Why Gravity is Significant in Proton & Neutron Nuclei

[ZapperZ]

I'll admit my study of physics is rather out of date. I took a couple of courses on quantum physics but most of my understanding of the subject came from Richard Feynman. I will give you a quote from Feynman's Lectures on Physics (Feynman, of course, won the Nobel Prize for his work in quantum electro-dynamics, so I think that he understood QED fairly well):
Vol 1, page 12-12,

"12-6 Nuclear Forces:...

These forces are within the nuclei of atoms, and although they are much discussed, no one has ever calculated the force between two nuclei and indeed at present there is no known law for nuclear forces. These forces have a very tiny range which is just about the same as the size of the nucleus, perhaps $10^{-13}$ centimeter. With particles so small and at such a tiny distance, only the quantum-mechanical laws are valid, not the Newtonian laws. In nuclear analysis we no longer think in terms of forces, and in fact we can replace the force concept with a concept of the energy of interaction of two particles a subject that will be discussed later. Any formula that can be written for nuclear forces is a rather crude approximation which omits many complications; one might be somewhat as follows: forces within a nucleus do not vary inversely as the square of the distance but die off exponentially over a certain distance r, as expressed by $F = (l/r^2) exp(-r/r_0)$ where the distance $r_0$ is of the order of $10^{-13}$ centimeter. In other words, the forces disappear as soon as the particles are any great distance apart, although they are very strong within the $10^{-13}$ centimeter range. So far as they are understood today the laws of nuclear force are very complex: we do not understand them in any simple way and the whole problem of analysing the fundamental machinery behind nuclear forces is unsolved. Attempts at a solution have led to the discovery of numerous strange particles, the $\pi$ mesons, for example, but the origin of these forces remains obscure."


If I can start by updating this paragraph, I might be able to stop annoying everyone with my naive questions. For example, have we been able to measure the force between a proton and a neutron in, say, the deuterium nucleus? Have we been able to measure the nuclear force between two protons in, say, the He nucleus?

Andrew Mason

If you are any more out of date than this, you would have to read works chiselled in stone tablets. It might be helpful to read the publication dates on this.

At the time Feynman wrote this, the pion (or pi meson) was thought to be the mediator of the strong force based on the Yukawa theory. It isn't. We know MORE (lots more) about it now since the present-day development has clearly point out the gluons as this mediator.

You also must keep in mind that you are trying to comprehend something that is highly complex. Even as someone who is a trained physicist but with expertise in condensed matter, I would never be silly enough to come up to another nuclear physicist/high energy physicist and start spewing out my own theory about nuclear forces, even though my knowledge of nuclear physics and high energy physics are more than what a typical quack has. Are you able to comprehend the idea that protons and neutrons do not maintain their rigid indentity when they are part of a nucleus? Can you understand the parton structure and how the so-called "color forces" interact between them? What about the tantalizing hint at the observation of the quark-gluon plasma at RHIC?

These may appear to you to be a disjointed set of information that have nothing to do with what you're asking, but they are EXACTLY the "evidence" that you are asking for. While quantum mechanics isn't JUST the Schrodinger equation or the uncertainty principle, the same way QCD isn't JUST about quarks and the standard model. It is about a whole body of knowledge in dealing with the strong interaction. You can't just pick one thing and ignore the rest because there is a whole zoo of consequences via the prediction of the existence of the strong interaction. These consequences are the ones we observe and verify via experiments that confirm the validity of QCD. And we continue to do that with better accuracy and high degree of certainty.

Zz.

 

[Andrew Mason]

If you are any more out of date than this, you would have to read works chiselled in stone tablets. It might be helpful to read the publication dates on this.

I am not assuming that his lectures (ca. 1961) are a source of up-to-date information. But his explanations of the concepts are very useful.

You also must keep in mind that you are trying to comprehend something that is highly complex. Even as someone who is a trained physicist but with expertise in condensed matter, I would never be silly enough to come up to another nuclear physicist/high energy physicist and start spewing out my own theory about nuclear forces, even though my knowledge of nuclear physics and high energy physics are more than what a typical quack has.

I don't think I am giving you my own theory about nuclear forces. I am a long way from understanding the elementary stuff, let alone developing a theory. I am just asking questions.

Are you able to comprehend the idea that protons and neutrons do not maintain their rigid indentity when they are part of a nucleus?

This is actually the purpose of some of my questions. We can certainly talk about coulomb forces between separate protons. How do we really know that these same coulomb forces exist between protons in the nucleus?

Can you understand the parton structure and how the so-called "color forces" interact between them? What about the tantalizing hint at the observation of the quark-gluon plasma at RHIC?

I am sure I could... in another lifetime. I confess I do not really understand how an exchange of elementary particles between protons / neutrons creates an attractive force.

These may appear to you to be a disjointed set of information that have nothing to do with what you're asking, but they are EXACTLY the "evidence" that you are asking for. While quantum mechanics isn't JUST the Schrodinger equation or the uncertainty principle, the same way QCD isn't JUST about quarks and the standard model. It is about a whole body of knowledge in dealing with the strong interaction. You can't just pick one thing and ignore the rest because there is a whole zoo of consequences via the prediction of the existence of the strong interaction. These consequences are the ones we observe and verify via experiments that confirm the validity of QCD. And we continue to do that with better accuracy and high degree of certainty.

I do appreciate your help.

Andrew Mason

 

[humanino]

Please read [thread=41110]this thread[/thread] about nuclear interactions.

Andrew, I think you did not take time to read [thread=41110]this thread[/thread] which is short, and which might help you asking questions.

 

[quantumdude]

A simple calculation should reveal the reason that this gravity idea cannot be right. Take a 2-nucleon system, and a typical nucleon radius of about 1 fermi (that's 10^-15m), and calculate the gravitational potential energy. I got something on the order of magnitude of 10^-30eV, which is far, far below the scale of nuclear binding energies (which are on the order of 1 to 10² MeV).

What more could you want?

 

[Andrew Mason]

Andrew, I think you did not take time to read [thread=41110]this thread[/thread] which is short, and which might help you asking questions.

I am trying to understand the nature of the forces within the nucleus. It seems to me that we have several consistent mathematical models which, together, allow us to predict the behaviour of fundamental constituents of matter and energy very accurately. It is not necessarily the case, however, that a consistent model describes reality. It may be just a helpful device to work with. The concept of a 'particle' for example, when speaking of fundamental particles, is just a mental device that allows us to think about mathematical wave functions as discrete entities. We know that these are not particles in the classical sense.

The 'particle' is still a very useful model to use, just as lines of force is a useful concept for mathematically modelling the magnetic and electric field. We don't pretend that they really exist. The concept of the exchange of virtual particles creating a force between quarks, and the residual effect of this exchange creating strong forces between protons and neutrons (perhaps because protons and neutrons in close proximity share , seems to me to be a similar device. If it works to explain behaviour, it is a very useful model to use. But that does not mean it is the only possible way of looking at it.

Gravity can be conceived as a attractive force that one particle exerts on another particle by virtue of their respective masses. Newton provided a very consistent mathematical model for gravity, which is still very useful. Einstein provided another very different mathematical model which has also been very useful. Einstein's model, however, involves a reexamination of our concepts of distance and time and the essence of matter itself. Einstein's theory of general relativity is, in that sense, the more fundamental model.

Now it may be that gravity has very little to do with the structure of the nucleus at the level that we are probing now. But I am not so sure that will be the case as we probe more deeply.

Now, dealing with the concept of a force created by the exchange of virtual particles, I have a conceptual diffculty here. How is it that such an exchange is attractive? Doesn't an exchange of particles carry momentum that would tend to move the sender and recipient farther apart?

Andrew Mason

 

[Orion1]

Classical Consistency...



In Classical Quantum Electrodynamics, the Fine Structure Constant is a classical tool used to measure the relative strength between any force and that of the classical Strong Nuclear Force.

Given this classical model which approximates for any two particles on a nuclear scale, the following equations results. (note that these obey the 'Andrew Model')

Classical Quantum Electrodynamics gravitational Fine Structure Constant:
$$\propto_g = \frac{Gm_p^2}{\hbar c}$$
$$m_p$$ - proton mass

Classical Quantum Electrodynamics Electromagnetism Fine Structure Constant:
$$\propto_e = \frac{K_e q^2}{\hbar c}$$
$$K_e$$ - Coulomb's proportionality constant
$$q$$ - proton charge

Andrew, based upon these equations, what are the SI (International Standard) units for $$\propto_e$$ and $$\propto_g$$?

Andrew, based upon these equations, what is the relative difference in magnitude between $$\propto_e$$ and $$\propto_g$$?

Andrew, how do these magnitudes compare with that of the classical Strong Nuclear Fine Structure Constant?

These equations obey the original 'Andrew Model'. (post #1)



"The fine structure constant measures the strength of the electromagnetic force that controls how charged elementary particles (such as electrons and photons) interact."...

Reference:
http://whatis.techtarget.com/definition/0,,sid9_gci866284,00.html

 

[selfAdjoint]

In Classical Quantum Mechanics, the Fine Structure Constant is a classical tool used to measure the relative strength between any force and that of the classical Strong Nuclear Force.

I think you'd better look up the definition of the fine structure constant again.

 

[quantumdude]

Now it may be that gravity has very little to do with the structure of the nucleus at the level that we are probing now. But I am not so sure that will be the case as we probe more deeply.

It is the case that gravity has very little to do with it. As I said in my last post, the gravitational potential energy between 2 nucleons that are separated by any acceptable nuclear radius (as determined by scattering expeirments) cannot possibly account for the binding energy between them (as determined by fission experiments). This idea can be rejected on the basis of a "back of the envelope" calculation.

Now, dealing with the concept of a force created by the exchange of virtual particles, I have a conceptual diffculty here. How is it that such an exchange is attractive? Doesn't an exchange of particles carry momentum that would tend to move the sender and recipient farther apart?

Imagine that 2 ice skaters are the particles, and the force carrier is a basketball. If they exchange it such that one skater throws it to the other, then indeed the force is repulsive. But if they exchange it in such a way that one grabs it from the other, then the two are drawn together, and the force is attractive.

 

[Ian]

When making gravitational calculations on atomic and nuclear scales, why use the magnitude of G as quoted in the original post?

There is no proof that it is correct to use the 'solar scale' value of G at the smaller scale, neither has any physicist ever given a theoretical definition to Newton's constant that adequately predicts G.

However, G has been defined as the 'torsion' of spacetime according to quantum theory, therefore matter of a higher density should produce a greater compression of the vacuum. Since nuclear matter has a far greater density than the sun or earth, the distortion of the vacuum in the vicinity of nuclear matter must be far greater than we observe at the solar scale and G at that tiny scale must be much greater than we assume.

If you increase the observed value of G by a factor equal to the perceived difference in strength between gravitational and electric forces in atoms (and use this in gravitational calculations) then the electric and gravitational mathematical expressions all become unified.

Therefore the easiest and only way to unify Gravitation and electromagnetism is to show that G changes with matter density, or to produce a competent theoretical model that predicts or explains how G changes with increasing density.
(a simple re-working of Einstein's flat-sheet + ball analogy will do it, explain G that is)

 

[humanino]

When making gravitational calculations on atomic and nuclear scales, why use the magnitude of G as quoted in the original post?

This is obviously a very relevant objection, with which I fully agree. We have no clue of gravity at small scales, and we wish we had !
Yet :

However, G has been defined as the 'torsion' of spacetime according to quantum theory

Could you be more precise, or elaborate ?
Torsion is a well defined quantity already in differential geometry, it is the non-symmetrical part of the connection coefficients (Christoffel symbols) (torsion in MathWorld)
$$T(u,v)=\nabla_uv-\nabla_vu-[u,v]$$
and it is assumed zero in Einstein's theory :
[URL='https://www.physicsforums.com/insights/author/john-baez/']John Baez on zero torsion[/url]

 

[Nereid]

On the one hand, we have a theory (or set of mutually consistent theories) which account for ALL the experimental and observational results, some with breath-taking degrees of accuracy.

On the other hand, we have some speculation and hand-waving, a few curious and possibly interesting 'what if?'s.

On the third hand (us .pas omoH sentient sgnieb from htraE are cursed/blessed with more sdnah than Homo sap. ), our two best (classes of) theories - GR and QM - cannot both be, in domains far, far beyond what we've been able to test to date.

Your mission, should you choose to accept it, is to convert the hand-waving into the outline of a sketch of a hypothesis, and show - to even 5 OOM (I'm feeling generous today) - that it is consistent with relevant observational results.

 

[marlon]

At the time Feynman wrote this, the pion (or pi meson) was thought to be the mediator of the strong force based on the Yukawa theory. It isn't. We know MORE (lots more) about it now since the present-day development has clearly point out the gluons as this mediator.

Just to be accurate...

The pions are indeed not the strong force mediators as originally assumed by Yukawa. The strong force mediators are elementary particles themselves : the gluons. These gluons make sure the quarks constituting a meson or a baryon are all bound together so the meson (quarkdoublet) and the baryon (quarktriplet) does not "fall" apart. The lightest meson is the pion (quark anti-quark combination) which is NOT an elementary particle yet it DOES mediate a "part" of the strong force. I am referring to the socalled residual strong force that holds atomic nuclei together...

Also keep in mind that QCD describes at best the behavior of colour-confinement, although this problem is not yet "solved". Many propositions exist among theoretical physicists like the dual abelian higgs-model using the nice magnetic monopoles introduced by Dirac. Also keep in mind that gluons can interact with each other via the colour-confinement (although not every gluon exhibits a colour; meaning they can be colour-neutral), which is a big difference with the mediators of the EM-force ie the photons...

regards
marlon

 

[ZapperZ]

When making gravitational calculations on atomic and nuclear scales, why use the magnitude of G as quoted in the original post?

There is no proof that it is correct to use the 'solar scale' value of G at the smaller scale, neither has any physicist ever given a theoretical definition to Newton's constant that adequately predicts G.

However, G has been defined as the 'torsion' of spacetime according to quantum theory, therefore matter of a higher density should produce a greater compression of the vacuum. Since nuclear matter has a far greater density than the sun or earth, the distortion of the vacuum in the vicinity of nuclear matter must be far greater than we observe at the solar scale and G at that tiny scale must be much greater than we assume.

On the other hand, what could be the possible impetus to consider that G might be different at those scales? I haven't seen any. In fact, going by recent trends in the latest set of experimental measurement of G to test the Arkani-Hamed hypothesis of millimeter scale compaction, no deviation has been found up to 10 micrometer scale![1] Couple this with an earlier measurements [2], and the recent report from the 2004 APS April meeting from the U. of Mainz on "neutron bouncing" experiment, there is clearly every indication that gravity that we know of at the macroscopic scale still works the same way at the microscopic scale. Granted that these scales are still not within the nuclear length scales, but if we simply go by experimental observations and trends, there are ZERO indications that G would deviate from the known value.

Zz.

[1] J. Chiaverini et al., PRL v.90, p.151101 (2003).
[2] PRL v.86 , 1418 (2001); J.C. Long et al., Nature v.421, p.922 (2003).

 

[Andrew Mason]

It is the case that gravity has very little to do with it. As I said in my last post, the gravitational potential energy between 2 nucleons that are separated by any acceptable nuclear radius (as determined by scattering expeirments) cannot possibly account for the binding energy between them (as determined by fission experiments). This idea can be rejected on the basis of a "back of the envelope" calculation.

Could the binding energy not simply be stored in the form of matter rather than a force x distance concept of potential energy? The pairing of a proton and a neutron is a very stable configuration from an energy perspective. But when enough energy is added so that the particles are lifted out of that deep energy well, the result is a conversion of some of that matter back into energy.

Do we really have to be wedded to a concept of a 'force' within the nucleus? I say this knowing full well that there is probably something quite basic that I am missing so please be gentle on me.

Imagine that 2 ice skaters are the particles, and the force carrier is a basketball. If they exchange it such that one skater throws it to the other, then indeed the force is repulsive. But if they exchange it in such a way that one grabs it from the other, then the two are drawn together, and the force is attractive.

Or perhaps hockey players grabbing a puck ... but I appreciate your analogy. As I understand your analogy, the skaters would only get closer together if the other was still holding onto the ball. Otherwise, if it is just the momentum of the ball that moves the 'grabber' toward the 'grabbee', the two don't get very close - not unless the ball is much more massive than the player. So that begs the question: what is the skater/quark holding onto the ball/gluon with? Would you not have to assume some additional 'sticky' force there between the ball/gluon and the skater/quark?

I have tried to wrap my mind around virtual particles with negative momentum traveling faster than c in a cloud of uncertainty to explain the nuclear force. I am getting the impression that trying to give a physical meaning for what is essentially a mathematical solution to a wave function is probably hopeless. Forgive my naiveté in thinking that there must be other, as yet undiscovered, model or fundamental principle that we are missing in all of this. But I find it all very fascinating.

Andrew Mason

 

[ZapperZ]

Could the binding energy not simply be stored in the form of matter rather than a force x distance concept of potential energy? The pairing of a proton and a neutron is a very stable configuration from an energy perspective.

This is not correct. A hydrogen atom (which has NO neutron) is a lot more stable than any of its isotopes. Thus, the pairing of a proton and a neutron does NOT produce a "very stable" configuration. The stability of a nuclear configuration is a lot more complex than that.

Or perhaps hockey players grabbing a puck ... but I appreciate your analogy. As I understand your analogy, the skaters would only get closer together if the other was still holding onto the ball. Otherwise, if it is just the momentum of the ball that moves the 'grabber' toward the 'grabbee', the two don't get very close - not unless the ball is much more massive than the player. So that begs the question: what is the skater/quark holding onto the ball/gluon with? Would you not have to assume some additional 'sticky' force there between the ball/gluon and the skater/quark?

The problem here is that there is a lack of understanding of quantum field theory. Keep in mind that QFT has been successfully used to obtain an accurate description of the band structure of the semiconductors that you are using in your modern electronics. So the validity of its methodology is well-known, even when you do not realize you are using it. The materials that you are using are littered with descriptions involving virtual phonons, magnons, spinons, polarons, etc.

So the fundamental issue now is to clearly understand QFT. Unfortunately, I think it is impossible to teach QFT online! :)

Zz.

 

[Andrew Mason]

This is not correct. A hydrogen atom (which has NO neutron) is a lot more stable than any of its isotopes. Thus, the pairing of a proton and a neutron does NOT produce a "very stable" configuration. The stability of a nuclear configuration is a lot more complex than that.

So is this incorrect?: http://hyperphysics.phy-astr.gsu.edu/hbase/particles/deuteron.html

The problem here is that there is a lack of understanding of quantum field theory. Keep in mind that QFT has been successfully used to obtain an accurate description of the band structure of the semiconductors that you are using in your modern electronics. So the validity of its methodology is well-known, even when you do not realize you are using it. The materials that you are using are littered with descriptions involving virtual phonons, magnons, spinons, polarons, etc.

So the fundamental issue now is to clearly understand QFT. Unfortunately, I think it is impossible to teach QFT online! :)

Next on my reading list is "An Introduction to Quantum Field Theory"

Andrew Mason

 

[quantumdude]

Could the binding energy not simply be stored in the form of matter rather than a force x distance concept of potential energy? The pairing of a proton and a neutron is a very stable configuration from an energy perspective. But when enough energy is added so that the particles are lifted out of that deep energy well, the result is a conversion of some of that matter back into energy.

Did you not see that the binding energy due to gravitation differs from the observed binding energy by about 38 orders of magnitude? Can you not perform a calculation to determine how much mass you would need to make up the difference? Just try it, and you'll see that it doesn't work.

Do we really have to be wedded to a concept of a 'force' within the nucleus? I say this knowing full well that there is probably something quite basic that I am missing so please be gentle on me.

I didn't say anything about forces. I spoke of binding energy.

Or perhaps hockey players grabbing a puck ... but I appreciate your analogy. As I understand your analogy, the skaters would only get closer together if the other was still holding onto the ball.

Nope. That's why I put them on ice skates. Even if the ball was dropped and rolled away, the skaters would move together, once the exchange had taken place.

Otherwise, if it is just the momentum of the ball that moves the 'grabber' toward the 'grabbee', the two don't get very close - not unless the ball is much more massive than the player.

Nope again. Look at the law of conservation of momentum. If the exchange is violent enough, the momentum transfer can be as high as you like.

So that begs the question: what is the skater/quark holding onto the ball/gluon with? Would you not have to assume some additional 'sticky' force there between the ball/gluon and the skater/quark?

The particles aren't holding onto the quanta with anything. Charged objects are sources of quanta. But as a side note, it is true in the case of the strong force that the quanta are also charged. But that is not necessary for the quanta to mediate the interaction, as demonstrated in the EM case.

 

[ZapperZ]

So is this incorrect?: http://hyperphysics.phy-astr.gsu.edu/hbase/particles/deuteron.html

You need to read what I said more carefully. I said

"This is not correct. A hydrogen atom (which has NO neutron) is a lot more stable than any of its isotopes."

"A lot more stable" does not mean one is stable and the other isn't. The fact that you can find more "H" or "H2" rather than "D" or "D2" imlies that H is more favorable to be formed than D.

So you are learning QFT? Have you also studied Second Quantization, which is practically the language of QFT?

Zz.

 

[Andrew Mason]

You need to read what I said more carefully. I said
"This is not correct. A hydrogen atom (which has NO neutron) is a lot more stable than any of its isotopes."

And I had said that a proton neutron pair is very stable. That is what I understood you to say was incorrect. I never said it was more stable than a proton. Probably nothing in the universe is as stable as a proton.

"A lot more stable" does not mean one is stable and the other isn't. The fact that you can find more "H" or "H2" rather than "D" or "D2" imlies that H is more favorable to be formed than D.

Or it simply implies that the D nucleus decays more rapidly than $^1_1H$. Perhaps we started with only neutrons in the universe and that resulted in more $^2_1H$ than $^1_1H$.

So you are learning QFT? Have you also studied Second Quantization, which is practically the language of QFT?

Not yet. I am brushing up on my undergraduate quantum physics text first and then we'll see how far I get. Thanks for the encouragement.

Andrew Mason

 

[Orion1]

Grainy Gravitation...

Did you not see that the binding energy due to gravitation differs from the observed binding energy by about 38 orders of magnitude? Can you not perform a calculation to determine how much mass you would need to make up the difference? Just try it, and you'll see that it doesn't work.

$$\propto_g = \frac{Gm_p^2}{\hbar c}$$

$$m_p$$ - proton mass

$$\propto_g = 5.904*10^{-39}$$

Andrew, how much mass is required to increase the gravitational fine structure constant to 1 ($$\propto_g = 1$$)?

Probably nothing in the universe is as stable as a proton.

Some GUT theories predict the proton as 'unstable'.

Actually, the electron is the most 'stable' particle known, however this is tangential because electrons cannot carry colour.

Andrew, I recommend studying Quantum Electrodynamics prior to Quantum Field Theory.

 

[ZapperZ]

Or it simply implies that the D nucleus decays more rapidly than $^1_1H$. Perhaps we started with only neutrons in the universe and that resulted in more $^2_1H$ than $^1_1H$.

And if you know this already, then this ring a bell that CLEARLY should have told you that a proton-neutron set up isn't as stable as a proton. Please note that originally, you are indicated that this set up is stable, as if it is the preferred ground state of a nuclei. I merely point out that it isn't when compared to a just a single proton as in the H atom. This means that the rest of your guesswork on the nucleon model falls apart. The nucleon structure isn't as naive as this. THAT is what I am trying to convey.

Zz.

 

[Andrew Mason]

Did you not see that the binding energy due to gravitation differs from the observed binding energy by about 38 orders of magnitude? Can you not perform a calculation to determine how much mass you would need to make up the difference? Just try it, and you'll see that it doesn't work.

There is no question that the observed binding energies in the nucleus are dozens of orders of magnitude greater than the gravitational binding energy of nuclear particles calculated using classical gravitational laws.

I didn't say anything about forces. I spoke of binding energy.

That's good. I am reluctant to equate the two concepts when speaking about the nucleus. I would like to leave open the possibility that the nuclear force might be viewed as something else - perhaps some kind of inertia in the process by which mass can be 'unraveled' into energy.

Nope. That's why I put them on ice skates.

Hockey players wear skates.

Even if the ball was dropped and rolled away, the skaters would move together, once the exchange had taken place.

I don't follow that. The momentum imparted by a particle is always in the direction of its motion. If the ball was pulled from the other skater and thrown back over the 'grabber's' head, they would move together because the grabbing skater would gain momentum in an equal and opposite direction to the ball. But the ball would depart the scene so it can't be repeated.

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. The problem, however, is that the 'pull' from each grab is greatest the farther apart they are (so long as the grabber is within 'arms length' of the ball) and gets smaller the closer they get.

Nope again. Look at the law of conservation of momentum. If the exchange is violent enough, the momentum transfer can be as high as you like.

But that momentum lasts only until the ball stops with the grabber. The faster the exchange, the shorter the grabber's motion lasts. Bottom line is that the centre of mass of the grabber and ball cannot change on each grab.

The particles aren't holding onto the quanta with anything. Charged objects are sources of quanta. But as a side note, it is true in the case of the strong force that the quanta are also charged. But that is not necessary for the quanta to mediate the interaction, as demonstrated in the EM case.

I can conceive of virtual particles being exchanged between quarks within a nucleus a lot easier than I can conceive of virtual photons being exchanged over huge distances in an electric/magnetic field. Is it just my lack of imagination? How is it that the force varies as $1/r^2$?

Andrew Mason

 

[Andrew Mason]

And if you know this already, then this ring a bell that CLEARLY should have told you that a proton-neutron set up isn't as stable as a proton. Please note that originally, you are indicated that this set up is stable, as if it is the preferred ground state of a nuclei.

That was not what I said nor what I was suggesting. I was using the pairing of a neutron and proton because, while it has a significant binding energy (which makes the configuration endure for long periods of time - hence stable), when it degenerates into separate particles there is a loss of mass. I was suggesting that we might think of the high binding energy of a neutron/proton pair as a 'resistance' to the 'unravelling' of matter rather than as a 'force' times 'distance'.

Andrew Mason

 

[quantumdude]

There is no question that the observed binding energies in the nucleus are dozens of orders of magnitude greater than the gravitational binding energy of nuclear particles calculated using classical gravitational laws.

OK, then what is it that prompts you to ask whether gravity can be responsible for nuclear binding? Clearly, nuclear stability cannot be accounted for by gravity as we know it. So you must be thinking of gravity as we don't know it.

Where does this idea come from?

How is it necessitated by any observational evidence?

Andrew: Or perhaps hockey players grabbing a puck ... but I appreciate your analogy. As I understand your analogy, the skaters would only get closer together if the other was still holding onto the ball.

Tom: Nope. That's why I put them on ice skates.

Andrew: Hockey players wear skates.

My remark was directed at the blue part.

Because the "particles" are on ice skates, they continue their motion, even if the ball is dropped after the exchange.

Tom: Even if the ball was dropped and rolled away, the skaters would move together, once the exchange had taken place.

Andrew: I don't follow that. The momentum imparted by a particle is always in the direction of its motion. If the ball was pulled from the other skater and thrown back over the 'grabber's' head, they would move together because the grabbing skater would gain momentum in an equal and opposite direction to the ball. But the ball would depart the scene so it can't be repeated.

But they are on ice skates, so the momentum that was imparted by the exchange does not change, even if no subsequent exchanges take place. And I didn't say anything about throwing the ball after the exchange, I said that even if the ball was dropped, the two would still be attracted. Of course, the exchange cannot be repeated as you note, but that is beside the point. You said that the two skaters would not move towards each other unless one skater was holding the ball, and that is incorrect.

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. The problem, however, is that the 'pull' from each grab is greatest the farther apart they are (so long as the grabber is within 'arms length' of the ball) and gets smaller the closer they get.

But that momentum lasts only until the ball stops with the grabber. The faster the exchange, the shorter the grabber's motion lasts. Bottom line is that the centre of mass of the grabber and ball cannot change on each grab.

No. The exchange only has to happen once, and the attraction would persist.

Once again, with emphasis: That's why I put them on ice skates.

The two skaters do not stop dead in their tracks once the ball is no longer being exchanged.

I can conceive of virtual particles being exchanged between quarks within a nucleus a lot easier than I can conceive of virtual photons being exchanged over huge distances in an electric/magnetic field. Is it just my lack of imagination?

Yes.

How is it that the force varies as $1/r^2$?

The inverse square law is derivable from QFT. In Zee's book, QFT in a Nutshell, he derives it in the first chapter.

However, you need to seek out some education in physics at the basic level first. You said that your next stop is Intro to QFT. That's an admirable sentiment, but you are just not ready for it. That much is apparent from the way you are struggling with the momentum issue with the ice skaters. You should revisit classical mechanics first, and then classical EM theory, then quantum mechanics.

And then try QFT on for size.

 

[marlon]

Andrew,

I suggest you follow the advice of Tom on the QFT-thing here, otherwise it is going to be very hard and even quasi impossible for you to grasp the basic notions of QFT. You not only need to understand the algorithms and "calculus" used in QFT, you also need to see how and why QFT and the fields in particular are introduced. There is a very profound history and reason for this and not knowing this is like studying General Relativity without knowing the concepts of Newtonian physics. It just won't work.

QFT is very hard to learn, yet it is the most interesting and useful model of physics that we have up till now. In my opinion even the LQG and String-theories are Spielerei (this means : "toys") compared to the "maturity" that QFT has reached. Learning this too fast will have the risk of dropping out very soon because you just won't get the point...

just some advice, don't take this the wrong way...
marlon

 

[Andrew Mason]

OK, then what is it that prompts you to ask whether gravity can be responsible for nuclear binding? Clearly, nuclear stability cannot be accounted for by gravity as we know it. So you must be thinking of gravity as we don't know it.
Where does this idea come from?

I am not saying that gravity accounts for nuclear stability. 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.

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).

How is it necessitated by any observational evidence?

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.

My remark was directed at the blue part.

I knew that. I was being facetious. I also play hockey.

Because the "particles" are on ice skates, they continue their motion, even if the ball is dropped after the exchange.

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

But they are on ice skates, so the momentum that was imparted by the exchange does not change, even if no subsequent exchanges take place.

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? 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.

And I didn't say anything about throwing the ball after the exchange, I said that even if the ball was dropped, the two would still be attracted. Of course, the exchange cannot be repeated as you note, but that is beside the point. You said that the two skaters would not move towards each other unless one skater was holding the ball, and that is incorrect.

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.

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"

No. The exchange only has to happen once, and the attraction would persist.

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})

Once again, with emphasis: That's why I put them on ice skates.

The two skaters do not stop dead in their tracks once the ball is no longer being exchanged.

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.

If one skater grabs the ball and brings it toward him and the ball stops, that skater must stop. If the other skater then grabs that ball and brings it to a stop against his chest, that skater moves a small distance toward the other and then stops.

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).

However, you need to seek out some education in physics at the basic level first. You said that your next stop is Intro to QFT. That's an admirable sentiment, but you are just not ready for it. That much is apparent from the way you are struggling with the momentum issue with the ice skaters.

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 should revisit classical mechanics first, and then classical EM theory, then quantum mechanics.

And then try QFT on for size.

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.

Andrew Mason

 

[Andrew Mason]

just some advice, don't take this the wrong way...
marlon

I do appreciate the advice. I know that the contributors to this board have the best of intentions and I am very grateful for the opportunity to discuss these things. It has spurred my interest in revisiting the difficult areas of physics that 30 years ago drove me into law. Law makes a wonderful career, mind you, but it isn't physics.

Andrew Mason

 

[humanino]

I am not saying that gravity accounts for nuclear stability. 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.

The question is whether observational evidence can have an alternate explanation.

The answer seems no, because the strong interaction applications are so numerous, and all in agreement with a very very simple, minimal assumption. Any other explanation would be more complicated. Occam razor.

I don't like the strong nuclear force.

I have contempt for lawyers. But I have no idea what being a lawyer could be so I am polite enough not to tell them, especially when I need their help.

we are just misunderstanding each other's posts here.

I doubt that we misunderstand yours.

 

[humanino]

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

This skater analogy has limits, it can not work so well at those scales, and will eventually run into difficulties. It was merely : the exchange can lead to either attraction or repulsion. But digging into it, I am not certain you will gain understanding in the nuclear interaction.

In my opinion, one should accept at some point, the historical developpement : if you are dealing with the proton/neutron structure, the first step is to understand the models which are not derived from fundamental laws. They are "intuited" with
1 classical analogies (as the skater, just closer to the problem)
2 quantum constraints
The reason one has to study those model : they work very well, for an approximative description. At the beginning, we had only innaccurate data, and those models were sufficient. And then, if you want to rigourously derive them, it is impossible. In order to gain understanding in the nuclei, you need to understand the meaning and the values of the parameters of the models.

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? 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.

You are running in the difficulties. This is not a ball exchanged. In fact, there are two parts : a scalar and a vector part. Those are intrisically mixed. They lead to a subtle balance between repuslion and attraction.

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.

See : this is mean. You know you are playing with an analogy. Do you only want to hear ? : at some point, any analogy fails. It only allows to communicate without equations, in order to emphasize a property. You extract the substance of a calculus, and then you think of an analogous phenomena, and you say "ok, remind in this simple case, it is the same ! " But you go "yes but also, if the ball is not inflated enough ... :tongue2: " This is not serious this skater thing. You are going nowhere with that.

Chiral Symmetry: Pion-Nucleon Interactions in Constituent Quark Models
http://smithers.physnet2.uni-hamburg.de/NN/NNnonlin.html

 

[Andrew Mason]

This skater analogy has limits, it can not work so well at those scales, and will eventually run into difficulties. It was merely : the exchange can lead to either attraction or repulsion. But digging into it, I am not certain you will gain understanding in the nuclear interaction.

I will go further than that and say that I am certain I won't.

See : this is mean. You know you are playing with an analogy. Do you only want to hear ? : at some point, any analogy fails. It only allows to communicate without equations, in order to emphasize a property. You extract the substance of a calculus, and then you think of an analogous phenomena, and you say "ok, remind in this simple case, it is the same ! " But you go "yes but also, if the ball is not inflated enough ... :tongue2: " This is not serious this skater thing. You are going nowhere with that.

I certainly did not intend to be mean and I apologize if it sounded like I was. But the analogy was yours. Conservation of momentum is not a minor detail. In order to have an exchange of gluons creating an enormous attractive force through momentum transfer, one would require some kind of imaginary negative momentum. I am not the only one who has had problems with the concept.

But don't give up on me just yet. I may surprise you with what I really do understand.

Andrew Mason

 

[Orion1]

Yukawa Aqua...

The lightest meson is the pion (quark anti-quark combination) which is NOT an elementary particle yet it DOES mediate a "part" of the strong force. I am referring to the socalled residual strong force that holds atomic nuclei together...

Can Deuterium Binding Energy be described as existing inside a Yukawa Potential Well?

Deuterium Binding Energy:
$$E_b = ((m_p + m_n) - m_D) E_n$$

Yukawa Potential Well:
$$U_y = f^2 \frac{e^{-\frac{r_D}{r_0}}}{r_D}$$

$$E_b = U_y$$

$$((m_p + m_n) - m_D) E_n = f^2 \frac{e^{- \frac{r_D}{r_0}}}{r_D}$$

$$f_D^2 = ((m_p + m_n) - m_D) E_n r_D e^{\frac{r_D}{r_0}}$$

$$\boxed{f_D = \sqrt{((m_p + m_n) - m_D) E_n r_D e^{\frac{r_D}{r_0}}}}$$

Key:
$$E_n = 931.5 \; Mev*amu^{-1}$$ - mass-energy equivalence
$$m_p$$ - Proton mass
$$m_n$$ - Neutron mass
$$m_D$$ - Deuterium mass
$$r_D$$ - Deuterium nuclear radius
$$r_0$$ - Yukawa nuclear range

 

[humanino]

But don't give up on me just yet. I may surprise you with what I really do understand.

I trust you Andrew, you must certainly understand very well parts of physics apart from nuclear theory.

Conservation of momentum is not a minor detail. In order to have an exchange of gluons creating an enormous attractive force through momentum transfer, one would require some kind of imaginary negative momentum. I am not the only one who has had problems with the concept.

This is a very good question indeed, and I have not been able to figure out a satisfactory answer yet. I will work on it, and probably benefit much from the other posts here.

But your argument is not only meant against QCD : two opposite electric charges attract by exchanging photons.

 

[Andrew Mason]

The answer seems no, because the strong interaction applications are so numerous, and all in agreement with a very very simple, minimal assumption. Any other explanation would be more complicated. Occam razor.

I'll have to take your word for it at the moment because I really don't understand it in the depth required to have an informed opinion. At this stage I am simply asking questions.

But let me just say that Occam's Razor is a bit of a cop out. Occam's Razor just a generalization, not a principle of science. It does not apply, for example, to the machinery of the cell - the simplest explanation is hardly ever the way it really works. It doesn't apply to General Relativity compared to Newton. Newton was an advocate of it as a principle but as subsequent developments have shown, things were not always as simple as he thought. It applies best in situations where there is more than one possible explanation and one has to determine the most probable one. If it walks like a horse, talks like a horse and smells like a horse then it is probably a horse, not a zebra - (unless, perhaps, you are in the African savannah).

I have contempt for lawyers. But I have no idea what being a lawyer could be so I am polite enough not to tell them, especially when I need their help.

Nelson Mandela is a lawyer. Mahatma Gandhi was a lawyer. Franklin D. Roosevelt and Abraham Lincoln were lawyers. You have contempt for them? Unfortunately, we are bound by our professional oath to defend people and causes that many people dislike. So we learn to develop a thick skin - a very useful thing to have in this forum, I have found.

Andrew Mason

 

[anti_crank]

I'll have to take your word for it at the moment because I really don't understand it in the depth required to have an informed opinion. At this stage I am simply asking questions.

You are welcome to ask questions. However, the other question is what to do with the answers you've gotten. This thread has many of the trademarks of the old TD forum; however, the scientific discussion has managed to stay above crackpot material for the time being.

We've given you plenty of reasons, complete with calculations, why gravity is irrelevant in the nucleus and why the strong force is needed. The strong force has been tested in many other ways. It successfully predicts meson structure and lifetimes. The existence of gluons has received huge support from three-jet events. On the theoretical side, the color quantum number is required for anomaly cancellation in the GWS model . Hence without colored quarks, the weak force theory would break down, and a large number of particle physics experiments would be open problems. The italicized terms are terms you might try to do Google searches on, since I don't have the time to explain those things.

Now you suggest that gravity and/or the EM force might behave differently on nuclear scales. Experimental evidence refutes this. For example, if Maxwell's equations were to break down at that scale, EM waves of wavelengths close to the size of nuclei (1fm) should behave differently than other EM waves. This corresponds to an energy of about 1.2 GeV, and experimental data is available that confirms QED to much greater energies (smaller scales).

As for gravity, this may sound like a catch-22 to you. We believe gravity is so weak on nuclear scales that its effects are impossible to measure. We attribute everything we observe to EM/strong/weak interactions. You might say we mistakenly attribute the new gravitational effects to the fictional strong force. But you must keep in mind that when accurate data is available, those models can be tested to great accuracy, and so far they passed every test. Therefore if you want to overthrow the strong force, it is not enough to make broad suggestions about gravity holding the nucleaus together. Rather, you must provide a mathematical description of gravity that reproduces all those effects, then proceed to solve the other problems that the absence of strong nuclear forces would create.

At this point, you might argue that you don't have the training, the knowledge or the skills to make such a model. In that case, and with all due respect, please leave the physics to the physicists. I like to think that no physicist would tell you how to do your job, and I ask for the same professional courtesy from you. We do not have contempt for lawyers; I suspect humanimo was simply offended by your statement that you "don't like" the strong force. More on that later.

But let me just say that Occam's Razor is a bit of a cop out. Occam's Razor just a generalization, not a principle of science. It does not apply, for example, to the machinery of the cell - the simplest explanation is hardly ever the way it really works. It doesn't apply to General Relativity compared to Newton. Newton was an advocate of it as a principle but as subsequent developments have shown, things were not always as simple as he thought.

This was a completely different matter. The theories made different predictions, and experiments falsified Newton and supported Einstein.

It applies best in situations where there is more than one possible explanation and one has to determine the most probable one.

Is that not exactly what we would have here? Assuming that you somehow manage to construct a model of gravity/EM that does what you want, it will undoubtedly be very complicated. Why should that be the most probable then? The current theories, with the strong force included, are simpler than anything thus constructed. Of all the branches of science, particle physics is especially driven towards greater simplicity, and this drive is what makes for most of today's effort in this field.

In case you haven't noticed, I don't like the strong nuclear force.

This is an extremely unscientific attitude. We expect this from creationists who don't like the vast majorities of present theories, classical-physics mindsets who feel their worlds coming apart at the mere thought of relativity or quantum mechanics, and other crackpots who are fixated on one idea and cannot let go of it. In science, personal opinions are a luxury. Furthermore, personal opinions without some valid scientific or mathematical backing are not even science. This is not a good path you're heading down; consider this an attempt to pull you away from the edge.

 

[Andrew Mason]

Now you suggest that gravity and/or the EM force might behave differently on nuclear scales. Experimental evidence refutes this. For example, if Maxwell's equations were to break down at that scale, EM waves of wavelengths close to the size of nuclei (1fm) should behave differently than other EM waves. This corresponds to an energy of about 1.2 GeV, and experimental data is available that confirms QED to much greater energies (smaller scales).

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.

As for gravity, this may sound like a catch-22 to you. We believe gravity is so weak on nuclear scales that its effects are impossible to measure. We attribute everything we observe to EM/strong/weak interactions. You might say we mistakenly attribute the new gravitational effects to the fictional strong force.

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.

At this point, you might argue that you don't have the training, the knowledge or the skills to make such a model. In that case, and with all due respect, please leave the physics to the physicists. I like to think that no physicist would tell you how to do your job, and I ask for the same professional courtesy from you.

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.

The current theories, with the strong force included, are simpler than anything thus constructed. Of all the branches of science, particle physics is especially driven towards greater simplicity, and this drive is what makes for most of today's effort in this field.

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. Biology explains macroscopic life forms in terms of more fundamental units of life: the cell. Molecular biology seeks to explain complex behaviour of cells in terms of fundamental processes (protein synthesis being governed by the machinery of RNA/DNA transcription and translation). Physical chemistry explains the composition of matter in terms of combinations of a finite number of kinds of atoms and the electromagnetic forces between atoms. Physics explains all atoms as combinations of nucleons and electrons.

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.

This is an extremely unscientific attitude. We expect this from creationists who don't like the vast majorities of present theories, classical-physics mindsets who feel their worlds coming apart at the mere thought of relativity or quantum mechanics, and other crackpots who are fixated on one idea and cannot let go of it. In science, personal opinions are a luxury. Furthermore, personal opinions without some valid scientific or mathematical backing are not even science.

I do agree with you there. I never said the fact that I didn't 'like' an explanation was a reason to reject the explanation. I just meant it was reason for me to keep trying to see if there is not another more fundamental explanation that fits the evidence.

Andrew Mason