Talk:Vacuum polarization

Fock vacuum?

What's all this stuff about the Fock vacuum versus the true vacuum? Could someone who knows what this means please translate it into language understandable by a layperson? Thanks! HEL 00:10, 5 November 2006 (UTC) To clarify: Fock vacuum and true vacuum are wikilinked in the article but the corresponding pages do not exist. It would be best to give a brief explanation in this article what is meant by these terms (and maybe also create the corresponding pages!). HEL 03:58, 5 November 2006 (UTC)

"Fock vacuum" means the state with no particles. If your theory didn't allow particles to interact with each other, then you could calculate the energy of a state by simply adding up the energies of each particle. Thus, the lowest energy state would be the state with no particles: the Fock vacuum.

However, in realistic theories particles are allowed to interact. In this case it is sometimes energetically favorable for particles to exist (the energy gained from their interactions makes up for the energy cost of creating them). The lowest energy state in your interacting theory -- the "true vacuum" -- ends up being a state with virtual particles continually popping in and out of existence. -- Tim314 (talk) 06:41, 12 September 2008 (UTC)

That said, I think all this discussion of "fock vacuum" vs. "true vacuum" doesn't really belong here. It ought to go in the article on quantum field theory, or perhaps in the article on virtual particles. Including such technical terms here seems unnecessary and makes the article less accessible.

For reference, here is the text in question:

In quantum physics, if we expand about the perturbative vacuum, i.e., the ground state of the (unphysical) theory in which electrons, positrons and photons do not interact, then the true vacuum, i.e., the ground state of the interacting theory, contains short-lived "virtual" particle-antiparticle pairs which are created out of the Fock vacuum and then annihilate each other.

I have replaced it with this:

According to quantum field theory, the ground state of a theory with interacting particles is not simply empty space. Rather, it contains short-lived "virtual" particle-antiparticle pairs which are created out of the vacuum and then annihilate each other.

A reader who wants to know more about why there are virtual particles can read the articles on virtual particles and quantum field theory. -- Tim314 (talk) 07:00, 12 September 2008 (UTC)

"Theory": confusing typo?

This sentence:

According to quantum field theory, the ground state of a theory with interacting particles is not simply empty space.

(emphasis mine) seems to have a typo?

—Ruakh_TALK 14:36, 9 August 2009 (UTC)

true charge of an electron

The article states:

In the presence of an electric field, e.g., the electromagnetic field around an electron, these particle-antiparticle pairs reposition themselves, thus partially counteracting the field (a partial screening effect, a dielectric effect). The field therefore will be weaker than would be expected if the vacuum were completely empty.

If this is true then the true charge of an electron is actually a tiny amount greater than what we observe. Lemmiwinks2 (talk) 23:21, 17 October 2009 (UTC)

Yes, perturbation theory suggests it is infinitely greater, see renormalisation. Xxanthippe (talk) 04:09, 21 November 2009 (UTC).

A description of Vacuum Polarization from 1922

"The substances perceived to us are atoms which come into existence from vacuity and drop out of existence again. Thus when a body moves from one position to another the atoms in the first position cease to be and a group of new similar atoms comes into existence in the second position, so the movement involves a series of annihilations and creations"

De Lacy O'Leary, 1922

Before mentioning the title of the book, I must say that's a very accurate description especially since quantum mechanics wasn't born yet. It can be understood why the author used some of the less accurate terms because, well without QM, there were no better choices at the time.

Now the odd thing is the title of the book "Arabic Though and It's Place in History" in the Chapter "Orthodox Scholasticism". The author was translating religions ideas for western readers using scientific terms. Which must be emphasized the concept did not exist in western science at that time, so he did an impressive job with what he had to work with. The author therefore is in a sense the first westerner to describe the phenomena far ahead of the physics people (me being one of them). Of course the field, polarization, and all those terms were not even theory in 1922, so he did an amazing job all things considered.

The next sentence is "The cause of these changes is God, the only permanent and absolute reality" which is natural considering that happens to be what he was writing about in the book.

The use of western scientific context is impressive in accuracy and seems odd for a book on Arabic thought, where some Greek Philosophical parallels would have seem to be the choice. Fx303 (talk) 05:31, 24 October 2009 (UTC)

Derivation uses confusing sentence structure

For example:

"Maxwell's equations are the classical limit of the quantum electrodynamics which cannot be described by any classical theory. A point charge must be modified at extremely small distances less than the reduced Compton wavelength λ c {\displaystyle {\lambda _{c}}} {\displaystyle {\lambda _{c}}} ( = ℏ m c = 3.86 × 10 − 13 m {\displaystyle \ ={\frac {\hbar }{mc}}=3.86\times 10^{-13}{\text{ m}}} {\displaystyle \ ={\frac {\hbar }{mc}}=3.86\times 10^{-13}{\text{ m}}}). To lowest order in the fine-structure constant, α {\displaystyle \alpha } \alpha , the QED result for the electrostatic potential of a point charge is:[3]"

The math is fine, but the English is murky.

107.3.128.7 (talk) 17:34, 4 February 2017 (UTC)

It reads OK to me. Xxanthippe (talk) 21:28, 4 February 2017 (UTC).

Sentence could be broken up

The below sentence is not very clear and could maybe be broken up into two or more sentences.

The effects of vacuum polarization were first observed experimentally prior to 1947, before shifts in the hydrogen energy levels due to it were theoretically calculated by Hans Bethe[1] on the return train ride from the Shelter Island Conference to Cornell, after developments in radar equipment for World War II resulted in higher accuracy for measuring the energy levels of the hydrogen atom (the Lamb shift) and the anomalous magnetic dipole moment of the electron (corresponding to the deviation from the Dirac equation predicted value of two of the spectroscopic electron g-factor value), measured by I.I. Rabi.

I can't understand what Rabi measured or how that is connected to developments in radar equipment. Also the sentence is three lines long.

Miguelmurca (talk) 11:24, 8 June 2018 (UTC)

I tried to fix it. I hope I got it right. JRSpriggs (talk) 05:50, 9 June 2018 (UTC)

Much better, thanks :) Miguelmurca (talk) 12:07, 10 June 2018 (UTC)

Reference / Citation and Note Needs Verification and Checking

Currently (as of now Note 11) corresponding to reference

Berestetskii, V. B.; Lifshitz, E. M.; Pitaevskii, L. (1980). "Section 114". Quantum Electrodynamics. Course of Theoretical Physics. Vol. 4 (2nd ed.). Butterworth-Heinemann. ISBN 978-0750633710.

is marked as year 1980. However, Course_of_Theoretical_Physics#Volume_4 is marked as 1982 for the same volume and year. The most likely discrepancy being caused by language editions e.g. Russian v. English editions. Can this please be checked and notated accordingly with which language/publisher is being referenced so that no discrepancy exists? — Preceding unsigned comment added by MMmpds (talk • contribs) 20:37, 5 August 2023 (UTC)