Posted on Categories:General Relativity, 广义相对论, 物理代写

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## 物理代写|广义相对论代写General Relativity代考|Relativistic Units

Relativistic Units. Because the speed of light $c$ is frame-independent, we can connect space and time units in a frame-independent way. The nearly universal convention in general relativity is to express both distance and time in units of meters (rather than in seconds), where we define a meter of time to be the time it takes light to travel a meter of distance. Since light travels $299,792,458 \mathrm{~m}$ in $1 \mathrm{~s}$ (by definition of the SI meter), a meter of time is $1 / 299,792,458 \mathrm{~s}=3.34 \mathrm{~ns}$.

Light moves at a speed of $1 \mathrm{~m} / \mathrm{m}=1$ by definition in this unit system, so all other velocities are expressed as unitless fractions of the speed of light. This implies that mass $m$, momentum (which must have the same units as $m v$ ), and energy (which must have the same units as $\frac{1}{2} m v^2$ ) all have the same units. For macroscopic objects, I will use the SI kilogram as the common unit for these quantities, but for microscopic objects (molecules and smaller), I will use the electron volt (eV).

Let us call the unit system where time and distance are measured in meters and mass, momentum, and energy are measured in kilograms the GR (General Relativistic) unit system. See box $2.2$ for conversion factors between SI and GR units.

## 物理代写|广义相对论代写General Relativity代考|Clock Synchronization

Clock Synchronization. If the time coordinates assigned by the clocks in a reference frame of the type shown in figure $2.1$ are to have any coherent meaning, the clocks must be synchronized. Since the speed of light $c=1 \mathrm{~m} / \mathrm{m}=1$ must have the same value in all IRFs (as argued a few paragraphs back), these clocks will be synchronized if and only if an observer concludes that the speed of a light flash traveling between any pair of clocks is 1. This means that if a master clock emits a light flash at time $t$, a clock a distance $d$ from the master will be correctly synchronized with it if it reads time $t+d$ when a signal passes. This provides a straightforward method for synchronizing the clocks in an inertial frame.
(Note that this method does not work in NIRFs, so we will have to use a different approach to assigning events coherent time coordinates in general relativity.)

## 物理代写|广义相对论代写广义相对论代考|时钟同步

(注意这个方法在nirf中不起作用，所以我们将不得不使用不同的方法来分配广义相对论中的事件相干时间坐标。

## 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。