Talk:Quantum field theory

message: This might be an unusual move, but sometimes its good to recognize excellent writing and remind each other why Wikipedia matters. This article has quite possibly the best physics writing I've read on Wikipedia so far. Its incredibly readable for a lay person like myself and has cleared up numerous holes in my knowledge without leaving me feeling like I'm shackled by my lack of formal physics and math education. Good work to all of you and thank you for this page. 2001:44B8:6117:B100:898E:A293:6AE6:817F (talk) 15:17, 2 November 2019 (UTC)
replies: text: A little late to reply to you, but thank you for the kind words! I undertook the task of writing a new article on quantum field theory after the previous version had to be deleted for plagiarism (and general bad writing). I had been an editor for a long time but never written a whole article myself, so it was quite a challenge. I'm happy you enjoyed it or found it useful. Please don't hesitate to improve it further or suggest changes. Yinweichen (talk) 22:30, 20 May 2022 (UTC)
thread_title:  A pat on the back for all of you 

message: Is there a set of ingredients that every QFT has? I sometimes see statements like "consider a QFT with the following property..." or "we will now construct a QFT with..." and I'm wondering what kind of object they have in mind. For instance, does every QFT have an underlying manifold, an action, a Hamiltonian, a Lagrangian, a Hilbert space, observables etc.? If so, what kinds of objects are these things mathematically? Thanks, AxelBoldt (talk) 02:50, 21 November 2011 (UTC)
replies: text: If you can get hold of Stephen Weinbergs "The Quantum Theory of Fields" you would get a pretty precise view of what his view of what any QFT "must look like". Lorenz Invariance and the Cluster Decomposition Principle (distant experiments can't interfere) are Weinbergs main ingredients. There is a Hilbert Space, but Lagrangians (or Canonical Quantization of those) to obtain the QFT aren't set in stone. Even the renormalization requirement isn't set in stone (you'd have to read the book for that). YohanN7 (talk) 10:14, 12 September 2012 (UTC)
thread_title:  What is "a QFT"? 

message: The non-existence of a wave function for a single photon is described here http://en.wikipedia.org/wiki/Photon#Wave.E2.80.93particle_duality_and_uncertainty_principles. Sorry can not find the right way of editing this 'citation needed'  — Preceding unsigned comment added by 112.202.19.32 (talk) 04:32, 5 March 2012 (UTC)
replies: text: thanks - MIRROR (talk) 17:34, 9 March 2012 (UTC)
thread_title:  Citation needed 

message: (repost from WikiProject Physics) hi, i'm not sure if those articles really speak about the same thing. can someone tell me ? the paragraph Axiomatic approaches doensn't even mention the axiomatic QFT article. thanks -  MIRROR (talk) 17:07, 9 March 2012 (UTC)
thread_title:  [[Constructive quantum field theory|Constructive]] and [[Axiomatic quantum field theory|axiomatic]] QFT articles 

message: Layperson here, I'd just like to inform you that this opening sentence is worse than useless:
"Quantum field theory (QFT) provides a theoretical framework for constructing quantum mechanical models of systems classically parametrized (represented) by an infinite number of degrees of freedom, that is, fields and (in a condensed matter context) many-body systems."
It's actually laughable how utterly opaque that is.  Just so you know! :)
--24.5.197.145 (talk) 09:39, 6 July 2012 (UTC)
replies: text: Glancing around I see that others have brought this up and you've responded, "WHAT?!  WHICH!?!"  So here's a good rule of thumb:  If you need five blue links in just one sentence for terms which are essentially meaningless to a layperson, then you're not doing it right.  At LEAST five different terms in that ONE sentence require extensive unpacking in order for it to make any sense.  So yeah.  WAY too much info.  I'd need help with "parameterized," and especially "an infinite number of degrees of freedom."  I also love how right after that particular meaningless word-salad, there's a little "Oh, to put it another way," and then a whole second utterly meaningless word-salad.  Real quality :).  — Preceding unsigned comment added by 24.5.197.145 (talk) 09:48, 6 July 2012 (UTC)

text: scuse me, six blue links; for terms which mean absolutely nothing unless you've majored in this subject.  All of which require multiple page explanations.  So, just to be clear, the lay person would need to go to each of those six pages, read everything there and then come back before they might have the vaguest most remote hope of understanding THE FIRST SENTENCE.  Right, great writing boys.  Just hope all this makes you feel fucking smart.  --24.5.197.145 (talk) 09:11, 10 July 2012 (UTC)
replies: text: Seriously folks, if you can't edit ANY part of this article into readability, why have it at all?  Can't you at least provide a layperson's introduction?  Or is the sole purpose of Wikipedia physics articles to provide undergrads with an intellectual circlejerk that can't be read by anyone outside their major?--24.5.197.145 (talk) 09:52, 6 July 2012 (UTC)
replies: text: Although reading your comments really makes me laugh, what exactly do you expect? Quantum field theory is the most sophisticated physical theory we have, and even people like Witten acknowledge it as uniquely, notoriously technical. If you're that interested, go teach yourself the rudiments of undergraduate physics and come back in a few years. Michael Lee Baker (talk) 20:07, 3 November 2020 (UTC)

text: The preceding bunch of comments by 24.5 make me laugh! I'm a professional mathematician and even have a significant result in mathematical physics. I also am often frustrated when these physics articles are badly written and don't define their terms, not even in blue.  I constantly hammer on about it, either complaining, or fixing, depending on my knowledge of it. Yet at the same time, I strongly recommend following those 5 blue links and reading those 10 or 15 articles. You'll range from the dot product to nuclear spaces. It's the only way. 89.217.26.179 (talk) 07:52, 28 April 2015 (UTC)
thread_title:  Fucking useless 

message: There are some points that the article doesn't make clear.
The main thing is to define what the states are and what the operators are which act on this state (representing observables or otherwise). Would I be right in saying that all states can be build out of the vacuum state "|0>" by applying (sums, multiples, products or integrals of) creation or annihilation operators? To what extent are these expressions formal, i.e. not to be evaluated? (Normal ordering should be mentioned here.) What are the observables and what are the corresponding eigenvectors and eigenvalues? What states correspond to, for example, particles with a definite momentum or position? If the state (the ket vector in Hilbert space) is an element of Fock space, then surely you can't really say that the quantum field should be thought of as permeating space and time with a value at each point (e.g. for spin-1/2 fermions, it's supposed to be a spinor field), as an element of Fock space isn't a function of position? But the Lagrangian density is still defined in terms of position and is used to describe the field's dynamics, so where does that fit in?
If I understand things better, I'll try to clear up the article. Count Truthstein (talk) 22:20, 15 December 2012 (UTC)
replies: text: Any effort towards making this article more accessible and complete would be greatly appreciated. In my opinion, the material that is present is at about the right level (i.e., understandable to someone who has taken regular undergraduate QM), but it is very incomplete. Zueignung (talk) 22:34, 15 December 2012 (UTC)
thread_title:  Thoughts on article 

message: Concerning the "f*@!#~? useless" comments above, would a new article help? C.F. Introduction to angular momentum, Introduction to general relativity, Introduction to quantum mechanics, probably others... I raised this point here also. Thanks, M∧Ŝc2ħεИτlk 15:22, 7 April 2013 (UTC)
thread_title:  New article: [[Introduction to quantum field theory]]? 

message: Many of the criticisms above can be attributed to a difficult to understand lead section. I think the intelligent layman accepts that they may not be able to understand all the mathematical and physics jargon in the whole article, but they quite rightly want an introduction that can give them some intuitive notion of what QFT is about and why it might be important. In that spirit, I rewritten and have tried to simplify the lead. --Mark viking (talk) 21:48, 7 April 2013 (UTC)
replies: text: Looks good to me, there's only so much you can rewrite (I still stand by an "intro" article though - to "absorb" much of the laymen description allowing this article to be as detailed as it needs to be). Anyway thank you! M∧Ŝc2ħεИτlk 21:56, 7 April 2013 (UTC)
replies: text:  Thanks, I'm glad it looks OK. I agree that an intro to QFT article would be a very good thing. The lead for the article is still quite dense in jargon and there are no illustrations to help guide intuition. These and other pedagogical weaknesses could be better addressed in a separate article. --Mark viking (talk) 23:22, 7 April 2013 (UTC)
thread_title:  Rewrote lead 

message: Starting from this edit, to this edit and revert, followed by another revert by an IP. I think the sections should just be removed since they contain details which can just be linked to, but others are welcome to disagree. I fixed the misguided typography because it stuck out too much. M∧Ŝc2ħεИτlk 18:49, 14 May 2013 (UTC)
replies: text: I agree that these new sections are mostly irrelevant to quantum field theory. While physics has had a long development and one can assert a rough hierarchy of dependencies (as shown by your recent illustration), not every physics article needs to cover in detail all previous physics fields that might have bearing on the topic. At most a sentence or two in the history section with wiki links to the various fields seems appropriate. I'll also note that the editor inserting these sections is very new and has also been messing with the physics templates. --Mark viking (talk) 19:27, 14 May 2013 (UTC)
replies: text: Yes. Let's see if there is a third opinion. M∧Ŝc2ħεИτlk 19:58, 14 May 2013 (UTC)
replies: text: I removed them, it's been a couple of weeks. There are complaints below as well. M∧Ŝc2ħεИτlk 07:40, 27 May 2013 (UTC)
thread_title:  New interrupting sections? 

message: From the second sentence in this section, "....came a dilemma: either preserved classical mechanics and abandoned to the rising electromagnetism, and this was preserved and abandoned almost three centuries of predictions solidly confirmed by experimentation " I tried to figure out how to make it read better, but am lost as to what the author was trying to convey.
Kclongstocking (talk) 03:33, 21 May 2013 (UTC)
thread_title:  Under the section "Mechanics, Electromagnetism and Relativity" 

message: Sorry to butt in just like this without trying to amend the article myself but I'm in kind of a hurry (studying for some Physics exams, you know). Just wanted to point out the awful English some sections of the article are written in - almost every second sentence from "Mechanics, Electromagnetism and Relativity" onwards turns out to be barely comprehensible at all! I'd like to take the time to try and rewrite the bad parts myself, but if I am to be the one who does the job you guys will have to wait a while, I'm sorry about it...have a nice day, everyone!  — Preceding unsigned comment added by Marteninthewind (talk • contribs) 15:32, 26 May 2013 (UTC)
thread_title:  Bad English here 

message: This topic is a tricky topic, but just because the ideas are difficult is not a reason for the writing to be bad.  Actually the difficulty of the topic makes it that much MORE important to write well (so the layman can try to learn something).
1.  The intro sentence is too long.  
"In theoretical physics, quantum field theory (QFT) is a theoretical framework for constructing quantum mechanical models of subatomic particles in particle physics and quasiparticles in condensed matter physics, by treating a particle as an excited state of an underlying physical field."
41 words is too much for almost ANY sentence, but even more so when the topic itself is hard.  The problem is the human mind has a hard time remembering of all the different sub-ideas as the sentence "runs on".  Don't feel like you have to construct an entire classification style definition in the first sentence.  And for a topic like this, trying to start with the analytical definition first is probably not most helpful in easing us into the topic.  Instead tell us what subjects it is part of (first) or when it was developed or its importance or the like.  (give us some "so what" and basic orientational ideas first, before wading into the lemma-like definitions.)
2.  There is a lot of repetition:  
"in theoretical physics"..."is a theoretical framework". 
"quantum field theory"..."quantum mechanical" 
3.  The cleanup tag is very offputting to readers coming here.  In addition to a tricky topic, poorly written, we get one of those discouraging, ugly templates staring at us (should be in the Talk page).
4.  If the Intro is too long, consider to have the lead be very small...and then have a section itself within the article that is called overview or intro or something.
5.  Too many equations in the article body.  Find a way to move them to the back into a penalty box or make a spinout for THE TECHIE article, but let the main article be accessible.  Certainly accessible at the front.  
------------------
I know it's hard.  I know there may not be a perfect solution.  But there's not a doubt in my mind that this thing could not be very significantly improved and that the layman could move from getting 0-5% insights to 80% level of understanding.
TCO (talk) 20:57, 4 July 2013 (UTC)
replies: text: Yes - we (at least user:Mark viking and myself) are aware of all this, it just hasn't been done yet. M∧Ŝc2ħεИτlk 09:41, 6 July 2013 (UTC)
replies: text:  I made a start at editing the history section, but even that bit needs more work.  Apart from better wording and exposition, the references do not follow Wikipedia standards.  I'm not in a position to do much more. — DAGwyn 71.121.204.138 (talk) 11:29, 6 February 2016 (UTC)
replies: text: References all templetized and citations now uniformly in Harvard style. All for better reusability. YohanN7 (talk) 12:37, 9 February 2016 (UTC)
thread_title:  this article could be better written 

message: For what it's worth, I feel an article comparing quantum mechanics and quantum field theory is in order.
Suggest Comparison of quantum mechanics and quantum field theory.  — Preceding unsigned comment added by 70.247.167.99 (talk) 13:16, 1 August 2016 (UTC)
replies: text: You should probably bring this up at the physics forum where it would get more attention. YohanN7 (talk) 11:02, 11 August 2016 (UTC)

text: A comparison article is not entirely a bad idea, but it could introduce a lot of duplication and overlap with the main articles like wave function, Schrodinger equation, relativistic wave equations, postulates of quantum mechanics... M∧Ŝc2ħεИτlk 14:21, 11 August 2016 (UTC)
thread_title:  Comparison 

message: Should the parenthetical explanation be i.e. (as in) or e.g. (for example)?Test35965 (talk) 19:20, 10 August 2016 (UTC)
thread_title:  Infinite degrees of freedom can easily lead to divergences of calculated quantities  

message: A long time ago I wrote this article on the Mossbaur effect and used a simple mass-spring system to explain how the gamma rays deliver momentum to the phonon field (in a simple 1
-D model).  Recently I modified that disscussion at Wikiversity:Quantum mechanics/Quantum field theory on a violin string.  I would like to extend that analysis by adding an "atom" that consists of a one-dimensional simple harmonic oscillator that is weakly coupled to the phonon field.  All motion is in the horizontal direction, and the coupling is the simple energy stored in a spring, \tfrac 1 2 \kappa (x-\xi_0)^2, where x and \xi_0 are the displacements of the atom and central mass, respectively.  Has this been done anywhere?--Guy vandegrift (talk) 07:01, 28 August 2016 (UTC)
thread_title:  Question from Wikiversity 

message: User:Hullaballoo Wolfowitz  removed Ken Wilson's portrait indicating it "fails NFCC#8", namely "Contextual significance. Non-free content is used only if its presence would significantly increase readers' understanding of the article topic, and its omission would be detrimental to that understanding."   
This type of peremptory removal has been  perpetrated repeatedly in Renormalization group as well. Omission of KGW's portrait is incontrovertibly detrimental to the readers' understanding: The article fleshes out the history of the triumphant field in the last quarter of the previous century, and, rightly, displays portraits of its creators, with explanations of their exceptional significance. KGW is, of course,  king of the hill, and omitting him (for an odd technical reason ) is downright misleading, conveying the unwarranted perception that he might, somehow, be a secondary "also see". Not so, of course: KGW is all but the "owner", making magisterial sense out of the whole field. His Nobel Prize is one of the most deserving on that "wall of fame". This might not be the place to argue the merits of a wall of fame (in which, e.g., Dyson might well belong), but just a protest at the peremptory exclusion of KGW's portrait on the grounds of a counterproductive technicality.  A novice skimming all this would clearly get the wrong impression. Hell, I've had students puzzling over such twists and omissions of WP all the time. For shame! Cuzkatzimhut (talk) 01:44, 1 March 2017 (UTC)
replies: text: This is a garden variety example of NFCC enforcement. The text this photo is used to illustrate reads simply "They involved the work of Leo Kadanoff (1966) and Michael Fisher (1973), which led to the seminal reformulation of quantum field theory by Ken Wilson in 1975". This statement is quite lucid, and a reader's comprehension of it is not enhanced by the inclusion of a picture of Wilson. The Big Bad Wolfowitz (aka Hullaballoo).  Treated like dirt by many administrators since 2006.   (talk) 14:47, 1 March 2017 (UTC)
replies: text: You are arguing, after all.... you selectively dropped "The renormalization group as developed along Wilson's breakthrough insights relates effective field theories at a given scale to such at contiguous scales". Indeed Wilson shared his NP with these two, but his transcendent primacy is undisputed in this field, QFT. Mentioning important chemists and condensed matter theorists should not detract from the keypoint, notional textbooks in hell or not. At best, his, KGW's,  primacy should be emphasized in the text, but removal of pictures should not serve as a whip to "improve your text, or else I'll make it more misleading for you!". Cuzkatzimhut (talk) 15:59, 1 March 2017 (UTC)
replies: text: And how does a picture improve the reader's comprehension of that secondary reference to Wilson? Whether nonfree content should be used is not at all determined by the importance of the subject depicted. You really should review WP:NFC and the associated WMF policy. The Big Bad Wolfowitz (aka Hullaballoo).  Treated like dirt by many administrators since 2006.   (talk) 17:55, 1 March 2017 (UTC)

text: That's all well and good, but we're talking about striking a balance, and the WMF has directed us not to strike the balance on the terms you prefer. Moreover, the picture of Wilson was the smallest and least prominently placed in the article, and wasn't even included in the article until a few months ago (although the article has existed since 2001). Your argument, it seems to me, isn't consistent with policy, practice, and the apparent local consensus. The Big Bad Wolfowitz (aka Hullaballoo).  Treated like dirt by many administrators since 2006.   (talk) 23:59, 1 March 2017 (UTC)
replies: text: Well, it was only the last in the article, since, as you may have cared to read, he tied the package together, at last!, so to speak. I don't know how to get across to you that he "owns" it. The article got started by newbies and even now it is struggling to improve, no thanks to roadblocks such as this. The photo  was the smallest because it was of poor resolution: I certainly would not object to its being sized up! In any case, I can see you are not in a mood to be convinced, so I'll let others, preferably the Cornel publicity office, or the Nobel Foundation, do due diligence and bypass/fix the problem you created. I'm out of here. Cuzkatzimhut (talk) 01:17, 2 March 2017 (UTC)
thread_title: Gratuitous removal of Ken Wilson's portrait

message: The current revision contains the following sentence.
"In fact most topics in the early development of quantum theory (the so-called old quantum theory, 1900–25) were related to the interaction of radiation and matter and thus should be treated by quantum field theoretical methods. However, quantum mechanics as formulated by Dirac, Heisenberg, and Schrödinger in 1926–27 started from atomic spectra and did not focus much on problems of radiation."
Taken at face value the above seems to contradict itself, since atomic spectra consist of radiation, though not the kind being referred to in the old theory, namely, black body radiation, sometimes called incandescence. I suggest that some distinction be drawn to make the comparison clearer. For example,
"In fact most topics in the early development of quantum theory (the so-called old quantum theory, 1900–25) were related to the interaction of black-body (incandescent) radiation with matter and thus should be treated by quantum field theoretical methods. However, quantum mechanics as formulated by Dirac, Heisenberg, and Schrödinger in 1926–27 started from atomic spectra and did not focus much on problems of non-spectral radiation."
Since I am not a physicist, and do not wish to write anything misleading, I am not making this edit myself.
Dratman (talk) 19:57, 11 April 2017 (UTC)
thread_title:  Black-body radiation vs emission of a discrete spectrum. 

message: I'm currently translating this article to Chinese Wikipedia :zh:量子場論, and have noticed several problems with this article:
# The lack of sources in almost all sections. Who wrote all this stuff in the first place?
# Illogical sectioning -- Why is quantum gravity a "variety of approach", but axiomatic approach is its own section? "Definitions" section doesn't actually contain any real definitions of QFT concepts.
# Disproportionate content -- The technical build-up to canonical quantisation is too lengthy for something that isn't directly in QFT (bosons and fermions in regular QM framework). "Implications" section seems a little too specific for a general discussion of the implications of QFT. The article only alludes to path integrals and Feynman diagrams, arguably the most important concepts in QFT, but doesn't even include a single Feynman diagram.
I plan to write many sections in the Chinese article from scratch, and would like to gauge (heh) the interest over here for a rewrite of many parts of the English article as well. The sections are tentatively divided as:
* History (mostly untouched)
* Principles
** Classical and quantum fields: Using real scalar field as an example, give the Lagrangian and state Klein-Gordon equation. Write the classical field solution as an integral of normal modes.
** Canonical quantisation: Promote normal mode coefficients to creation and annihilation operators and construct the free theory spectrum.
** Path integral: Heuristically explain it as the continuum limit of a series of time steps. Write a path integral as a sum over an exponential of the action.
** Two-point correlation function: State the general formulae for the two-point correlation function in the interacting theory, using both the canonical quantisation and path integral formalisms. Mention Wick's theorem and give the Feynman propagator for the real scalar field.
** Feynman diagram: Give one example of the use of Feynman rules in the phi-4 theory.
** Renormalisation: Copy parts of the current "Renormalisation" section. Mention different types of regularisation schemes.
** Other theories: Briefly discuss theories other than real scalar field with phi-4 interaction, such as QED. Write a couple Lagrangians and maybe mention the changes to Feynman rules.
*** Gauge symmetry: Introduce gauge symmetry and Noether's theorem. Copy parts of the current "Gauge freedom" section. Mention the Faddeev-Popov gauge-fixing procedure and ghosts.
*** Supersymmetry: Copy parts of the current "Supersymmetry" section.
*** (Maybe) Quantum gravity, string theory, topological QFT
* Achievements (new section): State the many achievements of QFT, such as the anomalous magnetic dipole moment, the asymptotic freedom of QCD, and the prediction of the Higgs field.
* Axiomatic approaches: (mostly untouched)
The "Principles" sections are already under way at :zh:User:Yinweichen/Testpage3. Please let me know if this would be a welcome change here on enwiki. I'm also open to suggestions on further improvements (please add condensed matter content!). Cheers. Yinweichen (talk) 08:59, 9 July 2018 (UTC)
replies: text: I've gone ahead and rewritten the English article as well, currently at User:Yinweichen/sandbox. It will be moved over here to completely replace the current article after formatting, given that there is no objection. Yinweichen (talk) 22:49, 20 September 2018 (UTC)
replies: text: From a non-expert point of view I think your new version of the article is a great improvement. In the early days of Wikipedia it was felt that references were not needed in science articles for material available in textbooks or otherwise well-known. Someone would start an article and others would add to it, so organization was not a strong point. It was problems with people putting their own theories into physics articles that started the movement toward providing reliable sources. StarryGrandma (talk) 17:33, 24 September 2018 (UTC)
thread_title:  Should I rewrite? 

message: Almost the entire "History" section, from "Early development" to "The golden age: gauge theory and the standard model", seems to be copied from Stanford Encyclopaedia of Philosophy's entry. See this revision.Yinweichen (talk) 07:41, 11 July 2018 (UTC)
replies: text: Thanks for noticing this. It was copied in Feb 3, 2016. I've removed it and requested the material be deleted from the article history. StarryGrandma (talk) 17:06, 24 September 2018 (UTC)
replies: text: Please check the revision history carefully before concluding that we plagiarized another encyclopedia. I have seen a case where the plagiarism went the other way. Some jokes in the axiom of choice#Quotes article were alleged to have been taken from a certain book. But I found that those quotes were in our article even before the book was published. JRSpriggs (talk) 02:05, 25 September 2018 (UTC)
replies: text: , I agree that copying needs to be checked carefully, especially with all the books on Google books that are compilations of Wikipedia articles from varying dates. However the Stanford Encyclopedia of Philosophy article (written by an expert and peer reviewed) is copyright 2012, and verified at the Internet Archive. The content was copied on Feb 3, 2016 in one edit by a now blocked user. StarryGrandma (talk) 02:40, 25 September 2018 (UTC)
replies: text: To StarryGrandma: Thank you for easing my mind on that. It is a shame that we cannot just block that one section, but have to block the old revisions entirely. JRSpriggs (talk) 02:45, 25 September 2018 (UTC)
replies: text: It really is sad that two and a half  years of history are affected. I wish we had seen this sooner. It seems the topic is so complicated few people watch it in detail. StarryGrandma (talk) 03:57, 25 September 2018 (UTC)
replies: text: Thanks for looking into this. While it is sad that we have to revert so much content, a new article has already been written from scratch to hopefully replace and even improve upon the original content. Yinweichen (talk) 21:40, 25 September 2018 (UTC)
thread_title:  Possible plagiarism 

message: 6-dimensional Calabi-Yau manifolds are intimately related to string theory in 10 dimensions, sometimes extended to M theory in 11 dimensions. I am surprised to find only (1+1) string theory described in the section on Other spacetimes. Could/should these also be mentioned? — Cheers, Steelpillow (Talk) 10:51, 12 February 2020 (UTC)
replies: text: All of the 10-dimensional superstring theories are still 1+1 QFTs. The QFTs of these string theories treat the coordinates of the embedding of a string into its ambient 10-dimensional spacetime as 1+1 dimensional quantum fields. In that sense, the Calabi-Yau manifolds arise in the choice of ambient spacetime on which to define the domain of these "coordinate quantum fields" living on 1+1 dimensional strings. Yinweichen (talk) 22:18, 20 May 2022 (UTC)
thread_title:  Calabi-Yau and M theories 

message: Here are a couple statements that look inaccurate:
Any quantum state of a single harmonic oscillator can be obtained from |0\rang by successively applying the creation operator \hat a^\dagger:
:|n\rang = (\hat a^\dagger)^n|0\rang.
Any quantum state of the field can be obtained from |0\rang by successively applying creation operators \hat a_{\mathbf{p}}^\dagger, e.g.
:(\hat a_{\mathbf{p}_3}^\dagger)^3 \hat a_{\mathbf{p}_2}^\dagger (\hat a_{\mathbf{p}_1}^\dagger)^2 |0\rang.
What about superposition states (such as coherent states)? For a harmonic oscillator, only energy eigenstates can be obtained by successively applying the creation operator to the vacuum.76.176.180.164 (talk) 18:51, 30 June 2020 (UTC)
replies: text: This has been clarified. Thank you. Yinweichen (talk) 22:22, 20 May 2022 (UTC)
thread_title:  Inaccurate statements? 

message: An article on QFT without a definition of what a quantum field is? An article written by another academic who lost sight of reality?  — Preceding unsigned comment added by Koitus~nlwiki (talk • contribs) 21:50, 29 October 2020 (UTC)
replies: text: Defined in section 2.2 through illustration. It is made evident before that it is a quantization of a classical field.Cuzkatzimhut (talk) 03:00, 30 October 2020 (UTC)
replies: text: Perhaps Wikipedia deserves an Introduction to quantum field theory, something similar to Introduction to general relativity that is more less technical and more approachable to laypeople. Yinweichen (talk) 22:24, 20 May 2022 (UTC)
thread_title:  What is a Quantum Field? 

message: Hello,
First of all pardon my english. I would like to point out that somehow electron shown in Feynman diagram within "Other theories" section points backwards in time  whereas the same type of particle points forwards in other diagram, found at the very beginning of this article (to the right, within "Quantum field theory" properties). I've read that correct way to represent a matter particle such as electron in Feynman diagrams requires its arrow to be pointed like in the latter case. I am however not qualified in the field, so... I am just a bit confused with this ambiguous use of arrows. Perhaps it is not considered and error as far as it was explained in the description. Nonetheless if there is an actual discrepancy then it should be corrected, of course if somebody proficient in this field could confirm or disprove my doubts. Thank you. 79.110.203.148 (talk) 11:03, 27 May 2024 (UTC)
thread_title:  Feynman diagram incostistency