### 物理代写|宇宙学代写cosmology代考|PHYC90009

statistics-lab™ 为您的留学生涯保驾护航 在代写宇宙学cosmology方面已经树立了自己的口碑, 保证靠谱, 高质且原创的统计Statistics代写服务。我们的专家在代写宇宙学cosmology代写方面经验极为丰富，各种代写宇宙学cosmology相关的作业也就用不着说。

• Statistical Inference 统计推断
• Statistical Computing 统计计算
• (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|The Invisible Universe

Most of the matter and energy in the universe is invisible. The stuff that we can see ordinary atoms – accounts for less than $5 \%$ of the total. The rest is in the form of dark matter and dark energy.

The term dark matter was coined by Fritz Zwicky in 1933. When studying galaxies in the Coma cluster, he realized that they were moving faster than expected [1]. To explain the stability of the Coma cluster he was forced to introduce an extra form of “dunkle materie.” Further evidence for the existence of dark matter came in the 1970 s when Vera Rubin and collaborators measured the rotation speeds of hydrogen gas in the outer reaches of galaxies [2]. The large speeds that they found could only be explained if these galaxies were embedded in halos of dark matter.
Today, some of the most striking evidence for dark matter comes from the gravitational lensing of the cosmic microwave background (CMB). As the CMB photons travel through the universe, they get deflected by the intervening large-scale structure. This results in a distortion of the hot and cold spots of the CMB. The effect depends on the total amount of matter in the universe and has been measured by the Planck satellite [3]. At the same time, the observed light element abundances suggest a smaller amount of ordinary baryonic matter. The mismatch between the two measurements points to the existence of non-baryonic dark matter. The same amount of dark matter is also needed to explain the rate of gravitational clustering. The small density variations observed in the early universe only grow fast enough if assisted by the presence of dark matter.

## 物理代写|宇宙学代写cosmology代考|The Hot Big Bang

The universe is expanding [7]. It was therefore denser and hotter in the past. Particles were colliding frequently and the universe was in a state of thermal equilibrium with an associated temperature $T$. It is convenient to set Boltzmann’s constant to unity, $k_{\mathrm{B}}=1$, and measure temperature in units of energy. Moreover, we will often use the particle physicists’ convention of measuring energies in electron volt $(\mathrm{eV})$ :
\begin{aligned} \mathrm{eV} & \approx 1.6 \times 10^{-19} \mathrm{~J} \ & \approx 1.2 \times 10^{4} \mathrm{~K} . \end{aligned}
For reference, typical atomic processes are measured in $\mathrm{eV}$, while the characteristic scale of nuclear reactions is $\mathrm{MeV}$. A useful relation between the temperature of the early universe and its age is
$$\frac{T}{1 \mathrm{MeV}} \simeq\left(\frac{t}{1 \mathrm{sec}}\right)^{-1 / 2}$$
One second after the Big Bang the temperature of the universe was therefore about $1 \mathrm{MeV}$ (or $10^{11} \mathrm{~K}$ ). While there was very little time available in the early universe, the rates of reactions were extremely high, so that many things happened in a short amount of time (see Table 1.2).

Above $100 \mathrm{GeV}$ (or a trillionth of a second after the Big Bang), all particles of the Standard Model were in equilibrium and were therefore present in roughly equal abundances. This state can be viewed as the initial condition for the hot Big Bang. The density at that time was a staggering $10^{36} \mathrm{~kg} \mathrm{~cm}^{-3}$, which is what you would get if you compressed the mass of the Sun to the size of a marble. In a billionth of a second, the universe expanded by a factor of 10000 . During this expansion, the temperature dropped and the universe went through different evolutionary stages.
At around $100 \mathrm{GeV}$ (or $10^{15} \mathrm{~K}$ ), the electroweak (EW) symmetry of the Standard Model was broken during the EW phase transition. The electromagnetic and weak nuclear forces became distinct entities and the matter particles received their masses. Although the basics of EW symmetry breaking are well understood-and have been experimentally verified by the discovery of the Higgs boson $[8,9]$-the detailed dynamics of the EW phase transition and its observational consequences are still a topic of active research.

## 物理代写|宇宙学代写cosmology代考|The Invisible Universe

Fritz Zwicky 在 1933 年创造了暗物质这个术语。在研究后发座星系团中的星系时，他意识到它们的移动速度比预期的要快 [1]。为了解释昏迷星团的稳定性，他被迫引入了一种额外形式的“dunkle materie”。暗物质存在的进一步证据出现在 1970 年代，当时 Vera Rubin 和合作者测量了星系外围氢气的旋转速度 [2]。只有当这些星系嵌入暗物质光晕中时，才能解释他们发现的如此大的速度。

## 物理代写|宇宙学代写cosmology代考|The Hot Big Bang

$$\mathrm{eV} \approx 1.6 \times 10^{-19} \mathrm{~J} \quad \approx 1.2 \times 10^{4} \mathrm{~K}$$

$$\frac{T}{1 \mathrm{MeV}} \simeq\left(\frac{t}{1 \mathrm{sec}}\right)^{-1 / 2}$$

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## MATLAB代写

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。