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# 物理代写|费曼图代写Feynman Diagram代考|PHYSICS7013 Correct and Justified Predictions

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## 物理代写|费曼图代写Feynman Diagram代考|Correct and Justified Predictions

Weinberg (1995, p. 38$)$ writes that “the missing element was confidence in renormalization as a means of dealing with infinities”, and puts forward the absence of trustworthy experimental data as the principal reason for this lack of confidence. J. Robert Oppenheimer, in his contribution to the Solvay Congress in 1948, that is when QED was in transition, was of the same opinion. In order to explain why the Lamb shift was not correctly predicted earlier, he remarks:
In their application to level shifts, these developments, which could have been carried out at any time during the last fifteen years, required the impetus of experiment to stimulate and verify. (Oppenheimer 1950, p. 271, reprinted in Schwinger 1958, p. 146)
Weinberg (1995, pp. 37-38) points out that experimental evidence for the level shifts mentioned by Oppenheimer was already available at the end of the $1930 \mathrm{~s}^{20}$ However, the results only became reliable through the experiments of Willis Lamb and his collaborators. ${ }^{21}$ The measured level shifts deviated from the values predicted by the old theory of QED that was based on Dirac’s equation. Another deviation from Dirac’s theory was encountered in the magnetic moment of the electron. ${ }^{22}$ Using the renormalization of mass and charge, which characterizes modern QED, these values could now be accounted for. ${ }^{23}$

However, the fit between theoretical predictions and reliable experimental data does not completely justify the theory. Wolfgang Pauli, for one, is more concerned with other types of justification for renormalization:
Even if one claims relativistic invariance and finiteness of the results this alone is not sufficient to make the subtraction-rules unique. One has to search for additional physical point of views. $[\ldots]$ The problem seems to be more to make the applied rules plausible and unique. (Pauli to Rabi, 15 January 1948, letter 931 in Pauli, Hermann and Meyenn 1979)
Dancoff (1939, p. 963), who was, according to the accounts mentioned above, only a calculational error away from the modern findings, tells the reader of “the fortuitous nature” of his results!

## 物理代写|费曼图代写Feynman Diagram代考|Representing and Calculating

That Feynman diagrams were characterized as being the chief tool in quantum electrodynamic calculations and that physicists warned others of incorrectly interpreting them as representing the trajectories of particles and, even worse, of particles in intermediate states, have been thoroughly examined. However, the inference from these observations that organizing calculations is the only function of the diagrams and that they cannot be consistently interpreted as representing physical processes is not sound. Diagrams can function simultaneously as idealized representations of the phenomena under study and as a tool for deriving statements about these phenomena.

Meynell (2008) elucidates the problem of representation in the case of Feynman diagrams by discussing accounts of different forms of representation mainly from the fields of aesthetics and the history of art, for example those of Goodman (1968) and Kendall Walton (1990). She also argues that the diagrams’ function as a computational device does not preclude them from also being representations.

Familiar examples from the field of classical mechanics can act as cases in point, such as the graphical representation of a massive body on an inclined plane (see Fig. 1.2). Here, the abstract drawing serves to articulate the relevant aspects of the physical situation and, at the same time, to derive relationships between the vector of forces acting on the sliding object. As far as their principal functions are concerned, Feynman diagrams are no different.

Quantitative results are not always derived from the mathematical formulae obtained from the relations illustrated in the diagrams. At times the derivations are conducted directly by means of the diagrams. In her study on Venn diagrams, SunJoo Shin (1994) writes that diagrams can provide the means by which statements can be derived from other statements just as well as formulae. The representation of positrons in an early stage of the development of Feynman diagrams is an example of a proof conducted, to a large extent, directly by diagrams (see Section 4.6.2) in which Feynman performs what I like to call a diagrammatic induction. For another instance of diagrammatic induction, using a more familiar example, see Appendix A.

## 物理代写|费曼图代写Feynman Diagram代考|Correct and Justified Predictions

Weinberg (1995, pp. 37-38) 指出 Oppenheimer 提到的能级偏移的实验证据在1930 s20然而，只有通过威利斯·兰姆和他的合作者的实验，结果才变得可靠。21测得的电平位移偏离了基于狄拉克方程的旧 QED 理论预测的值。另一个偏离狄拉克理论的地方是电子的磁矩。22使用现代 QED 特征的质量和电荷的重整化，现在可以解释这些值。23

(1939, p. 963)，根据上面提到的叙述，与现代研究结果相距仅一个计算错误，他告诉他的结果的“偶然性”的读者！

## 物理代写|费曼图代写Feynman Diagram代考|Representing and Calculating

Meynell (2008) 通过讨论主要来自美学和艺术史领域的不同表示形式的描述，例如 Goodman (1968) 和 Kendall Walton (1990)，阐明了费曼图的表示问题。她还认为，图表作为计算设备的功能并不排除它们也可以作为表示。

## 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。