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Comment by AnimalMuppet | Hacker News Reader

TL;DR: Most of the mass comes from the energy of the strong force interactions of the gluons, not from the quarks. The gluons are not charged; the quarks are. The quarks sometimes go beyond the region of most of the gluons, which gives the proton a larger charge radius than mass radius.

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In fact gluons have a QCD charge, they just don't have a QED (electric) charge. That QCD charge is basically one color and one anticolor, minus the trace. So there are 8 different basis vectors that define the space for what the charge of a gluon is.

Note that "charge", when used without a qualifier, typically refers to the electric charge (which is the origin of the term). Color charge and weak charge are named "charge" only by analogy - there is no physical mechanism underlying all quantities named "charge" (though there is a mathematical definition of why a physical property can be considered a charge or not).

Even mass itself can be viewed as a "charge" corresponding to the gravitational field.

> The quarks sometimes go beyond the region of most of the gluons, which gives the proton a larger charge radius than mass radius.

This is one hypothesis, but not a stated fact in the article.

Fair. On the other hand, the charge can't be coming from the gluons, nor from the strong force itself, so it kind of has to be coming from the quarks. (Um, unless it's inducing virtual pair production out there, and the destruction mechanism involves the pair getting destroyed by interaction with the quarks, and it takes one of the pair longer than the other... something like that could lead to charge out there farther than the quarks actually go.)

Why are gluons needed to hold quarks together. If the 3 are in a line, equally spaced, with the oddball charge in the middle, they will attract quite strongly.

+2. -1. +2

If these charges are equally spaced, the attraction of the middle one in stronger than the repulsion of the outer two.

It's not necessarily a questions of "need". Physicists are just measuring what protons ARE. Whether or not gluons and the strong force are necessary to form an object that looks like a proton is a separate point from what protons actually look like in our universe.

To your point on if such an arrangement would be possible or not ignoring the strong force, it would not. The "net-charge" viewed from the +2 quark would be repulsive, resulting in an unstable arrangement of matter, even if you could construct it in an equilibrium state it would be the unstable kind.

Good point! But it's also an unstable system: the -1 will get attracted to one of the +2 charges and (from a distance) look like a +1, and the other charge will fly off to infinity.

I guess we could design a bunch of picometer-scale scaffolds that hold everything in place and this might work, but that doesn't seem to be the way nature put things.

Sure, but what if they're orbiting the center charge at relativistic speeds? Now they also create a magnetic field. My guess is that somehow it ends up being dynamically stable. Also that the strong force holding the nucleus together is actually mostly magnetism.

I would also posit that just maybe there is such thing as an electrostatic black hole. When matter is accelerated gravitationally to speed c, you reach an event horizon. Same should happen if the acceleration is due to charges, but will happen at a scale similar to the size of baryons. I'd say there is a lot of room for some theoretical developments in this area.

> Also that the strong force holding the nucleus together is actually mostly magnetism.

If that were the case, you would expect protons to tear apart in the presence of strong electric fields. The fact that this seems impossible suggests pretty strongly

Stuff will only keep an orbit if it has nothing else to do, i.e. if it is dynamically stable.

The strong force is much stronger than the Coulomb (charge) force.

nit: gluons aren't electrically charged. They carry strong charge.

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