Talk:Gluon/Archive 1

How many gluons does quarks emit?
As I understand it all particles with a color charge emit gluons and respond to received gluons? How many gluons does quarks emit?--JR, 12:31, 29 May 2007 (UTC)
 * How many gluons do quarks emit? And, I don't know. -134.50.203.20 (talk) 21:59, 7 October 2008 (UTC)
 * The answer is, it depends what gluon energies you want to consider. As you consider very low energy gluons, the number becomes as big as you want.  Or, to put it simply, infinity. -- SCZenz (talk) 06:33, 8 October 2008 (UTC)

Are gluons really massless?
Question for specialist: are gluons really massless? Following http://hyperphysics.phy-astr.gsu.edu/hbase/particles/expar.html, this is not true. Also, from my (poor) understanding, it is not simply that gluons "bind" the quarks together; they are themselves, sort of, composed of a quarks pair. -- looxix 10:16 Apr 14, 2003 (UTC)
 * Yes they are massless, and nowhere in the linked page states they aren't. You may be confusing them with the W and Z bosons.  Gluons are not composed of a pair of quarks, however they have two color charges, for instance a red-antigreen gluon.
 * The fact that gluons themselves have color charge causes somewhat erratic behavior (as gluons are creating and annihilating other gluons as well), including the limited range. The W and Z bosons also have limited range, but in their case it is caused by their mass.
 * 63.205.40.10 04:01, 23 Jan 2004 (UTC)


 * My copy of the 2002 Review of Particle Physics states that a mass of up to a few MeV may not be precluded, so I added that to the article. -- Schnee 23:59, 26 Jul 2004 (UTC)


 * Could you add the citation to the article please? HEL 17:54, 1 October 2006 (UTC)


 * We have no way of knowing whether gluons are truly massless or not. I'm not even sure it's possible to prove either way. It might not be possible to prove or measure. Also, I should point out that we initially thought neutrinos were massless, until we discovered that they weren't. Stonemason89 (talk) 21:23, 24 August 2010 (UTC)


 * Gluons should be masseless since they are gauge-Bosons, but if they realy are I think is a matter of actuall researchRolteVolte (talk) 19:24, 12 October 2010 (UTC)
 * ok. they do not have rest mass like photon, but they must have some energy? how much energy for one gluon? photon has energy proportional to its frequency. Jackzhp (talk) 04:24, 15 September 2013 (UTC)

What is the point in giving theoretical mass as "0 MeV/c²" (in the frame on the right)? How does it differ from "0 eV/c²" or "0 kg"? If there is a theoretical uncertainty on the level of MeV/c² (which I cannot find in the quoted reference) it should be written explicitly. Otherwise, I find such notation confusing. I would change it to "0" with no unit myself, but I am unsure how the Wikipedia code for the frame on the right frame works. 128.141.24.139 (talk) 17:10, 29 April 2015 (UTC)

8 gluons
I've read several sources that say that due to the subtleties of the theory, there are only 8 gluons, but nobody ever says what they are. Can someone please say what these 8 gluons are, and explain what the subtleties are and why they cause there to be only 8?


 * Maybe this will help (haven't read it in its entirety myself yet): http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/gluons.html -- Schnee 23:15, 26 Jul 2004 (UTC)


 * OK, I looked around a bit more and wrote a short section on this. Can someone who actually knows something about QCD look this over? ;) -- Schnee 23:56, 26 Jul 2004 (UTC)

Okay, as I understand it, there's 6 types of charged gluons (red-antigreen, red-antiblue, green-antired, green-antiblue, blue-antired and blue-antigreen) and 2 types of neutral gluons. That doesn't make sense, why the heck are there two types of neutral gluons? What's the diference between the two types of neutral gluons? -- Gordon Ecker 00:48, 11 January 2005 (UTC)

Ah, the mysteries of the universe. Who can say? Mashford


 * You don't seem to get it. This isn't some great unknowable mystery of the universe. We only know about gluons because their existance is inferred by experimental results. If the only difference between the two types of neutral gluons was something we didn't know about, then we'd think both types were the same thing and assume there were only 7 types of gluons until we figured out the difference, therefore there must be a known difference between the two. -- Gordon Ecker 07:14, 15 January 2005 (UTC)


 * Read the article. The statement "there are 8 types of gluons" is misleading, and shouldn't be taken as being true in the sense that there *really* are only 8 different gluons. There are much more, but they aren't linearly independent, so once you grokked that, it's easier to just say "there are 8 types of gluons", with the unspoken assumption that everyone knows that that's really just a simplification. That being said, colour charge is different from electrical charge etc., anyway - a "red-antired" gluon, for example, wouldn't neutral in the same sense an (electrically) uncharged particle is. Rather, it's "red-neutral" (for lack of a better word); similarly, a "blue-antiblue" gluon would be blue-neutral, and so on. I don't claim to understand all the subtleties of QCD myself (not at all), but I think that it's safe to say that the (natural, from a layman's POV) assumption that colour charge is similar to electrical charge etc. and that there is only one kind of neutrality is wrong. -- Schnee (cheeks clone) 03:19, 17 Jan 2005 (UTC)


 * Yeah, but if, as you put it, 'red-neutral', 'blue-neutral' and 'green-neutral' were different types of neutral then that would produce nine linearly independent gluon types, instead of 8, and if the three were all the same type of neutral then that would mean only 7 linearly independent gluons. I should probably ask around on some physics message board or something. -- Gordon Ecker 22:28, 17 January 2005 (UTC)
 * Okay, quarks can have a charge of r, g or b. Antiquarks can have a charge of -r, -b or -g. Baryons have a net chromatic charge of 0, and are comprised of either 3 quarks with chromatic charges of r, g and b, or three antiquarks with chromatic charges of -r, -g and -b, therefore (r)+(g)+(b)=0, and (-r)+(-g)+(-b)=0. Mesons have a net chromatic charge of 0, and are comprised of one quark with a positive chromatic charge and one antiquark with a corresponding negative chromatic charge, therefore (r)+(-r)=0, (g)+(-g)=0 and (b)+(-b)=0. In other words, colour charges add in a way similar to vectors. Am I getting any of this wrong? -- Gordon Ecker 08:56, 18 January 2005 (UTC)


 * As I understood the article that Schnee linked to, (with my severely limited memory of linear algebra from my senior year of HS, during which I was not paying attention at all) - it's not that $$r\bar{r}$$, $$g\bar{g}$$, and $$b\bar{b}$$ are all mutually equivalent, in which case there would indeed be seven unique gluons, it's that any one of those combinations can be represented in terms of the other two. In other words, the minimal number of unique gluons to describe the theory would be:
 * $$r\bar{g}$$
 * $$r\bar{b}$$
 * $$g\bar{r}$$
 * $$g\bar{b}$$
 * $$b\bar{r}$$
 * $$b\bar{g}$$
 * and any two of
 * $$r\bar{r}$$, $$g\bar{g}$$, or $$b\bar{b}$$
 * the remaining third being describable as a linear combination of the other two.
 * Now, if anybody feeling more prosaic than me wants to incorporate this into the article, Strong interaction and Color charge, I would be much obliged... --April Arcus 16:36, 16 Apr 2005 (UTC)

This whole digression on the number of gluons doesn't make a lot of sense.

For example: "there actually exists an infinite variety of gluons, each of them being a normalised linear superposition" doesn't make any sense. You could say exactly the same thing about any quantum variable.

And the argument cribbed from Baez is actually an explanation as to why sl(3,R) has 8 generators. Though Baez knows that there's a deep connection between sl(3,R) and su(3) that ensures that su(3) is also 8 dimensional, I doubt it's clear to the vast majority of wiki readers.

Honestly, I don't see why it's necessary to explain the number 8 at all. That's just what it happens to be. If QCD happened to be based on some crazy thing like E8, you wouldn't bother to explain why there are 248 gluons, would you? That's just what the number comes out to be.

-- Xerxes 21:33, 2005 Apr 20 (UTC)


 * The reason this needs to be explained is that to the casual reader, there appear to be nine possible combinations between each of the three colors and their anticolors, yet in most introductory level sources, the number 8 is casually stated without any explanation. If the math can be reduced to something comprehensible to a normal human, it should be done. I had hoped my understanding and synopsis of Baez was adequate, but if not, I heartily encourage you to explain it rather than simply strike it. --April Arcus 08:46, 13 Jun 2005 (UTC)

gluon exchange
just got a question, doesnt the gluons emitted compensate for the new color charge? like blue quark changes to red and emitts antired+blue? in the article its the opposite

and someone tell me whats linear algebra?

Linear algebra and why there are 8 gluons
All that one needs to know here is that linear algebra involves manipulations of things like vectors: adding them, forming dot products, rotating them, etc.

Now to counting in the usual three dimensional space that we live in. It is clear that there are three components to a vector. In linear algebra one says that there are three basis vectors. One can choose a coordinate system, and write these basis vectors as the unit vectors in the x, y and z directions. Clearly one has an infinite number of vectors, but they are all linear combinations of the three unit vectors.

Saying there are 8 gluons is like saying that there are only 3 vectors. What one means is that there are 8 basis vectors in the space of gluons, although there are actually an infinite variety of gluons. Why is there a space of gluons? Because (I need jargon at this point) quantum states are elements of a Hilbert space of vectors, and quantum theory is a linear algebra on these vectors. Back to english: quantum fields can be added and subtracted like vectors.

It is also important in linear algebra to understand the notion of rotations. If we make an ordinary rotation in 3 space, then that just mixes up the coordinates of a vector: each coordinate becomes a linear combination of the old values of the coordinates. Another way to say this is to say that the x, y and z unit vectors mix under rotations.

Now why 8 basis gluons. There are 3 colours (this means that there are 3 basis quarks and they mix under SU(3) rotations). Each gluon carries one colour and one anticolour label (red-antigreen, for example). This would give nine. Three of these are red-neutral, blue-neutral and green-neutral. Under SU(3) rotations a red-neutral could become a blue-neutral, for example. But there is a colour-singlet (or colour scalar) combinations red-neutral + blue-neutral + green-neutral, which does not mix with anything else under SU(3) rotations. So it plays no part in the force between quarks which is obtained by exchanging gluons (because an SU(3) rotation would always change the colour of the quark). Hence you throw out this combination, finally getting only 8 quarks.

A last bit of jargon: you can get the dimension of the adjoint representation of any SU(N) algebra by repeating this argument. Bambaiah 05:18, Jun 3, 2005 (UTC)

Resolution to the 8 gluon problem
This is how I understand the situation.

There are in fact two different types of "neutral" QCD particles. There are "colour neutral" particles, which have no net colour charge, where anticolour charges are taken as negative. So red-antired, blue-antiblue, green-antigreen, or any superposition of these, gluons would all be colour-neutral. Also, particles with no colour charge (ie e-) would also be colour neutral. This is the equivalent to QED neutral particles. (ie. hydrogen is neutral because it has 1+ and 1- charge).

However, QCD is more complex in that it also has "colourless" particles. A colourless particle is one that has equal amounts of RGB and equal amounts of antiR antiG antiB. This is the inspiration for the colour terminology since if you add red green and blue light together you get white (colourless) light. So, a proton is definately colourless (only colourless particles are stable) since it has 3 quarks, one of each colour. However, it is not colour neutral. Its colour charge is RGB. This is what leads to the residual QCD force that holds the colourless protons and neutrons together (as opposed to the fundamental QCD force which holds non-colourless quarks together inside the nucleons). The electron is also colourless since it has equal amounts of each colour (namely none!). It is thus colourless and colour-neutral.

A colourless gluon would look like: (note that this is also colour-neutral)
 * $$r\bar{r} + g\bar{g} + b\bar{b}$$

Ok....so now that we have the two types of QCD neutral particles straight the 8 gluon problem is easy. Colour-neutral gluons are allowed, it's the colourless gluons that are forbidden. This is because colourless particles are the only stable particles and if a colourless gluon existed it should have been detected long ago. The colour-neutral gluons, however, are not stable and can't exist outside the nucleous...thus evading our perception except at high energy.

So, there are nine combos of colour-anticolour gluons that are theoretically allowed (including the 3 colour-neutral gluons). However, the requirement of no colourless gluons imposes a further restriction upon the gluon colours. This reduces the number or degrees of freedom by 1. Thus there are only 8. These could be take to be (for example):

and
 * $$r\bar{g}$$
 * $$r\bar{b}$$
 * $$g\bar{r}$$
 * $$g\bar{b}$$
 * $$b\bar{r}$$
 * $$b\bar{g}$$
 * $$r\bar{r} + g\bar{g}$$
 * $$g\bar{g} + b\bar{b}$$

These are all linearly independent and additionally there is no way of forming a colourless gluon through superposition of these gluons. Thus, they form a basis for all experimentally allowed gluons.

If nobody has any objections about this I will update the main page to reflect this.

Danlaycock 20:45, Aug 13, 2005 (UTC)


 * Please don't. This is a solution in search of a problem. There is a simple formula for deriving the number of gluons: N2&minus;1. That's really the end of the story. -- Xerxes 01:56, 2005 August 14 (UTC)


 * I disagree. The fact that there is a simple formula to derive the number of gluons is all the more reason why it should be explained.  If there was a more complicated relation then it would be easier to justify glossing over it.


 * If there had of been 9 gluons it wouldn't have needed any further consideration, but since the number doesn't agree with what one would expect given the number of colour-anticolour combinations it should be explained. Anyone with some basic statistical knowledge can calculate that there should be 9, which leads to much confusion when the number 8 is quoted.  This isn't like trying to explain the number of quarks, which as far as I understand is a purely empirical result.  There is nothing special about 6.  The number of gluons, however, is directly a function of the number of colours in the theory.  And since it is relatively easy to show qualitatively why we think there are only 8 I think that it should be explained.


 * Obviously there are a significant number of people just on this talk page who are interested and/or confused about this topic. I know it's something that bothered me for quite a while.


 * I agree with you in that there is no point trying to explain why it is that there is no colourless gluon...that's just the way nature is. However, how this leads to only 8 gluons should be explained in my opinion.  Obviously the fact that their aren't colourless gluons is incredibly important to the universe that we live in.  If there was one, the strong force could have been a long range force and thus had macroscopic effects.  Thus this fact does have very significant implications.


 * If you disagree with my argument feel free to add or comment on it but I really feel that this issue should be addressed. After all, colour content is essentially the most important characteristic of a gluon and barely any mention of it is made in the article.


 * Danlaycock 04:04, Aug 14, 2005 (UTC)

As someone who came to this page trying to find out why there are only 8 gluons and found Danlaycock's explanation sorted it out for me, I'd say this Xerxes guy needs to think about who this thing is written for... people like me who would like an answer, not a load of "this is a solution in search of a problem" rubbish. So thank you Danlaycock for explaining it.


 * Using the explanation given here, can you now determine the number of force-carrying bosons in an SO(10) gauge theory? If you thought it was 99, you're wrong; the correct answer is 45. How about E6? Is it 35? No, it's 78. That's because the hand-wavy explanation given here is not the right way to solve this problem.


 * For SU(N), the adjoint happens to have dimensionality N2&minus;1. And it happens that there's a deep fundamental connection between SU(N) and the number of linearly-independent traceless real N&times;N matrices. And it happens that you can make up a little story about the N colors and N anti-colors that matches well with those matrices (you take out the totally-symmetric combination to make the matrices traceless). But at the end of that story, you haven't learned anything! Specifically, you still have no idea why it works and when it doesn't. It's bad intuition that will just have to get unlearned later. Or worse, never will.


 * The right way to find the number of gluons is to know that it's the dimensionality of the adjoint representation of the appropriate group, which may or may not bear any simple relation to the dimensionality of the fundamental group (number of "colors"). -- Xerxes 15:39, 2005 August 14 (UTC)

I haven't got a mathematical background, so that "explanation" makes no sense to me whatsoever - I don't even know what an SO(10) gauge theory or E6 *is*. And even if it turns out that I have heard of them I can't understand that notation. So it might not be 'correct' but I'll be sticking to the kiddy-simplified version that isn't flying way over my head, ta very much...

But wait, surely it was you who said further up that the formula was just N2&minus;1, but it's using that on the SO(10) and E6 that comes up with the answers you just said were wrong... So how do you know which is the appropriate group or the fundamental group or whatever? *confused*

And just one more thing... would a red quark turning into a blue quark emit a red-blue, red-antiblue, or antired-blue gluon? I've seen different things in different explanations and I don't know which is right (where does this "anti" thing come from and what does it mean?)


 * I'm jumping in here, but here's my comment: maybe there is no simple explanation. The simplest place I know of to look would be in David Griffiths' particle physics book, which says something about the 9 quark colors being rearranged into an octet and a singlet, and the singlet not existing in nature.  I assume that's a watered-down version of what Xerxes said, which I do not yet have the education to understand either.  To answer your last question, it's red-antiblue.  That way there remains a total of 1 unit of red, and 0 units of blue.  -- SCZenz 17:06, 1 September 2005 (UTC)

Ooh I think I get it, clever! So does that mean that the antiparticle of a red-antiblue gluon is the antired-blue gluon? And this *magic number* of 8 gluons includes those antiparticles? Or am I barking up the wrong tree... I was reading a book by Murray Gell-Mann and he seems to have conveniently ignored the "anti" bits.


 * The gluon is its own antiparticle. But yes, if you include color, then flipping CP (which produces antiparticles, at least as long as you're just dealing with the strong force) will turn a red-antiblue into a blue-antired.  That won't help resolve the counting issue, though, as they're already included in the naive count of 9.  (Red-antired, blue-antiblue, and green-antigreen would all stay the same under a CP flip, which is why you can have an odd number.) -- SCZenz 18:02, 1 September 2005 (UTC)

Eeeexcellent - simplistic though my understanding of this may be, 'tis still enough to supergeek my A level physics coursework... mwahahaha :D Thankies!


 * I think that no matter how "handwavy" this explanation is, as long as it correctly lists the allowed types of gluons and gives a basic explanation, that's really enough for a general-purpose encyclopedia, whether or not it's the "right" way to address the issue. What Xerxes engaged into is intellectual snobbery in its purest form. Just mention that this explanation only works for this specific issue, and it's all that's needed. Most readers of Wikipedia are average Joes, not experts. There are far more people interested in knowing why there are 8 gluons than those who even heard about SO(10) or E6, let alone know what they are. - Sikon (talk) 10:18, 8 March 2008 (UTC)

I would be inclined to agree with Xerxes for the sake of the generality of the argument - the dimensionality of the adjoint representation of SU(N) is indeed N2&minus;1, and the strong relates to N=3 - however I would implore him to keep in touch with the physical too! Sure the result neatly falls out of representation theory, but it is the theory that must be matched to our universe. We should be able to give a good intuitive reason, no matter how 'hand-wavy', as to why what we see does so and I believe Danlaycock has made a good attempt at this. —Preceding unsigned comment added by 129.31.90.101 (talk) 00:36, 2 February 2010 (UTC)

I think the explanation of the 8 color states of gluons to a novice (me!) is sufficient. However, it wasn't clear to me right away what the notation was in the forumlas, and that there are $$N^2$$ combinations. I've introduced the following explanation.


 * This gives nine possible combinations of color and anticolor in gluons. This is list of those combinations with their mathematical representation:


 * * red-antired ($$r\bar{r}$$), red-antigreen ($$r\bar{g}$$), red-antiblue ($$r\bar{b}$$)
 * * green-antired ($$g\bar{r}$$), green-antiblue ($$g\bar{b}$$), green-antigreen ($$g\bar{g}$$)
 * * blue-antired, ($$b\bar{r}$$), blue-antigreen ($$b\bar{g}$$), blue-antiblue ($$b\bar{b}$$)


 * These are not the actual color states of observed gluons.

It's a delicate balance of introducing confusion and introducing an explanation. Maybe other folks have better ideas. --Ashawley (talk) 14:56, 12 April 2017 (UTC)

Numerology of gluons
Again with the silly 3&times;3 and take out the singlet. Unless you're prepared to explain why red-antired, blue-antiblue and green-antigreen form nonsinglet linear combinations, your argument does not follow. And once you've gotten into that level of detail, you might as well use an actually valid explanation of traceless hermitian matrices. The argument as it stood was misleading and wrong.

I still don't see why we should try to convince a novice reader that 3&times;3 is right and then convince him it is wrong (but only by 1). A novice reader does not (and should not) have an intuition for how many force-carrying bosons are associated with a particular gauge theory. It's a complicated topic. These hand-wavy explanations do not do it service. -- Xerxes 18:42, 8 December 2005 (UTC)


 * It should be acknowledged that it appears there should be nine gluons. Once that's out of the way, it must be explained why the appearance is nonetheless wrong, which shouldn't need an especially complex argument.  Whatever form the argument should take, it can't rely upon SU(3) to demonstrate there should be eight, because that's circular reasoning.  &#8227; &#5339;&#5505;  [[Image:Venus symbol (blue).gif|&#9792;]] [ &#5200; ] 19:58, 8 December 2005 (UTC)


 * I would not be opposed to a discussion of why we think QCD is an SU(3) gauge theory and not a U(3) gauge theory. But then a U(3) gauge theory would just decompose into SU(3)&times;U(1), so you'd really just get 8 gluons and 1 sorta-like-a-photon. -- Xerxes 03:18, 9 December 2005 (UTC)


 * Is there any way to get that info (U(3) would decompose into SU(3) and U(1)) into the article? I added the only part I could source, that the singlet gluon would be a "second photon" in some vague sense. I would like to say that more precisely that the ninth gluon *decouples* from the others and that the remaining 8 still look like SU(3), but my IP (phone) edit got reverted for OR instantaneously. Too bad that there's no way to add things that are merely agreed upon by every physicist but not written down anywhere usable. I assume Quora is no good.Patallurgist (talk) 05:02, 2 September 2021 (UTC)

Copyedit of Properties section
The Properties section has some garbled sentences:


 * The gluon is a vector boson like the photon; it has a spin state of 1. Vector particles usually have three spin states, but gauge invariance reduces the number of spin states of a gluon to two; negative intrinsic parity, and zero isospin.  In quantum field theory, unbroken gauge invariance requires that gauge bosons have zero mass (experiment limits the gluon's mass to less than a few MeV).  The gluon is its own antiparticle.

I will try to sort this out a bit. HEL 17:46, 1 October 2006 (UTC)

Big problem for particle physics pages
The discussion pages associated with many particle physics articles are full of questions/discussion/nonsense from people who have no idea about the physics, instead of discussions about improving the pages. I propose we delete all the above rubbish about "why are there only 8 gluons", and anything else like it, so we can focus on actually improving page content. An encyclopaedia entry is not the place for a thorough pedagogical exposition; people can visit discussion groups etc. if they want to learn the stuff properly. Any objections? Shambolic Entity 07:41, 1 November 2006 (UTC)

Flux Tubes
"Flux tubes" are mentioned throughout this article, but not much is said about them. Who discovered (or imagined) them, when were they integrated into the particle theory, Etc. These explanations could be given either in the Gluon page, or on a separate entry. Thanks. Hugo Dufort 19:57, 15 November 2006 (UTC)

Reverted gluon mass change
I just reverted an edit which changed the gluon mass in the info box from zero to 10^-12 attograms. I don't know if this is supposed to be an upper limit or something; the edit was made anonymously and with no comments. HEL 05:29, 29 December 2006 (UTC)

Gluon reference in Jack Chick
I added the Jack Chick reference at the bottom of this article which SCZenz removed. I wasn't intending to add it as a "reliable source" (clearly it is not) but a humorous aside. Would it be appropriate to have a different section for this (e.g. references in pop culture)?

This is the url: http://www.chick.com/reading/tracts/0055/0055_01.asp —The preceding unsigned comment was added by 132.228.195.207 (talk) 21:34, 26 January 2007 (UTC). SCZenz 12:41, 27 January 2007 (UTC)


 * It's total crap, and doesn't belong here or anywhere else
 * Shambolic Entity 01:55, 22 February 2007 (UTC)


 * In principle, you could have a pop culture section; that's better than putting it in External Links, which is intended for information on gluons. I don't know if every single concept Jack Chick expresses an opinion about ought to have a link to his pamphlet, though&mdash;should there be one in Pope, for example?  I think the link is very funny personally, but I am not sure it improves the content of the encyclopedia. --


 * It's not meant to be humorous. He seriously believes that gluons don't exist. It doesn't add anything to Wikipedia anyway, besides an opportunity to make fun of someone's religious beliefs (which I'm fine with, but a lot of other people aren't). -- 67.184.171.30 (talk) 18:20, 8 December 2007 (UTC)

Color neutral gluons
Without color neutral gluons there are six gluons, which is intuitively clear. But this color neutral gluons are counterintuitive. Why wouldn't color neutral gluons have zero color charge, and therefore be able to be free particles? They are color-anti(same)color combinations, but same is true for mesons, so how come are this gluons confined and mesons are not? —The preceding unsigned comment was added by 83.131.14.250 (talk) 22:32, 21 February 2007 (UTC).

Why "Why are there eight gluons and not nine?" and not "Why are there eight gluons and not six?"? --89.172.94.199 22:00, 13 April 2007 (UTC)

A good way, in my opinion, of answering the question of why color-neutral gluons are not colorless is to look at the analogy of magnets. All magnets so far discovered or created are neutral in "magnetic charge"; magnetic monopoles do not seem to exist (just like free quarks). However, you would not describe the magnet as possessing no magnetism whatsoever. Bbi5291 00:55, 12 June 2007 (UTC)


 * But then what's the difference between color-neutral gluons which have color and corresponding anti-color and meson which is also color-neutral and which also have color and corresponding anti-color, that makes gluon impossible to exist alone, while meson is allowed to do so? Magnet analogy won't help here because magnet doesn't have any net magnetic charge (even worse, there are no magnetic charges inside magnet, or anywhere else) so according to this analogy color-neutral gluons also wouldn't have net color charge, so they wouldn't be in color confinement, which is not true for gluons. --83.131.25.35 07:53, 3 July 2007 (UTC)

Linear combinations of basis gluons
No matter what we define as the 8 basis gluons, from them it must be possible to mix them to generate the red-antigreen gluon (which is emitted when a red quark turns into a green quark), the green-antiblue gluon (which is emitted when a green quark turns into a blue quark), and the blue-antired gluon (which is emitted when a blue quark turns into a red quark), as well as the red-antiblue, blue-antigreen, and green-antired gluons. That being said, how is it that they do not mix further into colorless gluons? I find the explanation of "throw away a gluon so that we avoid colourless gluons" misleading; by that logic, you would have to throw away gluons until there aren't enough left for the strong force to work properly (and, at the same time, you would be violating the sacred symmetry between the 3 quark colors). Thus no matter what your basis gluons are, it is "theoretically" theoretically possible for them to mix into a colorless gluon. What is the true explanation? Bbi5291 01:09, 12 June 2007 (UTC)
 * The true explanation is the difference between the SU(3) and U(3), and the fact that we are actually avoiding the color singlet state $$r\bar{r}+b\bar{b}+g\bar{g}$$, based on the empirical observation that particles in color singlets are stable, and we see no stable gluons. You may be thinking that $$r\bar{b}+b\bar{g}+g\bar{r}$$ somehow equates to "colorless", but that is not how the math of SU(3) works.  Each color-anticolor combination is the equivalent of a different number in a 3x3 matrix; so they don't add that way.  See Gell-Mann matrices for the usual basis gluons, which shows the usual basis matrices explicitly; the color singlet state would look like $$\begin{pmatrix} 1 & 0 & 0 \\ 0 & 1 & 0 \\ 0 & 0 & 1 \end{pmatrix}$$, which you cannot produce from the bases of SU(3) (by definition).  -- SCZenz (talk) 16:01, 11 June 2008 (UTC)

Zero color charge?
The properties table in the article says that gluons have "color charge: none". My understanding was that gluons do carry a color charge (hence they interact with themselves, etc.). According to color charge:
 * Quarks and antiquarks have color charge 4/3, whereas gluons have color charge 8.

So which is correct? Is the color charge "none" or "8" ? --129.6.154.43 17:11, 2 November 2007 (UTC)


 * Not sure about 4/3 and 8 color charge as mentioned in color charge article, it is not properly explained there, at least not properly enough for ordinary reader; it was added in 9 June 2005 by Bambaiah (talk, contribs) (this diff may give better insight).
 * Besides that, gluons do have nonzero (not none, but nonzero) color charge and so do quarks and antiquarks, while 8 is the number of the gluons, which is also not properly explained here (it is not explained why not 6 gluons, i.e. why color-anti(same)color combinations are allowed for gluons, while mesons also have exactly such combinations and they are colorless, while gluons aren't). --89.172.4.148 (talk) 17:59, 11 February 2008 (UTC)
 * Actually, Mesons are all in the color singlet state, proportional to $$r\bar{r}+b\bar{b}+g\bar{g}$$. See, for example, David Griffiths, Introduction to Elementary Particles.  Clearly we are not explaining this well right now. -- SCZenz (talk) 02:41, 12 June 2008 (UTC)

You can't assign a number to color charge, since it's not a scalar quantity. Either way, there are (as has been discussed to death), eight different color charge combinations to the gluons. Hpa (talk) 19:18, 7 April 2008 (UTC)

Six gluons?
Are there any sources for the contention that there being six gluons is a common misunderstanding? I've heard nine, but never six. -- SCZenz (talk) 08:59, 11 June 2008 (UTC)
 * how many types of photons? photon has frequency property, so is gluon (wave ...). so if classified by frequency, then infinite? Jackzhp (talk) 01:04, 14 October 2013 (UTC)

New numerology draft
I think we need to start over on the gluon numerology section. If we're going to attempt to explain at all, it's clear that we need to be more precise about what terms like "colorless." So I am attempting a draft here, which will draw heavily on Introduction to Elementary Particles by David Griffiths, which is perhaps the simplest treatment I know that addresses the issue seriously. I'm really not sure if it will end up comprehensible or not, but here we go... /Numerology draft -- SCZenz (talk) 13:03, 12 June 2008

Ok, a first version is ready... tell me what you think! -- SCZenz (talk) 14:40, 12 June 2008 (UTC)

Gluon mass
The PDG says "a mass as large as several MeV may not be precluded". It refers the reader to this paper, which I will look at at work tomorrow. (This is mostly a note to myself, so I don't lose the links.) -- SCZenz (talk) 19:31, 13 June 2008 (UTC)
 * Wrong paper. This is the right one. -- SCZenz (talk) 12:17, 14 July 2008 (UTC)
 * are you talking about the rest mass? as photon has 0 rest mass, but its energy depends on its frequency. gluon should also have frequency, so what is the possible range of its total energy? For photo, we have a complete spectrum. Jackzhp (talk) 01:08, 14 October 2013 (UTC)

"Controversy"
A throw-away panel in a comic, however notable, does not start a controversy. A few blog responses does not constitute ongoing debate. If a substantial controversy really exists, rather than being synthesized from sources like these, then there will be a third-party reliable source that discusses it. -- SCZenz (talk) 18:44, 13 July 2008 (UTC)
 * And using the popularity of the tracts as a whole to support the claim that a specific view asserted in one of the tracts is widely held is an example of the association fallacy. -- Gordon Ecker (talk) 03:04, 14 July 2008 (UTC)

Strong Force
OK, from what I gather, a Gluon is the representation of the Strong Force, right? It hold the nucleus together? It does not say that in the article (that I can find) so maybe I have oversimplified. Jokem (talk) 18:06, 3 November 2009 (UTC)


 * No. The gluon holds the quarks inside a nucleon together. The nucleus is held together by pions. Stonemason89 (talk) 03:55, 25 August 2010 (UTC)

Major overhaul needed
Personally I think this article needs to be put through the wringer, it needs to be written in such a way that laymen can understand it while maintaining the scientific integrity. I feel having a scientific article with as few references as this one is not acceptable so I have started to reference the things stated or removed and replaced things that could not be directly referenced. Anyone who feels like helping please do so, you don't have to be an expert (I only have a Bsc in particle physics) just a reasonable understanding of QCD or the ability to gain a reasonable understanding by doing your own reading. —Preceding unsigned comment added by 86.17.165.140 (talk) 23:11, 18 August 2010 (UTC)


 * Agreed, this article is full of jargon. I've added a little blurb in layman's terms to the lead. Richard☺Decal (talk) 18:47, 13 December 2015 (UTC)

Color singlet gluon = photon?
The article mentions that long-range gluon interactions do not exist and uses that as a reason why color singlet gluons can't exist. But long-range photon interactions do exist. What's stopping us from considering the photon as the ninth gluon? Such an idea might be useful in a Grand unified theory, for example. Photons and gluons have a lot in common (spin one, apparently massless, negative intrinsic parity, no electric charge). So I don't see why we can't group the photon together with the gluons. Stonemason89 (talk) 21:12, 24 August 2010 (UTC)
 * The answer is that we do. Both photons and gluons are classed as messenger particles. We distinguish them by what force they are the messenger for.Donhoraldo (talk) 04:59, 26 February 2011 (UTC)


 * Check Griffiths' book Introduction to Elementary Particles and the chapter on QCD. The color singlet gluon would couple to all baryons with the same strength, and that would show up like an extra contribution to gravity that hasn't been observed. PSimeon (talk) 07:07, 24 June 2011 (UTC)

style
Some paragraphs use american english 'color' others british english 'colour'. I personally don't prefer either, what does Wikipedia? Anyway we should stay consistent and use only one style. If you know what WP prefers, please unify this style. If there is no preference plese use the style which needs the least number of corrections. Thanks --Ernsts (talk) 03:49, 8 August 2012 (UTC)

Second paragraph talks about "color force" but the term is not yet defined.

Deletion
I took out this section, because it's wrong. "Color force" and "strong interaction" are the same thing. ("Color force" redirects to the strong interaction page.)

"Since quarks make up the baryons and the mesons, and the strong interaction takes place between baryons and mesons, one could say that the color force is the source of the strong interaction, or that the strong interaction is like a residual color force that extends beyond the baryons, for example when protons and neutrons are bound together in a nucleus. "

This has confused "strong interaction" and the nuclear force. It should say something like "One could say that the color force is the source of the nuclear force, or that the nuclear force is like a residual color force that extends beyond the baryons, for example when protons and neutrons are bound together in an atomic nucleus." However this is not a good place for it on the page, as the person above said. --Mujokan (talk) 19:22, 21 January 2013 (UTC)

Why was the assertion that "the gluon is its own antiparticle" removed?
I was looking up properties of the elementary particles and wanted to know if gluons include antigluons. I see that an earlier version of this page claimed they were their own antiparticle, like other zero electrically charged elementary bosons (photon and Z boson). It is not clear to me if the gluon is or is not its "own" antiparticle. As far as I can see, this has little to do with the color charge on them. (?). "anti-color" is not that difficult to differentiate from "antiparticle", imho. I suggest that this topic rather than being avoided, as it is at present, be included. I presume color charge would have to be conserved in any annihilation? This has to be part of any student of gluon's studies, so shouldn't be too difficult to answer. (He says)...72.172.1.86 (talk) 18:45, 1 March 2013 (UTC)

Colorless photon
Should "unlike the colorless photon", in the introduction be "unlike the neutral photon"? That seams to make it clearer why electrodynamics is a simpler theory. MathHisSci (talk) 13:56, 6 July 2013 (UTC)

Group theory details / determinant
Under group theory details, it mentions that the matrices SU(3) are unitary (all good there), and have a determinant of 1.

I'm slightly confused by this latter part, as when you go to either the Gell-Mann matrices link or the SU(3) link, the matrices there, while having a trace of 0, do not have a determinant of 1. Unless, of course, I am completely misunderstanding what is meant by determinant, in this case. Which is entirely possible. I suggest that there may be room for some clarification in that section. Or possibly on the related SU(3) article. Mithras angel (talk) 21:14, 20 April 2016 (UTC)


 * Very late answer, but anyways.. you get the gauge transformation matrices by exponentiation: $$e^{-i \Theta \frac{\lambda_n}{2} }$$, where $$\Theta$$ is a real number, and $$\lambda_n$$ is the n'th gell-mann matrix. The group generated is SU(3). The forbidden 9th gluon is then the transform $$e^{i\delta} I$$, the U(1) group. · · · Omnissiahs hierophant (talk) 20:15, 16 December 2021 (UTC)

Assessment comment
Substituted at 16:25, 29 April 2016 (UTC)

Conflation of interpretation and observation
If, during waking sober consciousness I observe you at a certain place and time, I may reasonably infer, short of bizarre circumstance the fact and truth of your having been there at that place and time. If I see your car or other belongings there I may at most 'interpret' these as indicating your presence. Elementary particles below the level of the actually observed hadrons and leptons are merely inferred by the standard model some with greater cogency than others. This is especially true for gluons which are hypothesized to explain other elements of QCD that are are also, thetically, never observed. This article (in a venue directed at the general public) utterly fails to make this distinction clear. 98.4.124.117 (talk) 07:36, 22 June 2018 (UTC)

In layman's terms
(me)"Hadron" is not "laymans terms". Protons and neutrons are pushing it, but at least they constitute all the matter encountered in everyday life (unless you're a particle physicist
 * They form a lot more than protons and neutrons
 * Correct, but nothing you'd expect to find outside a high-energy physics lab, since all other hadrons are way too unstable. All the stuff you interact with on a daily basis is made up of protons and neutrons (and electrons, but they're not hadrons). This suffers from the same defect as "In layman's terms braking is dissipating kinetic energy by means of breaking of covalent bonds and blackbody radiation". My reasoning was that if you want to explain it in "laymans terms", neutron and proton is pushing it, "hadron" is outside the ballpark. Hence the following suggestion:
 * ''" In layman's terms, they "glue" quarks together, forming hadrons such as protons and neutrons."
 * with he intention of keeping it (more or less) in layman's terms, as the sentence promises. Kleuske (talk) 20:50, 10 October 2018 (UTC)