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76 votes
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Why have our eyes not evolved to see "gluons"?

In short, the answer is: because gluons behave in a way that makes them useless for this purpose. To understand why, let's back up a little and look at how photons are useful, and then see how gluons ...
Mike's user avatar
  • 15.3k
35 votes
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How (or when) do gluons change the color of a quark?

The idea that baryons contain three quarks is a significant oversimplification wrong. It works for some purposes, but in this case it causes way more confusion than it's worth. So you should stop ...
David Z's user avatar
  • 76.6k
33 votes
Accepted

Why so much kinetic energy inside a proton?

The simplistic answer is that a proton is very small. The quarks are not free, but are confined to a small region. By the uncertainty principle a small uncertainty in the position of the quarks ...
Dale's user avatar
  • 102k
21 votes
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Why are gluons believed to be massless?

Simply put, the Higgs isn't charged under the strong force. It doesn't have standard electrical charge either. The $W^{\pm},Z$ bosons aquire a mass through the Higgs mechanism because the Higgs ...
Mr.Weathers's user avatar
19 votes

Why so much kinetic energy inside a proton?

I'm sure the word 'quantum' will begin to show up around here, but the question that bugs me is, would it be possible, theoretically, to take the components of a proton, and very carefully place them ...
naturallyInconsistent's user avatar
18 votes

Why are gluons massless as their range is finite?

The important difference is: gluons are charged (carrying color charge and anti-color charge, e g. $r\bar b$) while photons are not charged (zero electric charge). The resulting gluon-gluon ...
Thomas Fritsch's user avatar
15 votes

How (or when) do gluons change the color of a quark?

The model you are thinking about is really rudimentary and cannot explain the dynamics of Quantum ChromoDynamics, QCD . In this link there is a better exposition of what a proton is, within QCD. ...
anna v's user avatar
  • 234k
15 votes

Why are gluons believed to be massless?

One has to keep clear in mind that the standard model, which has the SU(3)xSU(2)xU(1) structure is called standard because it describes extremely well an enormous number of particle data and is ...
anna v's user avatar
  • 234k
14 votes

If massless objects ALWAYS travel at the speed of light and gluons are massless, how are they trapped within hadrons without a need for event horizon?

That quarks and gluons are trapped inside hadrons is called color confinement. As far as I know: it is unrelated to black holes but I don't read Phys Rev D... it's possible it has been suggested ...
JEB's user avatar
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13 votes
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Does a gluon have mass or not?

The Standard Model was explicitly constructed to match experiments. As of today, we have no reason to believe gluons should be massive - and as you can see, the experimental upper bound is very tiny -...
AccidentalFourierTransform's user avatar
12 votes
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Do gluons mediate the interactions between different flavors of quark?

The answer is very simple. For example, let's consider QED with an electron and muon field, $$\mathcal{L} = \bar{\mu} (i \gamma^\mu D_\mu - m_\mu) \mu + \bar{e} (i\gamma^\mu D_\mu - m_e) e - \frac14 ...
knzhou's user avatar
  • 103k
12 votes

If massless objects ALWAYS travel at the speed of light and gluons are massless, how are they trapped within hadrons without a need for event horizon?

Now, to make the light trapped within a small region of spacetime, we need curvature so big that it causes an event horizon, so now we have a Black Hole Photons do not carry an electric charge. So ...
Maury Markowitz's user avatar
10 votes
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Is it possible for an isolated quark to exist if it's bound to one or more non-virtual gluons to render the system color neutral?

It boils down to whether one can make a color neutral particle with a quark and some colored gluons. The rationale for the concept of color can be highlighted with the case of the omega-minus, a ...
anna v's user avatar
  • 234k
10 votes
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Is the gluon also a repulsive force?

Description of force inside the nucleons (between quarks): The strong force is pretty weird, we can't even compute exact solutions for it in quantum field theory (that is the most accurate description ...
Guillermo Abad Lopéz's user avatar
10 votes

Why are gluons color charged but not photon? Could there be a charged EM force carriers like gluons or neutral color charge carrier like photon?

Being charged under a symmetry group means transforming in a non-trivial representation of the group. The carrier boson of a force associated with a gauge symmetry transforms in the adjoint ...
ACuriousMind's user avatar
  • 126k
9 votes
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What's the difference between a meson and a glueball?

This is a good question, and the basic answer is "there is no rigorous difference" (which is the main problem with experimental efforts to identify glueballs). 1) Electrically charged states, or ...
Thomas's user avatar
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9 votes
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How do we know that gluons travel at the speed of light?

Gluons, like quarks, are bound inside nucleons. However, it's not quite correct to think of either quarks or (especially) gluons as being little particles inside a nucleon. Before addressing questions ...
Chiral Anomaly's user avatar
9 votes

Is it possible for an isolated quark to exist if it's bound to one or more non-virtual gluons to render the system color neutral?

You can prove that this is impossible using Young tableaux. The trivial (color-neutral) representation 1 must have 3 boxes in each vertical column. (You can prove this to yourself using the hook-...
Xerxes's user avatar
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8 votes
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Why Do Glueballs Have Mass, When Individual Gluons Are Massless?

If you had a gas of photons in a perfect cavity and these photons had energy $E~=~h\nu$, then for $N$ photons the cavity would have a mass $m~=~Nh\nu/c^2$ of photons. Glueballs as similar. The gluon ...
Lawrence B. Crowell's user avatar
8 votes
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What is the ratio of gluons to baryons?

I asked a question very much like this several years ago (in person, not online, but someone else asked it here): "what's the baryon asymmetry of the proton?" Thinking, of course, about the three ...
rob's user avatar
  • 91.1k
8 votes

Gluon photon mixing -- why not?

In the standard model the Higgs field only carries hypercharge and isospin, but no color. As a result the gluon does not mix with the photon or $Z$. Remember that the original gauge fields, $U(1)$ ...
Thomas's user avatar
  • 18.7k
8 votes
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Number of gluons inside a proton/neutron

The question of the number of gluon a proton consists of is not well posed. Let's start with a simple example, the H-atom. A constituent model of the H-atom would say, the H-atom consists of 1 proton ...
Frederic Thomas's user avatar
8 votes
Accepted

Do gluons care about flavor?

Flavor is entirely orthogonal to color - the gluon(s) neither "know" nor "care" about flavor, but the existence of different quarks still leads to phenomena descending from the ...
ACuriousMind's user avatar
  • 126k
8 votes

Is the concept of bicolored gluons mathematically precise/meaningful? Please explain

Quarks have color charge, but antiquarks have anticolor charges. Baryons form color singlets by including three quarks with all three colors. But mesons form color singlets by having a quark and an ...
rob's user avatar
  • 91.1k
7 votes
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How big of a neutron star would be needed to form a quark star inside of it?

A quark star may or may not be possible - as the wikipedia page you refer to says - they are "hypothetical". As the mass of a neutron star increases, generally speaking, it become smaller and the ...
ProfRob's user avatar
  • 132k
7 votes

How can massless gluons interact with each other?

That's...not how special relativity works. Your question seems predicated on the idea that massless particles "experience no time", because special relativity says that "time stops at the speed of ...
ACuriousMind's user avatar
  • 126k
7 votes
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Do gluons interact with each other by the strong foce?

If you take a look at the QCD Lagrangian describing the strong force \begin{align} \mathcal{L}_{QCD}= \overline{q}(i D_\mu \gamma^\mu - m) q - \frac{1}{4} G_{\mu \nu}^a G_a^{\mu \nu}\, , \end{align} ...
DomDoe's user avatar
  • 523
7 votes
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How do we know that gluons have no electric charge?

It is a brute experimental fact, already apparent within the first year or two of the discovery of the structure of nucleons, in the late 60s, at SLAC. Deeply-inelastically scattering electrons off ...
Cosmas Zachos's user avatar
7 votes

Is the gluon also a repulsive force?

Lets start from experimental facts. The proton exists and is stable. This means that at the quantum level there must be one stable wave function a solution of the complicated potentials of both the ...
anna v's user avatar
  • 234k

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