A theoretical physics FAQ
containing 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times (some date back to the last century), there is some overlap in the treatment of topics, and a few are a bit outdated.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
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
If you want to know my (highly nonstandard) views about the interpretation of quantum mechanics, you should read my Thermal Interpretation FAQ.
(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.
Since January 2014 there is also the Thermal Interpretation FAQ with a discussion of my own thermal interpretation of quantum mechanics.
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/additions to old topics are not indicated.
``Consider everything, and keep the good.''
(St. Paul, 1 Thess. 5:21)
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.
Part A: Quantum mechanics and its interpretation
(9 chapters with 115 sections [116 titles, two repeated in several chapters])
Chapter A2: Classical mechanics and quantum mechanics
See also my tutorial paper Phenomenological thermodynamics.
Chapter A4: The interpretation of quantum mechanics
For my own thermal interpretation of quantum mechanics, see the Thermal Interpretation FAQ
Chapter A8: Virtual particles and vacuum fluctuations
see also my thorough discussion of real and virtual particles in an answer to the question ''Are W & Z bosons virtual or not?''
Part B: Relativistic quantum mechanics and quantum field theory
(8 chapters with 84 sections)
Chapter B5: Divergences and renormalization
See also my tutorial paper Renormalization without infinities - a tutorial, which discusses renormalization on a much simpler level than quantum field theory.
Part C: Various topics
(6 chapters with 41 sections)
Since March 1, 2005, there is also a related FAQ in German language,
Arnold Neumaier (Arnold.Neumaier@univie.ac.at)