Talk:Nuclear force

Question

In File:Pn scatter quarks.png, shouldn't the central pion be color neutral? By working out the gluon colors, it seems that the central pion is made up of two blue quarks, whereas, for the pion to be color neutral, it has to be a blue-antiblue pair.

Note:I have never studied this subject, but just read it as a curiosity, so I might be missing some principles here.

Here is my interpretation of the diagram (top-down). From the proton, a blue up quark releases a blue-antired gluon (i'll represent as br*), and turns red. The br* hits the red down quark of the proton, and becomes blue. (Color A of the pion) Now, this blue quark emits a blue-antigreen gluon (bg*), and becomes green. The bg* is absorbed by a green up quark in the neutron, which becomes blue.

Now, from the neutron (happening simultaneously with the above): The blue down emits a br* gluon,and becomes red. This gluon hits the red down, which becomes blue. (Color B of the pion) The now blue quark emits a bg* gluon and becomes green. The bg* is absorbed by the green up in the neutron, which turns blue.

Everywhere in this exchange, charge is conserved. All particles are color-neutral, except for the pion formed in the exchange. Mesons are always made up of a pair of quarks with opposite colors (red-antired, etc.). But, this pion is made up of two blues. Could someone tell me why?

Also, could someone tell me if any quark changes into another during this reaction? The pion also has to be made up of a quark-antiquark pair, but (without changing a quark into another), it seems to be a down-down quark.

Thanks, ManishEarth^{Talk • Stalk} 10:40, 8 July 2010 (UTC)

The pion is neutral so it has to be made of the two quarks of opposite charge-- either a [down + anti-down] or [up + anti-up]. Actually it's a weird quantum mechanical mix of both of these states, or else we'd have two kinds of neutral pions. You can look at it either way, but there's only one kind of neutral pion. You can see that up/anti-down and down/anti-up pions will be charged +1 and -1 respectively. In THIS diagram the pi-0 is drawn as a down/anti-down (they could as easily have drawn it as an up/antiup), and furthermore drawn as a blue/anti-blue (it could have been either of the other two color/anticolor pairs). That makes it both charge and color neutral. You may ask why the pion quarks made of matter and antimatter don't annihilate, and the answer is that they do! Neutral pions can disintigrate into nothing but photons (2 or 3 or whatever you like), just like an electron/positron pair, or a charmonium "J-psi". In this diagram, which (please note) is a diagram of a repulsion not attraction, a proton scatters off a neutron (or vice versa). The mediator is the virtual neutral pion. This is a little like a neutrino scattering off an electron, mediated by the neutral Z-zero. The same particles go in as go out.

So which particle is matter and which antimatter in the pion? In these diagrams the particles are "matter" if they are moving in time in the direction of their arrows. So in this pion, if the pion is going upward, the line represented by the blue upward arrow is the "particle" (the blue down quark) and the one forced to go the opposite way to the pion flight and thus opposite to its arrow, is the "antiparticle" (the antiblue antidown quark). BUT since you can picture the pion going in either direction (from proton to neutron or from neutron to proton) your choice of which of these is the quark and which the antiquark (the left one or the right one) is dependent on which direction you pick for the pion to move as a whole. It works out the same either way, which I suppose is why it's not shown one way or the other in the diagram. In the diagram you can see that an up quark gets changed to a down, and a down to an up, in each nucleon. The net result is no change in each particle. For charged pion interactions, a down is changed to an up in one particle and vice versa in the other, and neutron changes to proton and vice versa, in the interaction. Each of the 3 pions (+, -, or uncharged) come in blue-antiblue, red-antired, or green-antigreen varieties. We see only one of them here. SBHarris 02:01, 9 July 2010 (UTC)

I think I understand... So then (Out of the different possibilities) can this be viewed like this?

• The blue and red quarks in the proton undergo the same reaction which I wrote above and create the blue quark in the meson.
• The green quark in the proton releases an antiblue-green gluon and becomes blue.
• This gluon becomes a pair of (virtual?) quarks, one green (goes to the proton), and one antiblue (becomes part of the pion)

No, when the green up quark releases an antiblue-green gluon, it becomes a blue up-quark (same proton, now on the right). That antiblue-green converts the blue down-quark from the pion into a green down-quark, which then becomes part of the outgoing proton. Remember the gluons are the little chain-like things (always two colors-- one color the other an anticolor), the colored straight lines are quarks and they stay quarks (even the same kind of quark) in strong interactions.

Then where can the anti down come from? As you said, quarks cannot change into other quarks. To form an antidown, thus, Some sort of decay/reaction must occur. The only one I can think of is the conversion of a gluon into a down-anti down pair. So, if the pion is going from the proton to the neutron, the red down will become blue and go off with the pion, while the green up will emit a green-anti blue gluon which will form a green down and a blue antidown, which goes off with the pion. If the pion goes from neutron to proton, the red down becomes blue and enters the pion, while the green up emits a gluon which forms a down and an anti down. The anti down goes off with the pion. Is this correct? ManishEarth^{Talk • Stalk} 12:21, 13 July 2010 (UTC)

Yes. Which ever way the pion goes, the blue down going THAT way has, in some ways, a simpler history-- it's a red down that interacts with two gluons to change to first blue (in the pion) and then to a green down at the end. It stays a down the whole time and changes color twice. BUT for the OTHER blue-down that you pick as the one that is doing the opposite way the pion is going (and is thus an anti-blue antidown) the history is more complicated. Each one of these has to be made as a new anti-down from a new [green down PLUS antiblue-antidown] pair. This comes from a green antiblue gluon that originates from a green particle that changes to blue, and thus emits a green-antiblue gluon that undergoes pair production to become an antiblue antidown (in the pion) and a new green down that stays with the original particle. The antiblue antidown in the pion anihilates a red down in the other particle, and the resulting red-antiblue gluon is available to turn some blue quark in the other particle (either an up or a down) into a red version of itself. SBHarris 06:40, 18 July 2010 (UTC)

So it happens like I said? Production of a short-lived pair from a gluon of which the antiparticle annihilates? It's much clearer now... Thanks a million! ManishEarth^{Talk • Stalk} 09:08, 18 July 2010 (UTC)

P.S. I'll try to make the animation soon. ManishEarth^{Talk • Stalk} 09:14, 18 July 2010 (UTC)

• The virtual antiblue annihilates with the red (in the neutron) and releases an antiblue-red gluon. This annihilation makes the virtual green quark in the proton real. (One question: Can quarks of different colors annihilate/form virtual pairs if the appropriate gluons are present?)
• The gluon turns the blue quark in the neutron red.

No, the green quark line crosses the antiblue-red gluon line, but there's no interaction there-- it just happens to go over the top of it in 2-D. But there's no connection. Ignore the crossing. This is best seen as a blue up-quark emitting a blue-antired gluon to become a red up-quark. The blue-antired gluon combines with the red down-quark to turn it into a blue down, which goes off with the pion. It's a blue down or blue anti-down depending on which direction the pion is coming in. The same is true of the OTHER down quark in the pion-- one of them is down, the other antidown, depending on which direction the pion goes. In gluon interactions the quarks can only change color-- they can't change type (up cannot change to down, etc). If you see an interaction where an up and a down go in, an up and a down have to go OUT (although they will have switched colors). So if it looks like up turns to down, that's actually not true. All that happens is colors have switched. It takes weak force interactions to change an up to a down quark and vice-versa (like beta decay).SBHarris 00:46, 10 July 2010 (UTC)

Thanks, ManishEarth^{Talk • Stalk} 04:41, 9 July 2010 (UTC)

Could you also answer this question? When a body experiences increase in mass because of its speed, is the increase in mass due to particles being created by the energy, or is it just increase in apparent mass? In other words, if you accelerated a particle to near lightspeed, would smaller particles appear to accompany it, or would it just seem to be more massive. I tend to believe the second possibility, because the new particles (from the first one) would have to exist when seen from certain reference frames only. Thanks, ManishEarth^{Talk • Stalk} 05:02, 9 July 2010 (UTC)

The question of mass increase is complicated and you should read mass in special relativity to get a feel for it. Basically, there are two types of mass, one of which goes up with speed and the other of which does not. Generally in the Dirac view, the increase in relativistic mass is actually associated with the appearance of virtual particle-antiparticle pairs, which can become real particles if enough mass-energy (kinetic energy) is supplied, and there is something to transfer the momentum to when the new real pair is created. Otherwise, the virtual pair sort of go along for the ride, supplying the extra mass (or momentum, if you like) but not extra charge (since that does not change with velocity-- so the virtual particle antiparticle pair insure that mass can go up without charge increasing). SBHarris 00:46, 10 July 2010 (UTC)

Hmmm... If the kinetic energy is supplied, will both the occupant of a spaceship and an observer see the new particles? Because the virtual particles only exist for the observer, while the occupant detects nothing wrong. As long as they are virtual, they are unobservable anyways, but then, if they are made real, will everyone see them? I find it hard to digest that a particle can exist selectively for different observers... ManishEarth^{Talk • Stalk} 12:21, 13 July 2010 (UTC)

No, for a single particle, only the observer that sees kinetic energy for that particle (which is frame dependent) sees the new virtual particles that travel with it (and only that observer see the extra momentum, energy, and so on). Since they never become real, there's no problem with one observer seeing them and another not. To make them real, you need a second particle to provide a reference, and then all observers see the new particles as capable of being made by the invariant mass that represents the kinetic energy (the invariant mass is the same for all observers). All observers see the same kinetic energy available to make new particles, but each observer locates it in a different place. For example, in a two-electron collision with a center-of-mass energy to make an electron/positron pair (1.022 MeV), the observer on one electron sees the other electron with 1.022 MeV kinetic energy, but an observer on the other electron sees it all on the first electron. An observer in the COM frame sees it divided between the electrons. SBHarris 03:23, 30 July 2010 (UTC)

Aah, I see. Thanks a million... Could you also answer the wuark question above (It's hard to see, so I added a star)? I'm thinking of creating an animation of one of the possible ways it can happen. Thx, ManishEarth^{Talk • Stalk} 03:38, 18 July 2010 (UTC)

Hope you don't mind another perspective. Gravity is an electromagnetic phenomenon produced by quarks and their quantum chromodynamic motion. The phenomena is net neutral and has no effect on slow moving particles. Relativistic speeds are needed to move with the gravitational EM intensity peaks and produce a measurable effect. If a particle was able to move at the speed of light the push forward would be zero you cant exceed C but the push back would be continuous and powerful hence the particle is suddenly massive due to moving at C. Bill field pulse (talk) 20:22, 1 April 2024 (UTC)

Strong nuclear force

The term strong nuclear force has been historically the common name for this topic, but does not currently even get a mention in the article lead, despite the term redirecting to this article.

This is just plain ridiculous IMO. Interested in other views. Andrewa (talk) 07:02, 26 December 2020 (UTC)

I've added it, lets see if it remains. I think the main issue is its potential confusion with Strong interaction. But I agree it is its historical name (citation needed, however!). Bdushaw (talk) 03:48, 27 December 2020 (UTC)

fm

In nuclear physics, the fm unit is the Fermi. Conveniently fm sounds like Fermi, and also comes out femtometer. (Or femtometre, depending on where you are.) I suspect also in high energy physics. Gah4 (talk) 07:01, 22 December 2023 (UTC)

Quark Motion and quark distances

Quarks are likely to be separated by far smaller distances than a neutron diameter. Because they move 0.8 C and higher the Electromagnetic field intensity will have an intensity pulse in the direction of motion each time a quark cycles past. Let the quarks cycle in a roughly fixed pattern of two like quarks separated by the opposite sign quark with one like quark leading and one trailing. The magnetic field intensity wakes they will produce will cause magnetic curving forces that are balanced with one of the other quarks causing a curving force and the remaining causing a straightening force, true for each of the three quarks. Speed of light causes an additional barrier stabilizing the structure. Does this type of thinking open the door to electromagnetic forces being involved in quark attraction?

Also note that while a trio of quarks in a second proton sits inside the intensity wake of a first proton. The repulsion from highest intensity is towards the other proton. This would explain why at particular short distance the electromagnetic force is strong and attractive. Does this kind of thinking suggest a way that relativistic electromagnetic field forces could hold two protons together?

On a distantly related note when two wires attract an alternate theory is that the electrons seek the less dense fields behind other electrons. (To me this is far more likely than the favored theory of more dense packed protons due to relativistic shortening.) Bill field pulse (talk) 20:27, 20 January 2024 (UTC)