe. I will do this by taking both models of stellar light and models of how structure grows in the Universe under the force of gravity and, for the first time, contrasting such models with observations and computer simulations in a self-consistent way. The result will be an increased knowledge of how certain types of galaxies relate to the Dark Matter, and in turn this knowledge will allow me to select the optimal set of observations to learn how structure formed in the Universe. This is a tough task, but I have shown in a preliminary analysis that the knowledge we gain provides a big step in understanding the behaviour of Dark Energy across cosmic times, and enhances our knowledge about gravity.In other words, my research programme is an ambitious optimisation exercise. One that turns the limited observations we can make of the Universe into as powerful tool to investigate its fundamental laws as possible, whilst simultaneously learning about the beautiful part of the Universe that we are luck enough to observe - galaxies.