A theoretical physics FAQ

This theoretical physics FAQ contains my answers to questions on theoretical physics discussed over a number of years in various physics discussion groups (see the Acknowledgments at the end of this page).

Most topics are related to quantum mechanics, quantum field theory, renormalization, the measurement problem, randomness, and philosophical issues in physics. Since different sections were written at different times (some date back to the last century), there is some overlap in the treatment of topics, and a few are a bit outdated.

The FAQ is located at http://www.mat.univie.ac.at/~neum/physfaq/physics-faq.html

There is also a related FAQ in the German language,

Please ask questions related to the FAQ at Physics Overflow.

If you spot errors or have suggestions for improvements, please write me (at Arnold.Neumaier@univie.ac.at).

If you like the FAQ and/or found it useful, please link to it from your home page to make it more widely known.

If you found this FAQ useful you are likely to benefit also from reading the free online book

Arnold Neumaier and Dennis Westra,

Classical and Quantum Mechanics via Lie algebras,

2008, 2011. https://arxiv.org/abs/0810.1019



The thermal interpretation of quantum physics features my recent book

A. Neumaier,

Coherent Quantum Physics: A Reinterpretation of the Tradition,

de Gruyter, Berlin 2019.



Happy Reading!

Arnold Neumaier (University of Vienna)



Very little is said about the more speculative sides of theoretical physics, such as string theory, quantum gravity, and other physics beyond the standard model.

On topics where the physics community has not yet reached a consensus my point of view is of course only one of the possibilities, and usually (but not always) the mainstream view. But I tend to discuss also important alternative views. In particular, I broadly discuss various approaches to the foundations of quantum mechanics.

Abbreviations:

QM = quantum mechanics,

QFT = quantum field theory,

QED = quantum electrodynamics,

CCR = canonical commutation relations,

s.p.r. = sci.physics.research (newsgroup).

Strings like quant-ph/0303047 or arXiv:0810.1019 refer to electronic documents in the e-Print archive.

p_0 and \p (the backslash indicates a boldface font) denote the time and space part of a 4-vector p.

The Minkowski inner product is always taken to be p^2=p_0^2-\p^2.

A * indicates a new topic added (or an old one significantly expanded) since January 1, 2016.

Minor changes or additions to old topics are not indicated.

``Consider everything, and keep the good.''

(St. Paul, 1 Thess. 5:21)

Table of Contents

The various topics of this FAQ are arranged into chapters of loosely related topics. But the individual topics can usually be read independently of each other.

Labels and arrangement of the topics changed with time, and may change again as answers to further questions will be added and old answers regrouped. So, to cite part of the FAQ, refer to the title of a chapter or section and not only to its label.

Originally, all contributions to the FAQ were written in a simple text format. I am gradually converting the entries into html format. But converting an entry takes time, since the conversion must be done manually to be more legible than the original. If you'd like to have just one or two entries converted, please write me (at Arnold.Neumaier@univie.ac.at), indicating the wanted entries. This will change my editing priorities. Or, even better, do the conversion for me and send me the corresponding html file. I'll then insert it here in place of the text file, possibly after further editing to polish it a bit.

A Polish trannslation of this table of content (version of May 2, 2015) is here.

Part A: Quantum mechanics and its interpretation

(9 chapters with 115 sections [116 titles, two repeated in several chapters])

Part B: Relativistic quantum mechanics and quantum field theory

(8 chapters with 84 sections)

Part C: Various topics



(6 chapters with 41 sections)



































































































































































































