Why Gravity is Significant in Proton & Neutron Nuclei

[quantumdude]

I am not saying that gravity accounts for nuclear stability.

If there is no strong force to provide the stability, then something else must do the job. It's as simple as that.

Obviously the force of gravity is not sufficient to account for the binding energy of a proton and neutron (ie. the energy required to unbind them). I am suggesting that the explanation for this energy barrier might not require the existence of a mysterious nuclear force at all. If that is the case, then gravity might be the only force in the nucleus.

There's nothing mysterious about the strong interaction. It's only mysterious to people who have not studied it.

An analogy would be to very dense and heavy ball bearings (pretend they are made from neutron star matter) sitting on a level frictionless surface at the bottom of a deep Earth well. Their own gravity would attract them to each other and keep them together but is not the force that keeps them in the well. I am suggesting that there may be some energy barrier that keeps the nucleons from leaving the region of the nucleus, but that it is not a force x distance energy barrier (that is where the analogy ends, of course, because the energy barrier that keeps the ball bearings in the well is Earth gravity x height of the well).

This is just silly. The energy well has to correspond to some potential. Don't you see that you're replacing the (well-understood) strong+weak+EM interaction with gravity and a mysterious energy well? Where does this well come from? God?

It isn't necessitated. The question is whether observational evidence can have an alternate explanation. In case you haven't noticed, I don't like the strong nuclear force.

You don't understand the nuclear force. This can be remedied with some study.

But if the ball drops, it is not moving toward the skater (the grabber). That means the skater has stopped the ball. Since the momentum of the ball in the direction of the skater has to equal to the momentum of the skater in the direction of the ball in the original frame of reference (ie. before the grab), the skater stops moving.

No. The if the ball is dropped after the exchange, then the skaters continue moving towards each other. There has to be another exchange to stop the skaters.

The forward momentum of the skater has to equal the backward momentum of the ball. When the ball stops, the skater stops.

Will you please work out the calculation? It's quite simple. You have a skater carrying a ball, and they are both moving at speed v. If the skater drops the ball, the skater does not stop. In fact, the skater moves faster, because of the reduced mass.

Do you not agree that in the original rest frame, the position of the center of mass of the skater and the ball cannot change?

Yes.

So either the ball keeps moving past the skater's back (ie he throws it behind him) and the skater keeps moving forward toward the other skater, or the ball and the skater stop.

No.

Please do a calucation, and you'll see that it does not work like this.

That is what I originally said because, as I explained, I didn't think you were relying on transfer of momentum because unless the ball was very heavy the skater would not move very far toward the other skater.

Please look up the definition of momentum. The ball need not be very heavy, if it is moving fast. I already explained this.

In my subsequent post I said that the skater would move toward the other skater a little bit and then stop. I said: "I can see how repeated back and forth motion of the same ball via alternating grabs by each skater would move them gradually closer together." And I went on to take issue with your suggestion (perhaps I misunderstood) that once the skater began moving as he pulled the ball towards himself, he would continue moving toward the other. I said that he would only continue until the ball reached him and stopped. I still stand by that. I said "But that momentum lasts only until the ball stops with the grabber"

And that is wrong.

I guess I don't know what you mean by 'attraction'. You cannot mean 'motion' because once the ball has stopped, the skater has to stop. (Or are you suggesting that the skaters are skating as well? {that was a joke})

Whatever happens on that frictionless ice surface, the center of mass of the 2 skater and ball system cannot move. I think we have to agree on that.

By "attraction" I mean that the skaters continue to move towards each other. While it is true that the center of mass of the entire system must not change its momentum, it is not true that the individual constituents of that system must stop moving. And no, the skaters need not have been skating prior to the exchange.

If the skater who pulls the ball towards him never stops the ball (because the other skater grabs it back before it reaches his chest) and this is kept repeating, the two skaters will continue to move together. But I didn't think that was what you were saying because I thought you said the motion of the first skater to grab the ball would continue even if the ball was dropped (ie. after the first grab).

That is precisely what I was saying.

I am not struggling with momentum at all. I am struggling with your example. I assure you I have no problem with basic physics. I studied physics from 1972-1976. That was a long time ago. I have't heard that the principle of conservation of momentum had changed since then.

You are indeed struggling with the idea of momentum.

First, you believe that only a very massive ball can impart an appreciable momentum transfer. But that is wrong because p=mv, so a lightweight but fast moving ball can also impart such an impulse.

Second, you believe that a system with total momentum of zero implies that the momentum of all the constituents must also be zero. But that is also wrong. Once a momentum transfer takes place (as in, say, the exchange of a ball from one skater to another), the center of mass of the system is motionless despite the fact that each skater continues moving. If a momentum q is imparted to skater 1, and a momentum -q is imparted to skater 2, then the total momentum is conserved and the skaters continue on their merry way, towards each other.

I don't know how to make it any clearer than that.

I don't need to revisit classical mechanics. I am rereading my 4th year quantum mechanics text and my 2nd year EM text. I appreciate that you are trying to be helpful, but I think that we are just misunderstanding each other's posts here.

No, you're understanding my posts just fine. It's just that you need to brush up on basic physics. I'm sorry that you disagree, but it's true.

 

[anti_crank]

I am not suggesting that EM theory breaks down for EM waves with wavelengths smaller than $10^{-15} m.$. I was just questioning whether we really have evidence that the coulomb force between protons continues as their 'separation' distance becomes smaller than $10^{-15} m.$. That may have more to do with the structure of the proton than EM theory. EM theory assumes point charges and does not explain what creates the coulomb force.

My point was that if you change Coulomb's law to act differently on those scales, you have to change Maxwell's equations as well, and so you change the properties of EM waves on those ranges. This consequence cannot be avoided.

If you're suggesting perhaps that protons have a charge distribution that may end up reducing the repulsive force, you may be partially correct. However, since the net charge on both protons remains positive, the net force will necessarily be repulsive, will equal the point-charge repulsion formula to a first order approximation.

Hang on. I am not talking about new gravitational effects. I am not suggesting that some new gravity would account for the huge binding energy of nucleons. I am just questioning whether we have to use traditional concepts of force x distance to account for that binding energy.

The traditional concepts of force x distance are not the right tools for this job. You need quantum mechanics for any analysis of nuclear structure. Let me add here that all alpha decays can be modeled using perturbation theory where the alpha nucleus must tunnel through the Coulomb barrier. This does a very good job of predicting alpha decays; hence the Coulomb force is unchanged for all heavy nuclei undergoing alpha decay. To see how it acts on the scale of smaller nuclei, you can go to scattering experiments. These allow us to probe the structure of protons and even resolve individual quarks. If the EM force behaved differently, those experiments would have to be reinterpreted. The tapestry of science is too tightly woven to hope that you can unravel one thread without having to make massive changes.

Scientific experts try to tell me how to do my job all the time. The problem is that they are frequently wrong and it takes a lawyer (and usually another expert) to make a judge understand that their explanations are wrong.

I find this quite surprising. What field of law do you practice?

My interest, and I think it has always been the goal of science, is in trying to understand nature in terms of more fundamental concepts... Nuclear physics tries to explain protons and neutrons in terms of more fundamental particles: quarks. Neutons and protons consist of two different combinatons of three quarks held together by an exchange of virtual particles. At this point we have trouble maintaining a conceptual framework because we have to rely on elaborate mathematical models to describe and predict what is happening. As we probe deeper into the nucleus the models become more elaborate rather than simpler. I am suggesting that perhaps there is a more fundamental principle or some simpler explanation that will tie it all together. I don't think I am alone.

I'm afraid I fail to see your point. Why exactly are we having trouble maintaining a conceptual framework? The mathematical models may be elaborate, but they do an excellent job of describing Nature. Right now the Standard Model reduces all of physics to some twenty-odd constants, and there are countless plans to reduce their numbers further by making a unified theory. Have you looked at such theories, like SU(5) or supersymmetry? In any event, there is no doubt that the strong force is here to stay, and will have to be included in any such searches. Since we have all done our best to give you reasons for the strong force's existence, the ball is in your court now: what evidence would be strong enough to convince you of its existence?

PS. I just realized that neutron stars might be a good place to see both gravity and strong nuclear forces at work. While I believe that the theories do a good job of predicting the properties of neutron stars (otherwise I'd know about it), I am not an astrophysicist, so I will have to defer this point.

 

[Nereid]

PS. I just realized that neutron stars might be a good place to see both gravity and strong nuclear forces at work. While I believe that the theories do a good job of predicting the properties of neutron stars (otherwise I'd know about it), I am not an astrophysicist, so I will have to defer this point.

I had a very nice post prepared, ready to post, then my browser crashed Will Bill give me a refund do you think?

We have modeled neutron stars, compared the results with observations, and the fit is very good. Unfortunately (or not!), we don’t have one in our neighbourhood, so we haven’t been able to perform controlled proton scattering experiments yet Indeed, the extent to which astronomy provides tests of a great deal of physics can sometimes be difficult to accept … I mean, a faint smudge of light in an image that’s full of other smudges is a gravitational lens, just as Uncle Al predicted?

Some highlights from models, which are based on General Relativity, the Standard Model (particle physics variety), as well as more pedestrian atomic physics, etc:
- there are well observed objects which have masses, densities, temperatures, surface compositions etc that match the models well (and few, if any, which don’t); pulsars are well-known examples
- from stellar evolution theory, we expect neutron stars to form under certain circumstances (e.g. ‘core collapse’ supernovae), and that’s just what we find; the Crab nebula is a good example
- the behaviour of neutron stars when mass is added – e.g. accretion from the other star of a close binary – is reasonably well studied, and observations match predictions closely; http://universe.gsfc.nasa.gov/press/images/rossi2000/
- research is under way into how waves in neutron stars can provide details of the internal structure of these gigantic nuclei, in a way similar to how seismology gives an idea of the internal structure of the Earth, and helioseismology the Sun
- indeed, studying neutron star may help us answer questions in high energy physics that aren’t possible to address here on Earth

 

[Andrew Mason]

If there is no strong force to provide the stability, then something else must do the job. It's as simple as that.

I agree.

There's nothing mysterious about the strong interaction. It's only mysterious to people who have not studied it.

All of physics is mysterious. We just reduce phenomena to fewer phenomena that we don't understand. That is the essence of all science. One should be cautious about saying these things are resolved. Planck's professor is a good example (he tried to dissuade Planck from taking up physics because all the great questions had been resolved - pre 1900).

How is energy converted to mass? How is it that our entire universe of matter and energy emerged from a point dozens of orders of magnitude smaller than a proton? Everything is mysterious at some level.

This is just silly. The energy well has to correspond to some potential. Don't you see that you're replacing the (well-understood) strong+weak+EM interaction with gravity and a mysterious energy well?

I am not replacing anything. I don't have a theory and I am not proposing one. I am just asking questions and suggesting that the nuclear force may not be a correct explanation of reality.

We measure the nuclear force indirectly. We measure energies. The fact is that the separation of a proton and neutron requires the creation of matter. That obviously requires energy. But perhaps the energy is not required to pull against an attractive force for the separation distance. Perhaps it is required to add mass to the separate proton and neutron. I am suggesting that the process of creating matter might be thought of as inhibiting separation.

We don't understand how matter is created. It obviously requires energy. Does it require that a force be applied to the proton for a particular distance? That is what I am asking. So far, no one seems to have come up with a good reason why it has to.

Where does this well come from? God?

Probably the same place that the universe came from. Are you suggesting that God can be ruled out?

Andrew Mason

 

[Andrew Mason]

No. The if the ball is dropped after the exchange, then the skaters continue moving towards each other. There has to be another exchange to stop the skaters.

Ok. Let's get this straight. There are two skaters at rest in the frame of reference of the ice, S1 and S2. S2 is holding a ball which is also at rest. S1 grabs the ball from S2 and pulls it toward himself accelerating the ball to a speed $v_b$. This results in momentum $p_b = m_b v_b$ of the ball and necessarily imparts an equal and opposite momentum to S1 toward S2. S1 moves toward S2 at a speed $v_{S1} = p_b/m_{S1}$. I think we are agreed to this point.

Then S1 stops the ball at his chest and drops it (if he doesn't stop it, the ball would keep going past him). You seem to be saying that $v_{S1}$ remains the same. I am saying that violates conservation of momentum. The reason is that in order to stop the ball, S1 has to absorb the ball's momentum $p_b$. Since that is equal and opposite to S1's momentum, this means that S1 stops.

But we don't even have to do that. We know that the momentum of the system is always 0 in the ice's frame of reference. If S2 is not moving and the ball is not moving, S1 can't be moving.

Will you please work out the calculation? It's quite simple. You have a skater carrying a ball, and they are both moving at speed v.

Why? How? This is not possible. They cannot possibly be moving at the same speed unless that speed is 0. See above.

If the skater drops the ball, the skater does not stop.

He does if he stops the ball and then drops it. I assume you mean by dropping the ball that the ball is stopped in the rest frame of the ice and does not go sailing off behind S1.

In fact, the skater moves faster, because of the reduced mass.

Not in this universe. And you think I need help with basic physics?

Please do a calucation, and you'll see that it does not work like this.

Calculations aren't required. It is just simple conservation of momentum. See above.

Please look up the definition of momentum. The ball need not be very heavy, if it is moving fast. I already explained this.

I don't need to look up the definition of momentum. Your comment that the skater speeds up if he reduces his mass is astounding really.

By "attraction" I mean that the skaters continue to move towards each other. While it is true that the center of mass of the entire system must not change its momentum, it is not true that the individual constituents of that system must stop moving. And no, the skaters need not have been skating prior to the exchange.

Well in your example if S2 and the Ball are not moving then S1 cannot be moving without violating conservation of momentum.

You are indeed struggling with the idea of momentum.

I am struggling with your concept of momentum. It is not Newton's.

First, you believe that only a very massive ball can impart an appreciable momentum transfer.

I never said that. I said that unless the ball was heavy, the skater would not move very far when the skater pulled it towards him. It has nothing to do with the speed at which he pulls it. It has to do with the location of the center of mass. That point can't change. If the ball is not heavy, the center of mass is very close to the skater. If the ball is very heavy, it is close to the ball, so the skater will move farther.

But that is wrong because p=mv, so a lightweight but fast moving ball can also impart such an impulse.

I have never said anything to suggest that I disagreed with that.

Second, you believe that a system with total momentum of zero implies that the momentum of all the constituents must also be zero. But that is also wrong.

I never said that. I said the center of mass can't move. The constituents can move all they want. But that point can't change.
You are really twisting what I have said here.

Once a momentum transfer takes place (as in, say, the exchange of a ball from one skater to another), the center of mass of the system is motionless despite the fact that each skater continues moving. If a momentum q is imparted to skater 1, and a momentum -q is imparted to skater 2, then the total momentum is conserved and the skaters continue on their merry way, towards each other.

You haven't got Skater 2 moving at all by Skater1 pulling the ball towards himself.

No, you're understanding my posts just fine. It's just that you need to brush up on basic physics. I'm sorry that you disagree, but it's true.

This is high school physics, Newton's laws. Your statement that the loss of mass by simply dropping the ball will cause S1 to speed up is patently absurd. I am sure you will realize that when you reread your post.

Andrew Mason

 

[Andrew Mason]

I find this quite surprising.

Ok, it may be a bit of an exaggeration.
One of the most frequent sources of error (e.g wrongful convictions) is incorrect expert evidence. Experts were found to say that hair and fibre could make a highly probable 'match', that bullets could be matched by their metallugical composition, that babies with heart problems can't have high digoxin levels naturally. A nurse was charged (and later discharged, fortunately) with murdering babies on the basis of bad science. Guy Paul Morin was wrongly convicted of murder on the basis of hair and fibre 'matches' (DNA later exhonerated him). Clayton Johnson was convicted because of experts who said his wife was murdered (later exhonerated by other experts and a whole body of other evidence). Hundreds, possibly thousands of cases based on the now discredited 'science' of bullet matching are now under review in the US.

A good example of 'expert' folly is in the acoustic experts who testified on the JFK assassination before the House Select Committee on Assassinations in 1978 and concluded that there were 4 shots. The fact that no one said that they were sure they heard 4 shots and 90% said there were exactly 3 (most of whom recalled the same pattern of shots 1...2...3) was completely ignored. The National Academy of Sciences later showed the errors. See: http://www.dufourlaw.com/jfk/shot_pattern_evidence.pdf

Even nobel physicist Luis Alvarez wrote an article in Physics Today advocating his new theory of jiggle effect (definitely an unproven technique which, in this case leads to conclusions that are inconsistent with the evidence). He did get some things right, mind you.

What field of law do you practice?

mainly litigation. see: http://www.dufourlaw.com/dufwho.htm#AM
For a good example of how an expert messed up a trial I was involved in and later corrected by the court of appeal, see: http://www.lawsociety.sk.ca/judgments/2003/Ca2003/2003skca40.pdf

Since we have all done our best to give you reasons for the strong force's existence, the ball is in your court now: what evidence would be strong enough to convince you of its existence?

Correct me if I am missing something, but the existence of the strong force is inferred from the binding energies that are observed for nuclear particles. Is there any other evidence of the strong force?

PS. I just realized that neutron stars might be a good place to see both gravity and strong nuclear forces at work. While I believe that the theories do a good job of predicting the properties of neutron stars (otherwise I'd know about it), I am not an astrophysicist, so I will have to defer this point.

I think you are right. If neutron star is as dense as the nucleus, then the nucleons in the neutron star are going to be within range of the strong nuclear force, if it exists. Now if we could only get a piece of a neutron star and see if it spontaneously flies apart...

There may be a way of testing the existence of the nuclear force if we could observe a star going through a gravitational collapse. As the density reached nuclear densities, there should be a significant release of energy as the nuclear force takes hold. That may be the theory behind the super nova explosion, I am not sure.
Andrew Mason

 

[quantumdude]

All of physics is mysterious. We just reduce phenomena to fewer phenomena that we don't understand.

OK fine, I'll amend my statement: The strong force is no more mysterious than any other interaction.

I am not replacing anything. I don't have a theory and I am not proposing one. I am just asking questions and suggesting that the nuclear force may not be a correct explanation of reality.

But that begs the question: Why does the Standard Model agree so well with experiment?

Probably the same place that the universe came from. Are you suggesting that God can be ruled out?

I'm saying that there is no need to introduce it. Likewise, there is no reason to introduce an energy well whose source is unknown.

 

[quantumdude]

This is high school physics, Newton's laws. Your statement that the loss of mass by simply dropping the ball will cause S1 to speed up is patently absurd. I am sure you will realize that when you reread your post.

I reread my posts, and now I see that I did not write what I intended to say. That's my fault, and I'm sorry for the confusion.

I meant for the exchange to be "sticky". That is, one skater actually rips the ball from the other's grasp, so that a fricitonal force develops between the skaters' hands and the ball. So, a force acts on each skater for a brief time interval. That sets both skaters into motion, and they will continue in that state of motion until acted on by a force.

Sorry, I've written this analogy so many times, in so many posts, that I got sloppy.

 

[Andrew Mason]

But that begs the question: Why does the Standard Model agree so well with experiment?

Probably because it was designed to explain experimental data. The Standard model made sense of a vast array of experimental data and reduced great complexity to something simpler. But even those who built the Standard Model don't really believe that it is the ultimate theory.

Murray Gell-Mann writes in his 1994 book "The Quark and the Jaguar" that the Standard Model is an ad hoc theory rather than a theory built on fundamental principles (like General Relativity, Newton's Laws, Maxwell's EM equations). It describes many interactions but does not relate them to each other. It requires arbitrary constants that are experimentally determined and not derivable from principle. And it does not include gravity. Despite all this, it is remarkably successful in explaining and predicting experimental data. It works. But that doesn't mean it is the last word as a theory.

I'm saying that there is no need to introduce it. Likewise, there is no reason to introduce an energy well whose source is unknown.

Until we know everything there is to know I wouldn't want to speculate on God's role in all of this.

I didn't introduce an energy well whose source is unknown. Empirically it has been shown to exist. Its source is unknown. I am just trying to understand what it represents. So far I see two possibilities: It could represent a strong force over a very short distance. Or it could represent something else.

Andrew Mason

 

[ZapperZ]

Probably because it was designed to explain experimental data. The Standard model made sense of a vast array of experimental data and reduced great complexity to something simpler. But even those who built the Standard Model don't really believe that it is the ultimate theory.

Murray Gell-Mann writes in his 1994 book "The Quark and the Jaguar" that the Standard Model is an ad hoc theory rather than a theory built on fundamental principles (like General Relativity, Newton's Laws, Maxwell's EM equations). It describes many interactions but does not relate them to each other. It requires arbitrary constants that are experimentally determined and not derivable from principle. And it does not include gravity. Despite all this, it is remarkably successful in explaining and predicting experimental data. It works. But that doesn't mean it is the last word as a theory.

Apparently, this thing will simply not go away...

Again, your information is a bit dated like your Feynman text. While the Standard Model came into being as a phenomenological model (as most anything that is new), it has outgrown that status! It has made several predictions that have been verified to be true. There are sound theoretical description that can verify many of its components. You would have known this had you studied something like Perkin's High Energy Physics text. So saying that the Standard Model is nothing more than an "ad hoc" theory in its CURRENT form is like saying the Maxwell equation is nothing more than a collection of experimental observation. Theories and descriptions evolve! 1994 may have been a good year, but man, that is ancient history in many areas of physics.

There are plenty of indications that the Standard Model isn't complete. No high energy physicist in their right mind would even claim that. However, these indications do not come from what you have in mind, nor based on what you have suggested.

May I also suggest that you do not try to counter a physics argument with quotations? Not only are quotations often taken out of context (Einstein's "knowledge-imagination" is a prime example), but also they mean nothing in a physics discussion of CONTENT. Open any physics journals and you will not see a rebuttal or a comment on a physics paper done simply via quotations.

I'm curious. Are you still hanging on to this question: "Can anyone explain to me why gravity would not be a significant force on the 'surface' of a proton or neutron?" In other words, are you still under the false impression that GRAVITY can produce a significant force in nuclear binding?

Zz.

 

[marlon]

A very nice question to you Andrew...from our most friendly science advisor, who is always in "the very best of moods"...


marlon

 

[Andrew Mason]

I'm curious. Are you still hanging on to this question: "Can anyone explain to me why gravity would not be a significant force on the 'surface' of a proton or neutron?" In other words, are you still under the false impression that GRAVITY can produce a significant force in nuclear binding?

I never said that gravity explained nuclear binding. I just pointed out that gravity on the 'surface' of a nucleon would be sufficient to keep nucleons together - ie. a little separation would cause the nucleons to return together quickly. The nuclear binding energy (of, say, a deuteron) is a different matter. It can't be explained by gravity as we know it, and I never suggested it was.

The atoms of $H_2$ can escape their EM binding energy 'well' without adding mass to the protons or electrons that comprise those atoms. The nucleons in a nuclear binding energy 'well' can only escape by adding mass to those nucleons. I am suggesting that the nuclear binding energy (or mass creation energy) can be thought of as a kind of barrier to exit rather than a force that keeps the nucleons together. If that is the case, then gravity could be the only force inside that barrier.

Andrew Mason

 

[quantumdude]

Probably because it was designed to explain experimental data.

OK, now we're getting somewhere. Now all I have to do is get you to accept that fitting the data is a good reason to accept a theory, rather than to reject it.

The Standard model made sense of a vast array of experimental data and reduced great complexity to something simpler. But even those who built the Standard Model don't really believe that it is the ultimate theory.

Of course they don't, and I don't believe that it's the ultimate theory either. But you can be assured that the next step in the process will not involve turning our backs on the Standard Model. In fact, it will most certainly be a requirement of the next theory that it include the Standard Model as a special case.

Murray Gell-Mann writes in his 1994 book "The Quark and the Jaguar" that the Standard Model is an ad hoc theory rather than a theory built on fundamental principles (like General Relativity, Newton's Laws, Maxwell's EM equations). It describes many interactions but does not relate them to each other. It requires arbitrary constants that are experimentally determined and not derivable from principle. And it does not include gravity. Despite all this, it is remarkably successful in explaining and predicting experimental data. It works. But that doesn't mean it is the last word as a theory.

Agreed.

Until we know everything there is to know I wouldn't want to speculate on God's role in all of this.

And there is no need to. Furthermore, there is no need to speculate on the role of a mysterious energy well that comes from nowhere and corresponds to nothing we know of. Do you agree?

I didn't introduce an energy well whose source is unknown. Empirically it has been shown to exist. Its source is unknown. I am just trying to understand what it represents. So far I see two possibilities: It could represent a strong force over a very short distance. Or it could represent something else.

Here's where I see this going.

You think that the strong force doesn't exist and that the EM force mysteriously turns off--for no apparent reason--at subnucleonic distances. In place of that you think that gravity + a potential well is responsible. But the gravitational interaction that is necessary to account for experimental data could not possibly be the same one that we know of classically. Therefore, we are looking at a gravitational interaction that is nothing like Newton's or Einstein's conception of it. We are looking at an interaction that behaves altogether differently from Newton's or Einstein's gravity at a very short distance, that holds the nucleus together, and that accounts for the observed hadron spectra.

I contend that you are simply attaching the label "gravity" to what is more commonly known as "the strong interaction".

 

[ZapperZ]

I never said that gravity explained nuclear binding. I just pointed out that gravity on the 'surface' of a nucleon would be sufficient to keep nucleons together - ie. a little separation would cause the nucleons to return together quickly.

But you can only say this if you complete turn OFF the coulomb force. What makes you think it is valid for you to extrapolate gravity up to that scale, and yet you keep complaining that EM fields should not work there? If you accept that gravity works the same way all the way to nuclear scale, then you should be fair and also invoke EM fields too! Then coulombic forces would have severely overwhelm the puny gravitational forces by comparison! Several people have already given you the order of magnitude difference between the two! And don't tell me that we have no experimental data that EM forces should work at that scale, because that argument can be used against your gravity also, which would then make your whole point moot.

The atoms of $H_2$ can escape their EM binding energy 'well' without adding mass to the protons or electrons that comprise those atoms. The nucleons in a nuclear binding energy 'well' can only escape by adding mass to those nucleons. I am suggesting that the nuclear binding energy (or mass creation energy) can be thought of as a kind of barrier to exit rather than a force that keeps the nucleons together. If that is the case, then gravity could be the only force inside that barrier.

I have no idea what you just said here or why it is even relevant. Atoms of H2 can "escape" from a "binding energy well"? Hello? I was talking about NUCLEAR binding, not MOLECULAR binding. H2 is a MOLECULE, and thus, each H atom have a molecular binding with the other H atom. This is NOT a nuclear binding energy. Please don't change or confuse the subject.

Zz.

 

[Andrew Mason]

But you can only say this if you complete turn OFF the coulomb force. What makes you think it is valid for you to extrapolate gravity up to that scale, and yet you keep complaining that EM fields should not work there? If you accept that gravity works the same way all the way to nuclear scale, then you should be fair and also invoke EM fields too!

Gravity appears to be different than the other forces. Nothing in EM or the Standard Model accounts for gravity. Only General Relativity does that. The principle of equivalence says that gravity and inertia can be considered equivalent, so gravity can be looked at as a pseudo-force or a curvature in space time. There is no evidence that space-time has quantum-like discreteness, unlike EM phenomena and the nucleus. So there is no reason to believe that gravity is any different at small distances. EM theory assumes point charges but we know that the proton is not a point charge.

According to the Standard Model, coulomb force is associated with the + and - 2/3 spin of quarks. The model does not explain how the coulomb force results from that and does not predict the nature of force that is created (perhaps my understanding of this is incorrect, in which case I would welcome correction). We don't really know where it begins. We only know that it is associated with quarks and exists in some region outside the proton, perhaps down to the quark level, perhaps not. Gravity, on the other hand, has no such limit because it is not so much a physical property of matter as it is a property of the space-time environment.

Then coulombic forces would have severely overwhelm the puny gravitational forces by comparison! Several people have already given you the order of magnitude difference between the two! And don't tell me that we have no experimental data that EM forces should work at that scale, because that argument can be used against your gravity also, which would then make your whole point moot.

I have explained why gravity would not turn off inside the nucleus. What evidence do we have that EM forces actually exist between protons in a He nucleus?

I have no idea what you just said here or why it is even relevant. Atoms of H2 can "escape" from a "binding energy well"? Hello? I was talking about NUCLEAR binding, not MOLECULAR binding.

Of course H atoms bind with EM molecular binding forces. I said "EM binding energy well" to distinguish it from nuclear binding energy.

My point was that there appears to be a fundamental difference between the two. Molecules can be separated without adding mass to the nuclei or electrons that compose those molecules. Nuculeons cannot be separated without adding mass to the nucleons.

H2 is a MOLECULE, and thus, each H atom have a molecular binding with the other H atom. This is NOT a nuclear binding energy. Please don't change or confuse the subject.

I was not trying to change the subject. I was just pointing out that separation of atoms in a molecule (which derives from a $1/r^2$ force and therefore a $-1/r$ energy potential) is very different from the separation of nuclear particles. I point out that one difference is that overcoming the nuclear potential results in adding mass to the separated parts (nucleons) while overcoming the EM potential does not add mass to the separated parts. While the energy required to separate atoms is the due to the need to apply a force over a distance, the energy required to separate nuclei is needed to create mass. Perhaps instead of looking at the nuclear binding energy as a continuous force between nucleons, we could look at it as a 'barrier' to separation. The analogy would be to a can of beans. The can prevents them from escaping. But it does not create a continuous force between the beans.

I am merely suggesting that if we looked at the nuclear potential in these terms, we would not need to invent a force that is enormous within a tiny distance (1 f.) and is effectively 0 outside that distance, and becomes repulsive at very short distances so as not to squish the nucleons.

Andrew Mason

 

[quantumdude]

There is no evidence that space-time has quantum-like discreteness, unlike EM phenomena and the nucleus. So there is no reason to believe that gravity is any different at small distances.

Yes, there is reason to think that quantum gravity is the correct path. You note general relativity, but fail to note that GR and QFT contradict each other. They can't both be right, and there is little doubt that a correct description of gravity will lead to a quantized theory.

According to the Standard Model, coulomb force is associated with the + and - 2/3 spin of quarks.

The electric charges are +1/3 and -2/3. All quarks have the same spin: 1/2.

The model does not explain how the coulomb force results from that and does not predict the nature of force that is created (perhaps my understanding of this is incorrect, in which case I would welcome correction).

As I noted in an earlier post, Coulomb's law is derivable from QFT. It is reducible to electric charges in motion. What the Standard Model does not explain is the existence of charges. But then again, neither does any other theory.

We don't really know where it begins. We only know that it is associated with quarks and exists in some region outside the proton, perhaps down to the quark level, perhaps not. Gravity, on the other hand, has no such limit because it is not so much a physical property of matter as it is a property of the space-time environment.

I have explained why gravity would not turn off inside the nucleus. What evidence do we have that EM forces actually exist between protons in a He nucleus?

We have yet to see a compelling reason to think that the EM interaction should switch off at any distance. And we have plenty of evidence in favor of the other side, in that all predictions of the Standard Model have been verified.

My point was that there appears to be a fundamental difference between the two. Molecules can be separated without adding mass to the nuclei or electrons that compose those molecules. Nuculeons cannot be separated without adding mass to the nucleons.

That's not true of molecules. There is a slight increase in mass.

I am merely suggesting that if we looked at the nuclear potential in these terms, we would not need to invent a force that is enormous within a tiny distance (1 f.) and is effectively 0 outside that distance, and becomes repulsive at very short distances so as not to squish the nucleons.

So instead, we invent a sourceless potential well to keep the nucleons together because gravity is not strong enough to keep them in, is that it?

I'm sorry, but this idea of yours hasn't a leg to stand on. The simple fact of the matter is that we would have to continue using the Standard Model, because there's not a single quantitative prediction here. And besides, you'd have to tailor the energy well just so that it fit the observed spectrum of hadrons. Whereas with the Standard Model, we have the following few ingredients:

1. Canonical quantization.
2. Special relativity.
3. A gauge group.

From just these 3 things, all the predictions follow.

 

[ZapperZ]

Your reply here is laced with ignorance and mistakes, and you seem to somehow have the ability to state all of the statements below as IF you have a complete knowledge of what you are stating. Nowhere in the immediate quote below was even a question or any sense of uncertainty of what you are stating:

Gravity appears to be different than the other forces. Nothing in EM or the Standard Model accounts for gravity. Only General Relativity does that. The principle of equivalence says that gravity and inertia can be considered equivalent, so gravity can be looked at as a pseudo-force or a curvature in space time. There is no evidence that space-time has quantum-like discreteness, unlike EM phenomena and the nucleus. So there is no reason to believe that gravity is any different at small distances. EM theory assumes point charges but we know that the proton is not a point charge.

According to the Standard Model, coulomb force is associated with the + and - 2/3 spin of quarks. The model does not explain how the coulomb force results from that and does not predict the nature of force that is created (perhaps my understanding of this is incorrect, in which case I would welcome correction). We don't really know where it begins. We only know that it is associated with quarks and exists in some region outside the proton, perhaps down to the quark level, perhaps not. Gravity, on the other hand, has no such limit because it is not so much a physical property of matter as it is a property of the space-time environment.

For someone who keeps insisting that all theories are subject to being challenged and being changed, you are quite arrogant in what you think gravitational theory should be and what it should not be. While GR has a number of verifications, in terms of degree of certainty, it has a LESS degree of certainty that classical E&M and QED. Now read that again - GR, which you are putting ALL your faith in, has a lower degree of certainty than classical E&M and QED. Furthermore, and pardon me for saying that, but I do not believe you even have a clue the complex theory of GR, much less are able to judge its validity.

Secondly, + and - 2/3 spin of quarks?!

Thirdly, you have this unhealth obsession with so-called "point charge". If you have studied physics at any considerable level, you would have noticed that the classical electrostatic description has an equivalent form to the classical gravitational description. There is a gauss's law equivalent for gravitational field, for example. Every single description for an electrostatic field, there is an identical equivalent for a gravitational field (except for the absence of an repulsive force). Thus, gravitational force ALSO considers the mass being acted upon as point mass sources! Someone should have clearly pointed this out in your original "derivation" of gravitational force. Don't believe me, go double check what you did... you put ALL of the mass of the proton to be at the radius of another proton. Ignoring the obvious fact that you have two protons overlapping each other already, you yourself are doing the very thing you are criticizing, lumping the mass of an object into a point mass.

So get over this "point charge" problem already.

I have explained why gravity would not turn off inside the nucleus. What evidence do we have that EM forces actually exist between protons in a He nucleus?

What evidence that it doesn't? We have no description or evidence that EM forces can just simply disappear. It is YOUR responsibility to prove that your "new imagination" has a valid impetus to be considered other than just something you thought of out of ignorance.

Of course H atoms bind with EM molecular binding forces. I said "EM binding energy well" to distinguish it from nuclear binding energy.

My point was that there appears to be a fundamental difference between the two. Molecules can be separated without adding mass to the nuclei or electrons that compose those molecules. Nuculeons cannot be separated without adding mass to the nucleons.

I was not trying to change the subject. I was just pointing out that separation of atoms in a molecule (which derives from a $1/r^2$ force and therefore a $-1/r$ energy potential) is very different from the separation of nuclear particles. I point out that one difference is that overcoming the nuclear potential results in adding mass to the separated parts (nucleons) while overcoming the EM potential does not add mass to the separated parts. While the energy required to separate atoms is the due to the need to apply a force over a distance, the energy required to separate nuclei is needed to create mass. Perhaps instead of looking at the nuclear binding energy as a continuous force between nucleons, we could look at it as a 'barrier' to separation. The analogy would be to a can of beans. The can prevents them from escaping. But it does not create a continuous force between the beans.

I am merely suggesting that if we looked at the nuclear potential in these terms, we would not need to invent a force that is enormous within a tiny distance (1 f.) and is effectively 0 outside that distance, and becomes repulsive at very short distances so as not to squish the nucleons.

Andrew Mason

This last set of paragraphs are a complete mystery to me. What EXACTLY is this about? Adding mass and not adding mass?? Applying force over a distance? Huh??! I have to add mass to separate nucleons? Tell me where I am adding mass in an alpha decay? And if you are somehow thinking that separated daughter nucleons ALWAYS have a higher total mass than the original parent nucleus, I have a fission reactor I want you to meet.

You are not suggesting anything. You are trying to ignore a huge part of physics that you have no clue on (QCD), and trying to replace it with your faulty physics knowledge. In the process, you are doing the exact same thing you are finding faults in with EM and QED. But what is even more appaling is that you are STILL insisting there is some validity in your faulty idea inspite of (i) your admission of lack of any serious knowledge in the matter you are talking about and (ii) the REPEATED explanation of those who are more knowledgeable than you on why your idea is wrong.

In the end, I find it ironic that you would spend time quoting Gell-Mann for something that suits your needs, and yet you blatantly reject his most significant contribution - the quarks and how they interact. I hate to think that this is how you practice your profession.

Zz.

 

[anti_crank]

I find it unbelievable that this thread is still going, and it raises serious doubts in my mind as to whether any progress is being accomplished. For the last time, I will summarize the main points:

-EM waves obey Maxwell's equations at all known ranges, including well past nuclear range. Hence it is contradictory to assume that classical forces from electrodynamics break down at such scales while the Maxwell equations stand since they come from the same mathematics.
-Scattering experiments confirm that the EM force works as expected. In fact, accelerators would not work if classical EM would break down at those scales/energies. In practice, we routinely accelerate particles to high energies (the LHC at CERN can accelerate protons to 100GeV) without any surprises.
-We know from scattering experiments that nucleons (protons/neutrons) have constituents, whose fractional charges can be measured and agree with the quark model
-The strong force model explains the observed spectrum of mesons and baryons beautifully. Heavy quark systems can be solved with the Schroedinger equation and an approximate, single-gluon exchange radial potential. The spectrum of allowed states for such systems matches observations very well.
-A force exists between nucleons and their constituents that allows certain decays which cannot be otherwise explained. The lifetimes are too small for the decays to be either electromagnetic or weak. We know this because lifetimes are inversely proportional to couplings. Gravity - unless strengthened immensly - is nowhere near the right coupling strength to allow such things.
-Gravity is negligible on the nuclear range, unless radical changes are made to it. Such changes are not warranted by any known results, and would make it a downright ugly theory. Try finding the ground state, using either Schroedinger eqn or Bohr quantization rules if Schr. is too hard, for a system of two heavy quarks bound by the gravitational potential. What's the expected radius - anywhere near the size of nuclei?
-Gluons are one prediction of QCD. Their existence, as well as some properties, can be inferred from three-jet events in accelerators and deep nuclear scattering experiments. The latter indicate that over 50% of a proton's momentum is carried by neutral (non-charged) constituents.
-Regarding neutron stars: see Nereid's post.

At this point, let me make an analogy that should make things clear. This problem has already been in the court of science, a court comprised of all scientists, past and present, who have dealt with this problem. Judgement has been passed by a large majority in favor of the strong nuclear force as presently known to provide the best explanation for the structure of nucleons. Since you've not provided any reasons for appeal that carry any merit upon in depth examination, the request for an appeal is denied. It's very possible for forensic experts to be wrong, and it simply goes to show the need to have multiple and independent experts analyse the problem and voice their opinion. Science is not dogmatic or authoritarian as is often believed by the general public, but relies on concrete evidence from experiments. This test was passed by the strong force, and it makes much less difference whether the experiments came before or after the theory than whether the experiments match the theory at all.

 

[quantumdude]

I'd like to thank everyone for their contributions, and ask that we move on.