# B Gluons creating matter

#### questionator89

Just trying to get to the bottom of a thought.
If glouns interact with eachother or itself, could there be a multiple glouns orbiting eachother?
Could this orbit create acceleration, and mass, and create quarks? Or possibly more gluon mass?

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#### PeterDonis

Mentor
If glouns interact with eachother or itself
They do.

could there be a multiple glouns orbiting eachother?
Gluons are massless, so they can't orbit each other.

Could this orbit create acceleration, and mass, and create quarks? Or possibly more gluon mass?
You can't create mass (energy) out of nothing. But gluons can certainly create quark-antiquark pairs if they are energetic enough:

#### Reggid

...could there be a multiple glouns orbiting eachother?
you should not think of gluons orbiting each other, that is a too naive classical picture that does not apply in the realms of particle physics where the situation is more complicated, but there should indeed exist a bound state of gluons without valence quarks*, called glueball

*that does not strictly mean that there are no quarks involved, becaue there will always be sea quarks in such a bound state, also in a glueball.

#### ohwilleke

Gold Member
If glouns interact with each other or itself, could there be a multiple glouns orbiting each other?
You appear to be describing a hypothetical composite particle most commonly called a "glueball" (although as @Reggid correctly explains, it is really a bit more complicated than multiple gluons orbiting each other). As the linked Wikipedia article's introduction explains:

In particle physics, a glueball (also gluonium, gluon-ball) is a hypothetical composite particle. It consists solely of gluon particles, without valence quarks. Such a state is possible because gluons carry color charge and experience the strong interaction between themselves. Glueballs are extremely difficult to identify in particle accelerators, because they mix with ordinary meson states.

Theoretical calculations show that glueballs should exist at energy ranges accessible with current collider technology. However, due to the aforementioned difficulty (among others), they have so far not been observed and identified with certainty, although phenomenological calculations have suggested that an experimentally identified glueball candidate, denoted
, has properties consistent with those expected of a Standard Model glueball.

The prediction that glueballs exist is one of the most important predictions of the Standard Model of particle physics that has not yet been confirmed experimentally. Glueballs are the only particles predicted by the Standard Model with total angular momentum (J) (sometimes called "intrinsic spin") that could be either 2 or 3 in their ground states.
Mathematically, they have been well described from the earliest days of Quantum Chromodynamics (QCD), which is seemingly easy since their properties are almost entirely derived from only one experimentally determined physical constant, the strong force (i.e. SU(3)) coupling constant. All of their properties are relatively easily discerned from first principles compared to other hadrons.

But, no one has ever observed a free glueball (or, at least, has never been able to prove that what they are observing is a free glueball), although some scalar mesons and axial vector mesons may be a mix of glueball and non-glueball hadron states.

The lack of experimental detection of glueballs, despite the fact that they are expected to have relatively modest masses in their ground states (on the order of 0.5 GeV to 3 GeV, the same mass range as many ordinary hadrons that are observed every day at even fairly low energy particle colliders), and despite the fact that they are completely described theoretically (creating a very specific experimental target to look for), after basically half a century of looking for them, also leaves open that possibility that the actually don't exist for some subtle reason beyond the equations and physical constants of Standard Model QCD.

Gluons are massless, so they can't orbit each other.
The other points are correct, but gravity is not the only force that can cause things to orbit other things (e.g., electrons are bound to atomic nuclei by electromagnetism rather than gravity), and gravity acts of mass-energy not just mass. "Orbit" may be a bit of an oversimplification in both the electromagnetic and strong force cases, but the presence or lack of an orbit doesn't follow from the absence of rest mass.

For example, massless photons orbit black holes when they are in what is called the photon sphere of a black hole.

Indeed, most of the mass of ordinary matter in the universe is derived from the energy of gluons (or gluon fields, depending upon the theoretical context you are describing them with) within in protons and neutrons, not predominantly from the valence quarks, or even from the sea quarks. Energy confined in space is basically indistinguishable from mass for purposes of general relativity.

Could this orbit create acceleration, and mass, and create quarks? Or possibly more gluon mass?
The math involved in applying QCD to real life phenomena is too difficult to do completely on an analytical basis for an exact and complete solution. Instead, what physicists do is approximate strong force interactions using a variety of different tricks. In the low energy (i.e. infrared) context, such as protons and neutrons at rest, a numerical approximation tool called "lattice QCD" is used. In the high energy (i.e. ultraviolet) context, such as particles colliding at high energies in colliders, various techniques that make up "perturbative QCD" are used.

In certain kinds of perturbative QCD approaches such as the Nambu-Jona-Lasinio model, it is useful to think of gluons as dynamically acquiring mass for purposes of doing calculations regarding how strong force dominated systems in the perturbative QCD domain behave, even tough they have zero rest mass. See, e.g., this paper. The extent to which this mathematical tool corresponds to something physically real is debatable, and is, to some extent, more of a philosophical issue than a practical one, which physicists of the "shut up and calculate" school are inclined to think of as not worth answering or ill defined.

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#### PeterDonis

Mentor
gravity is not the only force that can cause things to orbit other things
The issue is not the interaction; it's the fact that massless things travel at the speed of light.

massless photons orbit black holes when they are in what is called the photon sphere of a black hole.
Yes, but the black hole is not made of photons. Photons cannot orbit other photons.

most of the mass of ordinary matter in the universe is derived from the energy of gluons (or gluon fields, depending upon the theoretical context you are describing them with) within in protons and neutrons, not predominantly from the valence quarks, or even from the sea quarks
Sure, but none of this says that gluons can orbit other gluons. If we are talking about gluons inside hadrons, they aren't free and the concept of "orbit" doesn't even apply to them. If we are talking about free gluons (which can't exist in our current universe but could at high enough temperatures, such as in the very early universe), they can't orbit each other for the reasons given above. So either way it's not correct to say that gluons can orbit other gluons.

#### ohwilleke

Gold Member
Yes, but the black hole is not made of photons. Photons cannot orbit other photons.
Another theoretically possible example is a geon.

#### PeterDonis

Mentor
Another theoretically possible example is a geon.
Which is a classical solution in which EM or gravitational waves are confined by their own self-energy, and again, does not correspond to "photons orbiting each other".

#### ohwilleke

Gold Member
Which is a classical solution in which EM or gravitational waves are confined by their own self-energy, and again, does not correspond to "photons orbiting each other".
Particles confined by their own self-energy is a reasonable definition of "orbiting each other".

#### PeterDonis

Mentor
Particles confined by their own self-energy is a reasonable definition of "orbiting each other".
You didn't read my post (or the Wikipedia article you linked to, for that matter). A geon is a classical solution in which waves are confined by their own self-energy. It is not a solution in which particles orbit each other.

#### ohwilleke

Gold Member
You didn't read my post (or the Wikipedia article you linked to, for that matter). A geon is a classical solution in which waves are confined by their own self-energy. It is not a solution in which particles orbit each other.
But, in quantum mechanics, wave-like behavior is seen as simply one way of describing the interactions of particles under particular circumstances. A classical solution involving waves necessarily has a quantum mechanical solution involving particles, someone that the linked article on geons alludes to.

#### PeterDonis

Mentor
A classical solution involving waves necessarily has a quantum mechanical solution involving particles
Only in the sense that "particles" is the word usually used to describe quantum objects. But "particles" in this sense do not have well-defined "orbits", as I already pointed out several posts ago. So in this sense, "particles orbiting each other" is not a good description of whatever quantum model corresponds to a classical geon.

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