物理代写|宇宙学代写cosmology代考|Black Holes, Cosmology and Extra Dimensions

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宇宙学是天文学的一个分支,涉及宇宙的起源和演变,从大爆炸到今天,再到未来。宇宙学的定义是 “对整个宇宙的大尺度特性进行科学研究”。

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我们提供的宇宙学cosmology及其相关学科的代写,服务范围广, 其中包括但不限于:

  • Statistical Inference 统计推断
  • Statistical Computing 统计计算
  • Advanced Probability Theory 高等概率论
  • Advanced Mathematical Statistics 高等数理统计学
  • (Generalized) Linear Models 广义线性模型
  • Statistical Machine Learning 统计机器学习
  • Longitudinal Data Analysis 纵向数据分析
  • Foundations of Data Science 数据科学基础
物理代写|宇宙学代写cosmology代考|Black Holes, Cosmology and Extra Dimensions

物理代写|宇宙学代写cosmology代考|Einstein after Einstein

But let us again avoid “running ahead of the engine” and return to the 20 s and 30 s of last century. It was the time of physics’ active penetration into the micro-world and formation of a language adequate to its properties – quantum mechanics, later quantum electrodynamics and, wider, quantum field theory. The quantum theory was first built in the framework of the old, Newtonian concepts of absolute time and absolute space (nonrelativistic quantum mechanics), and it required substantial effort to extend it to the world of large velocities and high energies and to formulate its content in Minkowski’s four-dimensional space-time.

The understanding of gravity as space-time curvature endowed GR with an exclusive character as compared to all the rest of physics, and this was in conflict with the feeling of unity of the material world, important for both philosophers and physicists. On the other hand, in GR itself there emerge quite a number of important problems, one of which is known as the problem of energy. The notions of energy and other conserved quantities play a very significant part in the structure of quantum theory. In flat space, one easily formulates the energy, momentum and angular moment conservation laws due to the symmetry of Minkowski space with respect to temporal and spatial translations and rotations, forming the 10 -parameter Poincaré group. In curved space-time there are no such symmetries at all, and it is therefore quite difficult to define the energy and momentum of the gravitational field in GR in a consistent way.

For this and some other reasons, not all physicists have agreed with GR, and even now there are repeated attempts to build a theory of gravity in Minkowski space. Unlike the first attempts of this kind, the new authors have learned to explain the classical observed effects of GR, and gravitation in such theories is represented by a field with normal conservation laws and hopes to be quantized on equal grounds with other physical fields. According to Will’s book [563], as early as in 1960 the number of such theories exceeded 25. But neither then nor afterwards did such theories give rise to really substantial interest (though certainly their followers would not agree with such a conclusion).

物理代写|宇宙学代写cosmology代考|The technological breakthrough

By the end of the 1950 s, physics already knew four rather than two basic interactions: the gravitational, electromagnetic, strong nuclear (due to which protons and neutrons join to form atomic nuclei) and weak nuclear (which is responsible for many particle transmutations and nuclear reactions of which the most well-known is beta decay). Among them, the gravitational interaction appeared to be something of minor importance: for particles, being much weaker than even the weak interaction, it seemed absolutely insignificant in micro-world physics. The accelerators supplied more and more new experimental data about the other three interactions, and quantum field theory in flat Minkowski space experienced rapid progress, formulating and solving various problems of particle physics. Against such a background, gravitational studies seemed to be something of extravagance. Yes, GR was recognized as a fundamental, almost philosophical theory, important for the world outlook, but its experimental basis was too poor: one effect, Mercury’s perihelion advance, was checked up to $1 \%$, and another, light bending near the Sun, up to roughly $30 \%$. The cosmological observations could only testify to a nontrivial geometry of the Universe but could tell us nothing about the validity of particular gravitational equations… Kip Thorne, at that time a student and now one of the most famous gravitational physicists, was advised by his professors not to deal with GR, which, in their opinion, was a theory very weakly connected with the rest of physics and astronomy. He did not obey such an advice and, as far as we can guess, hardly regrets now.

物理代写|宇宙学代写cosmology代考|To quantize or not

As already pointed out, the experiment entirely supports GR. However, the picture is not so unclouded in theory. We have previously mentioned the gravitational energy problem. Another well-known difficulty of GR is the existence of singularities which emerge in the majority of exact solutions to the Einstein equations and, in particular, they are hidden beyond black hole horizons and occur at the beginning and, in some models, at the end of the cosmological evolution as well as in modeling isolated bodies. These are, to put it simply, the points, lines or surfaces where the space-time loses smoothness and the quantities characterizing the curvature become either indefinite or infinite. Singularities may be connected with infinite matter densities or pressures, but there also exist purely geometric singularities, such as those in solutions to the Einstein equations in vacuum, in the absence of any matter. The inevitability of singularities in GR solutions has been proved under very general and reasonable conditions in a number of theorems, and this clearly indicates that GR is apparently not very precise in its description of extremely strong gravitational fields.

Unlike event horizons, i.e., black hole boundaries (distinguished but quite regular surfaces that work according to the remarkable principle “everybody can come in, nobody can go out”), singularities represent a real problem for the theory since they indicate, on the

basis of the theory itself, the places where it does not work any more. Thus GR itself prompts to the necessity of going out of its own framework. How to do that? It is a question of great importance, the subject of many studies and discussion, maybe a question outside the framework of not only gravitation theory but physics as a whole.
It seems natural, for example, to try to account for quantum phenomena.

物理代写|宇宙学代写cosmology代考|Black Holes, Cosmology and Extra Dimensions


物理代写|宇宙学代写cosmology代考|Einstein after Einstein


将引力理解为时空曲率,赋予了地球物理学与其他所有物理学相比的独特性,这与物质世界的统一感相冲突,这对哲学家和物理学家都很重要。另一方面,在 GR 本身中也出现了许多重要的问题,其中一个就是众所周知的能源问题。能量和其他守恒量的概念在量子理论的结构中起着非常重要的作用。在平面空间中,由于 Minkowski 空间关于时空平移和旋转的对称性,人们很容易制定能量、动量和角矩守恒定律,形成 10 参数 Poincaré 群。在弯曲的时空中根本没有这样的对称性,

由于这个和其他一些原因,并不是所有的物理学家都同意 GR,即使是现在也有反复尝试在 Minkowski 空间中建立引力理论。与第一次尝试不同的是,新作者已经学会了解释 GR 的经典观测效应,并且这种理论中的引力由具有正常守恒定律的场表示,并希望在与其他物理场相同的基础上进行量化。根据威尔的书[563],早在 1960 年,此类理论的数量就超过了 25 个。但无论是当时还是之后,这些理论都没有引起真正的实质性兴趣(尽管他们的追随者肯定不会同意这样的结论)。

物理代写|宇宙学代写cosmology代考|The technological breakthrough

到 1950 年代末,物理学已经知道四种而不是两种基本相互作用:引力、电磁、强核(由于质子和中子结合形成原子核)和弱核(负责许多粒子嬗变和其中最著名的核反应是β衰变)。其中,引力相互作用似乎是次要的:对于粒子来说,比弱相互作用还要弱得多,在微观世界物理学中似乎绝对微不足道。加速器为其他三种相互作用提供了越来越多的新实验数据,平面闵可夫斯基空间的量子场论取得了飞速发展,制定并解决了粒子物理学的各种问题。在这样的背景下,引力研究似乎有些奢侈。是的,GR被认为是一种基本的,几乎是哲学的理论,对世界观很重要,但它的实验基础太差了:一个效应,水星近日点推进,被检查到1%,以及另一个,太阳附近的光弯曲,大约30%. 宇宙学观察只能证明宇宙的非平凡几何,但不能告诉我们有关特定引力方程的有效性……基普索恩,当时是一名学生,现在是最著名的引力物理学家之一,他的教授们建议他不要处理 GR,在他们看来,这是一个与物理学和天文学的其余部分联系非常薄弱的​​理论。他没有听从这样的建议,据我们猜测,他现在几乎不后悔。

物理代写|宇宙学代写cosmology代考|To quantize or not

正如已经指出的,该实验完全支持 GR。然而,从理论上讲,情况并非如此明朗。我们之前提到过引力能问题。GR 的另一个众所周知的困难是奇点的存在,这些奇点出现在爱因斯坦方程的大多数精确解中,特别是它们隐藏在黑洞视界之外,并且在开始时出现,在某些模型中,在结束时出现宇宙学演化以及孤立物体的建模。简而言之,就是时空失去平滑性的点、线或面,表征曲率的量变得不确定或无限。奇点可能与无限的物质密度或压力有关,但也存在纯几何奇点,例如在没有任何物质的情况下,爱因斯坦方程在真空中的解。许多定理在非常普遍和合理的条件下证明了 GR 解中奇点的必然性,这清楚地表明 GR 对极强引力场的描述显然不是很精确。


理论本身的基础,它不再起作用的地方。因此,GR 本身提示了走出自己的框架的必要性。怎么做?这是一个非常重要的问题,是许多研究和讨论的主题,可能不仅是引力理论,而且是整个物理学框架之外的问题。

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术语 广义线性模型(GLM)通常是指给定连续和/或分类预测因素的连续响应变量的常规线性回归模型。它包括多元线性回归,以及方差分析和方差分析(仅含固定效应)。



有限元是一种通用的数值方法,用于解决两个或三个空间变量的偏微分方程(即一些边界值问题)。为了解决一个问题,有限元将一个大系统细分为更小、更简单的部分,称为有限元。这是通过在空间维度上的特定空间离散化来实现的,它是通过构建对象的网格来实现的:用于求解的数值域,它有有限数量的点。边界值问题的有限元方法表述最终导致一个代数方程组。该方法在域上对未知函数进行逼近。[1] 然后将模拟这些有限元的简单方程组合成一个更大的方程系统,以模拟整个问题。然后,有限元通过变化微积分使相关的误差函数最小化来逼近一个解决方案。





随机过程,是依赖于参数的一组随机变量的全体,参数通常是时间。 随机变量是随机现象的数量表现,其时间序列是一组按照时间发生先后顺序进行排列的数据点序列。通常一组时间序列的时间间隔为一恒定值(如1秒,5分钟,12小时,7天,1年),因此时间序列可以作为离散时间数据进行分析处理。研究时间序列数据的意义在于现实中,往往需要研究某个事物其随时间发展变化的规律。这就需要通过研究该事物过去发展的历史记录,以得到其自身发展的规律。


多元回归分析渐进(Multiple Regression Analysis Asymptotics)属于计量经济学领域,主要是一种数学上的统计分析方法,可以分析复杂情况下各影响因素的数学关系,在自然科学、社会和经济学等多个领域内应用广泛。


MATLAB 是一种用于技术计算的高性能语言。它将计算、可视化和编程集成在一个易于使用的环境中,其中问题和解决方案以熟悉的数学符号表示。典型用途包括:数学和计算算法开发建模、仿真和原型制作数据分析、探索和可视化科学和工程图形应用程序开发,包括图形用户界面构建MATLAB 是一个交互式系统,其基本数据元素是一个不需要维度的数组。这使您可以解决许多技术计算问题,尤其是那些具有矩阵和向量公式的问题,而只需用 C 或 Fortran 等标量非交互式语言编写程序所需的时间的一小部分。MATLAB 名称代表矩阵实验室。MATLAB 最初的编写目的是提供对由 LINPACK 和 EISPACK 项目开发的矩阵软件的轻松访问,这两个项目共同代表了矩阵计算软件的最新技术。MATLAB 经过多年的发展,得到了许多用户的投入。在大学环境中,它是数学、工程和科学入门和高级课程的标准教学工具。在工业领域,MATLAB 是高效研究、开发和分析的首选工具。MATLAB 具有一系列称为工具箱的特定于应用程序的解决方案。对于大多数 MATLAB 用户来说非常重要,工具箱允许您学习应用专业技术。工具箱是 MATLAB 函数(M 文件)的综合集合,可扩展 MATLAB 环境以解决特定类别的问题。可用工具箱的领域包括信号处理、控制系统、神经网络、模糊逻辑、小波、仿真等。



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