Why Gravity is Significant in Proton & Neutron Nuclei

[Andrew Mason]

Can anyone explain to me why gravity would not be a significant force on the 'surface' of a proton or neutron? A quick calculation shows that the acceleration of a neutron toward another neutron or a proton separated by less than the radius of a neutron, is very large (compared to the radius of the neutron). The acceleration is several orders of magnitude greater than the radius of the neutron / sec^{2}:

G = 6.67 \times 10^{-11} Nm^2 /kg^{2}

1) diameter of nucleus of H is ~ 10^{-15} m
radius of nucleus is: 5 \times 10^{-16} m

2) mass nucleus of H is 1.66 \times 10^{-27} kg.

3) gravitational force and acceleration between two protons in He nucleus is:

F = GmM/r^2

F = 6.67 \times 10^{-11} \times (1.66 \times 10^{-27})^2 \div (5 \times 10^{-16})^2

F = .735 \times 10^{(-65+32)}

F = 7.35 \times 10^{-34} N

F = m a

a = F / m

a = 7.35 \times 10^{-34} \div 1.66 \times 10^{-27}

a = 4.43 \times 10^{-7} m/sec^2

Since the radius of the proton is ~ 10^{-15} m, this seems like a significant acceleration, or am I missing something?

Andrew Mason

 

[mathman]

I won't claim any expertise here, but I understand at the level (subatomic particles) being considered, things don't act like solid balls. Quantum theory rules here.

 

[Nereid]

Try doing a similar calculation Andrew, for the acceleration between two protons in a nucleus (make similar, classical, assumptions) ... let us know what you find!

 

[Andrew Mason]

Try doing a similar calculation Andrew, for the acceleration between two protons in a nucleus (make similar, classical, assumptions) ... let us know what you find!

Since the mass of the proton and neutron are the same, the gravitational force is the same. Of course we ignore how we get two protons together and overcome the repulsive electrical forces.

Andrew Mason

 

[humanino]

Of course... That might be what Nereid meant !

Beside, you cannot only compare an acceleration to a distance, at first it does not make sens. You need either to know either a speed, or a time scale. Gravity must come out negligible in any case. Besides, the strong interaction is named because it is even larger than the EM interaction.

 

[Nereid]

Since the mass of the proton and neutron are the same, the gravitational force is the same. Of course we ignore how we get two protons together and overcome the repulsive electrical forces.

Andrew Mason

Indeed; my point was to compare the numbers for gravitation and EM, using the same calculations: "A quick calculation shows that the acceleration of a [proton] [away from] another [proton] separated by less than the radius of a [proton], is very large (compared to the radius of the [proton])." Within this very restrictive (and unrealistic) set of assumptions, by how many OOM (orders of magnitude) is the EM acceleration greater than the gravitational one?

(Once you've given us the calculations Andrew, you might like to provide an operational definition of 'negligible' )

 

[arivero]

Hmm one should compare forces to forces, potatoes to potatoes. So nuclear (pions) fermi force is the one to check here.

 

[humanino]

I think the easiest way to do so, is to compare potential energies.

 

[Andrew Mason]

Of course... That might be what Nereid meant !

Beside, you cannot only compare an acceleration to a distance, at first it does not make sens.

What is important, it seems to me, is the time required for significant changes in separation to occur. When you are contemplating protons and neutrons in the nucleus, the separation distances are very small. While the Earth produces much greater gravitational acceleration at its surface than a proton does at its surface, the time required for signficant changes in separation to be reduced by gravity is much greater:

Example:
For an object that is .01 Earth radius above the Earth (about 60 km), the time required to return to the surface (ignoring friction) is:

t = \sqrt{2s/g}

g \approx 10 m/sec^2

t = \sqrt{2 \times 120 \times 10^3/10} = 154 seconds

For a proton separated from a neutron by .01 radius of a neutron, the time required to return to the surface of the neutron is:


\therefore t = \sqrt{5 \times 10^{-18}/4 \times 10^{-7}} = 3.5 \times 10^{-5} sec.

(s = .01 \times radius of neutron = 5 \times 10^{-18}m.)

(a \approx 4 \times 10^{-7} m / sec^2)

You need either to know either a speed, or a time scale. Gravity must come out negligible in any case. Besides, the strong interaction is named because it is even larger than the EM interaction.

If we are interested in identifying what keeps the nucleus together (as opposed to what keeps a proton together) the essential question is: what are the forces that work against it?

The magnitude of gravity within the nucleus may be small by comparison to the EM interaction, but how do we know that the EM interaction applies within the nucleus? If it does, then obviously gravity would not be sufficient to keep the nucleus together. But I am not sure that it does. I was hoping someone out there might be able to explain why gravity is not sufficient.

Andrew Mason

 

[humanino]

No, gravity by itself is far not sufficient to overcome EM repulsion. It is only the residual strong interaction potential which keeps the nucleons together. Have you calculated EM repulsion ?

 

[Andrew Mason]

No, gravity by itself is far not sufficient to overcome EM repulsion. It is only the residual strong interaction potential which keeps the nucleons together. Have you calculated EM repulsion ?

I never said gravity by itself was sufficient to overcome EM repulsion. It is dozens of orders of magnitude smaller. But I am not assuming that it has to overcome EM repulsion in order for the nucleus to stay together (ie. once it is together).

If you put H nuclei together create He, one has to use a lot of energy to overcome the EM repulsion (ie. it requires the energy inside a star). But once fusion occurs, do we know that the EM repulsion continues to operate between protons in the nucleus? That would be my question.

EM repulsion certainly doesn't continue when two protons fuse to produce deuterium (and emit a positron). Does EM repulsion continue when an extra proton is added to the nucleus?

Andrew Mason

 

[zefram_c]

Of course EM repulsion continues within the nucleus. That is why heavier nuclei with a lot of protons are unstable - the repulsion is stronger than the nuclear attractive forces. That's also why no elements with more than 100 protons exist in nature - they're very unstable.

 

[Andrew Mason]

Of course EM repulsion continues within the nucleus. That is why heavier nuclei with a lot of protons are unstable - the repulsion is stronger than the nuclear attractive forces. That's also why no elements with more than 100 protons exist in nature - they're very unstable.

That doesn't necessarily mean that EM repulsion continues within the nucleus of He. It may be that EM forces have a minimum range: they do not apply within a region of space that is larger than a He nucleus but smaller than a nucleus of Einsteinium.

I am not saying this is actually the case. I am wondering if anyone can explain why it is not the case.

Andrew Mason

 

[Nereid]

I think you've heard of scattering experiments Andrew, in which a beam of electrons (or protons) hits a target of protons (H nuclei); if you read up on those, I think you'll find that there's very clear experimental data to show that the EM force doesn't weaken at short distances; at least to the experimental limit.

 

[Andrew Mason]

I think you've heard of scattering experiments Andrew, in which a beam of electrons (or protons) hits a target of protons (H nuclei); if you read up on those, I think you'll find that there's very clear experimental data to show that the EM force doesn't weaken at short distances; at least to the experimental limit.

Scattering experiments are, for the most part, done with electrons, not protons. The result is that we do not measure electrical repulsion between protons. Perhaps you can explain to me how electron scattering shows that EM force exists within the nucleus and, in particular, that proton-proton repulsion exists within the nucleus.

If electron-proton EM attraction exists to within a very small distance from the nucleus, why is there not some electron energy at which the electron reaches the nucleus but cannot escape it - ie it joins the nucleus? The quantum mechanical explanation of the electrons in the atom based on the uncertainty principle may be quite correct but begs the question: does EM force really have any meaning when elementary charged particles get very close?

Andrew Mason

 

[ZapperZ]

If electron-proton EM attraction exists to within a very small distance from the nucleus, why is there not some electron energy at which the electron reaches the nucleus but cannot escape it - ie it joins the nucleus? The quantum mechanical explanation of the electrons in the atom based on the uncertainty principle may be quite correct but begs the question: does EM force really have any meaning when elementary charged particles get very close?

Andrew Mason

Andrew,

When you look at the Schrodinger equation for the hydrogen atom, for example, what do you think that "V" term is?

Furthermore, you don't use the "uncertainty principle" to accurately solve for the energy states, etc. of an atom.

As for electron not reaching the nucleus, who said that? There is a difference between the BOUND STATE solution of an atom, where there is a minium, ground state for an electron-atom system, and free electron colliding with a bare proton/nucleus, which can induce an inverse beta decay! In the latter case, you CAN have an electron capture with the appropriate momentum conservation condition.

Zz.

 

[Nereid]

Scattering experiments are, for the most part, done with electrons, not protons. The result is that we do not measure electrical repulsion between protons. Perhaps you can explain to me how electron scattering shows that EM force exists within the nucleus and, in particular, that proton-proton repulsion exists within the nucleus.

If electron-proton EM attraction exists to within a very small distance from the nucleus, why is there not some electron energy at which the electron reaches the nucleus but cannot escape it - ie it joins the nucleus? The quantum mechanical explanation of the electrons in the atom based on the uncertainty principle may be quite correct but begs the question: does EM force really have any meaning when elementary charged particles get very close?

Andrew Mason

You might like to google on 'proton-proton scattering'; it would seem that there have been quite a few such experiments, over a wide range of energies.

I'll leave it to a PF member more familiar with this work than I am to say something about the results of scattering experiments wrt your idea that the EM force may have a different behaviour either in nuclei or over short ranges (or both).

 

[humanino]

We use quantum electrodynamics to probe the proton structure at very small distance. For instance at 6 GeV, we are under 2\times10^{-17}m.
If course if you insist in saying "what about thousand times smaller than any actual accessible distance" we would have to give up.

 

[Andrew Mason]

Andrew,
When you look at the Schrodinger equation for the hydrogen atom, for example, what do you think that "V" term is?

The Schrodinger equation provides an accurate mathematical model for the quantum mechanical behaviour of the atom, in which EM potential is obviously important. Inside the nucleus may be another matter.

Furthermore, you don't use the "uncertainty principle" to accurately solve for the energy states, etc. of an atom.

I agree. But one does use it to explain why the electron doesn't simply 'fall' into the nucleus due to EM attraction.

As for electron not reaching the nucleus, who said that? There is a difference between the BOUND STATE solution of an atom, where there is a minium, ground state for an electron-atom system, and free electron colliding with a bare proton/nucleus, which can induce an inverse beta decay! In the latter case, you CAN have an electron capture with the appropriate momentum conservation condition.

But it is quite rare and it is not stable. One might think (classically) that the EM attraction would bring it into the nucleus and keep it there, if EM attraction was that strong inside the nucleus.

It is assumed that strong nuclear attractive force works against the coulomb repulsion force that exists between protons. This means that the nuclear force is strong only in the region very close to the nucleus. I am looking for the evidence that this is in fact the case. I am suggesting that the same result would occur if the coulomb force had a minimum range (ie did not operate inside a certain the region close to the proton) so that the force which keeps protons together is something much weaker. I am suggesting, if that is the case, that gravity might actually be the dominant force inside the nucleus.

Andrew Mason

 

[ZapperZ]

It is assumed that strong nuclear attractive force works against the coulomb repulsion force that exists between protons. This means that the nuclear force is strong only in the region very close to the nucleus. I am looking for the evidence that this is in fact the case.

I'm sorry, but is this still in doubt? A nucleus consists of a bunch of positively charged protons, and neutral neutrons. If there's nothing else that not only counter the coulombic repulsion, but also is way stronger than the coulombic repulsion, don't you think the nucleus would fly apart?

I am suggesting that the same result would occur if the coulomb force had a minimum range (ie did not operate inside a certain the region close to the proton) so that the force which keeps protons together is something much weaker. I am suggesting, if that is the case, that gravity might actually be the dominant force inside the nucleus.

Andrew Mason

You can suggest anything you like, but without (i) a self-consistent theory and/or (ii) experimental impetus to suggest that, then you might as well propose that bored angels in their spare time pushes the nucleons together. To allow for what you are proposing, you have to rewrite the whole of Maxwell Equations, since the 1/r potential obviously have to be corrected.

What I'm puzzled with is that there ALREADY is a verified, consistent explanation/description for the strong force. What is WRONG with it that is causing you to come up with a whole new speculation on why nucleons can stick together in spite of the coulombic force? Did you find a flaw in the Glashow/Salam/Weinberg model that is causing you to refute their theory? Are you proposing that QCD be dumped in favor of your "gravity"?

Zz.

 

[marlon]

Andrew,

I suggest you need to look at the socalled "BETA-FUNCTION" of the strong-force-coupling constant AND the fact it is negative. You know : the famous asymptotic freedom...

As you will know it makes sure that a proton (just like any other baryon) is built out of three quarks with a different colour each so the colour-neutrality is always respected. The EM-processes are much much weaker when looked at some nucleus at quark-scale and this biggest problem you would have is there is no short-range for EM. The mediators will never acquire mass through the Higgs-mechanism.

QCD predicts that the interquark-potential is linear in the long range. So this basically means that in the vacuum state, the quarks will tend to form doublets or triplets...ie mesons and baryons.

I don't really see your problem with a theory that is already well established (apart from the quark-confinement ofcourse) and experimentally verified...

Indeed, in the short range the strong force becomes repulsive, yet this effect is much smaller compared to the i) long range attractive part of the strong force and ii) the attractive residual strong force mediated by the pions...which have mass and thus describe a short range "attractive" interaction. Why attractive? Well, because of the omnipresent colour-neutrality. Just look at how pions are created via the screening-effect in QCD...


regards
marlin

 

[ZapperZ]

As you will know it makes sure that a proton (just like any other fermion) is built out of three quarks with a different colour each so the colour-neutrality is always respected.

Er.. I think you mean ".. like any other baryon...", not fermion, especially if you are giving a "three quark" content example.

Zz.

 

[marlon]

Er.. I think you mean ".. like any other baryon...", not fermion, especially if you are giving a "three quark" content example.

Zz.

Yes indeed, Zz. Thanks for the correction...my mistake...

marlon

 

[Andrew Mason]

You can suggest anything you like, but without (i) a self-consistent theory and/or (ii) experimental impetus to suggest that, then you might as well propose that bored angels in their spare time pushes the nucleons together. To allow for what you are proposing, you have to rewrite the whole of Maxwell Equations, since the 1/r potential obviously have to be corrected.

Well, at some point the 1/r potential breaks down because the proton is not a point charge - it has a finite size. You are not suggesting that the potential goes to - infinity inside the proton are you? I am just suggesting that it might break down in a region that is outside the proton 'surface'.

What I'm puzzled with is that there ALREADY is a verified, consistent explanation/description for the strong force. What is WRONG with it that is causing you to come up with a whole new speculation on why nucleons can stick together in spite of the coulombic force? Did you find a flaw in the Glashow/Salam/Weinberg model that is causing you to refute their theory? Are you proposing that QCD be dumped in favor of your "gravity"?

I am just questioning the existing theory is correct. I am asking what evidence we have that there is a strong nuclear force.

So far the explanation has been, 1. protons repel protons with enormous EM force (\propto 1/r^2) that continues down to the 'surface of the proton'; 2. the nucleus consists of protons having a separation less than the radius of a proton and the nucleus does not fly apart. 3. Therefore there must be a strong nuclear force that is much greater than the coulombic repulsion forces but which operates only in the region of the nucleus.

3 necessarily follows from 1 and 2. I am just asking what evidence we have that 1 is correct.

Andrew Mason

 

[humanino]

Well, at some point the 1/r potential breaks down because the proton is not a point charge - it has a finite size.

Even within classical mechanics, this does not imply failure of the EM. Right the 1/r potential of the proton fails, but why would it be so for the point-like constituants ? From far away the proton looks like a point, and when you get near, you can see it is a ball, and if you get near enough, you can actually see the sub-structure. Everything in accordance with EM, or its quantum version necessary to describe the scattering process. But still, it is EM.

 

[humanino]

1) is wrong
Please read [thread=41110]this thread[/thread] about nuclear interactions.

 

[ZapperZ]

Well, at some point the 1/r potential breaks down because the proton is not a point charge - it has a finite size. You are not suggesting that the potential goes to - infinity inside the proton are you? I am just suggesting that it might break down in a region that is outside the proton 'surface'.

But you just answered your own question. If it is NOT a point charge, then you'll never get to an infinite potential. So what's the problem?

I am just questioning the existing theory is correct. I am asking what evidence we have that there is a strong nuclear force.

Do you even KNOW what the "existing theory" is, i.e. have you studied QFT, QED, and QCD? Or is this questioning simply based on ignorance that you acquired via reading pop-science books?

So far the explanation has been, 1. protons repel protons with enormous EM force (\propto 1/r^2) that continues down to the 'surface of the proton'; 2. the nucleus consists of protons having a separation less than the radius of a proton and the nucleus does not fly apart. 3. Therefore there must be a strong nuclear force that is much greater than the coulombic repulsion forces but which operates only in the region of the nucleus.

3 necessarily follows from 1 and 2. I am just asking what evidence we have that 1 is correct.

Andrew Mason

The discovery of the quarks AND the verification of the hirerchy of the quark model ARE the evidence of the strong force! QCD includes ALL the strong interactions and decay channels that make predicitons on what and where to look in a particle collider.

Zz.

 

[Andrew Mason]

Even within classical mechanics, this does not imply failure of the EM. Right the 1/r potential of the proton fails, but why would it be so for the point-like constituants ? From far away the proton looks like a point, and when you get near, you can see it is a ball, and if you get near enough, you can actually see the sub-structure. Everything in accordance with EM, or its quantum version necessary to describe the scattering process. But still, it is EM.

I am not the first to suggest that classical EM theory breaks down at the atomic level (eg. Planck's solution to the ultra-violet catastrophe).

We know that the proton, as with all elementary particles, can be expressed as a wave function. This suggests that when we get down to the regions of the 'surface' of the proton, things get fuzzy.

Within that fuzzy region, we cannot assume that electro-magnetic forces follow classical laws. Since the entire nucleus appears to be within the 'fuzzy region' and since the 'evidence' of the strong force seems to be an inference based on the assumption that enormous EM repulsion exists within the nucleus, I am questioning whether the strong force is real.

So I just ask the question: what evidence do we have for the strong nuclear force that is independent of any assumption that strong EM repulsion forces operate between protons within the nucleus? I am not suggesting it doesn't exist. I am just not aware of it.

Andrew Mason

 

[Andrew Mason]

But you just answered your own question. If it is NOT a point charge, then you'll never get to an infinite potential. So what's the problem?

If the proton was a perfect sphere with positive charge distributed uniformly over the surface, the 1/r^2 force would apply only down to the surface (EM force would be 0 inside). But the proton is not a perfect sphere. It is a wave function that has rather fuzzy boundaries. It seems that the existence of the strong nuclear force is based on the assumption that EM repulsion continues to follow the 1/r^2 relationship to a point that appears to be within that fuzzy boundary.

Do you even KNOW what the "existing theory" is, i.e. have you studied QFT, QED, and QCD? Or is this questioning simply based on ignorance that you acquired via reading pop-science books?

I am just asking questions. All questions are based on ignorance. Otherwise, why ask the question?

I don't pretend to have more than a rudimentary grasp of quantum theory. I studied it as an undergraduate in physics but that was many years ago. And I ended up as a lawyer.

The discovery of the quarks AND the verification of the hirerchy of the quark model ARE the evidence of the strong force! QCD includes ALL the strong interactions and decay channels that make predicitons on what and where to look in a particle collider.

My question was: What evidence is there that protons repel protons with enormous EM force (\propto 1/r^2) that continues down to the 'surface of the proton'.

Andrew Mason

 

[humanino]

I am not the first to suggest that classical EM theory breaks down at the atomic level (eg. Planck's solution to the ultra-violet catastrophe).

How old is that ?

We know that the proton, as with all elementary particles, can be expressed as a wave function. This suggests that when we get down to the regions of the 'surface' of the proton, things get fuzzy.

It would be meaningless to describe the proton as a wave by itself. This wave is a tensor product of the waves of the constituants.

Within that fuzzy region, we cannot assume that electro-magnetic forces follow classical laws. Since the entire nucleus appears to be within the 'fuzzy region' and since the 'evidence' of the strong force seems to be an inference based on the assumption that enormous EM repulsion exists within the nucleus, I am questioning whether the strong force is real.

We will soon be able to provide a snapshot of the interior of the proton. Total information on the content, that is the Wigner pseudo-probability distribution in phase space. The strong force is real there is definitely no doubt.

So I just ask the question: what evidence do we have for the strong nuclear force that is independent of any assumption that strong EM repulsion forces operate between protons within the nucleus? I am not suggesting it doesn't exist. I am just not aware of it.

Classification of hundreds of particles : the hadrons. The zoo of strongly bound states is far from random. It obeys symmetry. Those symmetries are beautifully interpreted in the standard-model. Besides, there is no such thing as a "strong EM repulsion". It is weak as compared to the strong force.

 

[ZapperZ]

If the proton was a perfect sphere with positive charge distributed uniformly over the surface, the 1/r^2 force would apply only down to the surface (EM force would be 0 inside). But the proton is not a perfect sphere. It is a wave function that has rather fuzzy boundaries. It seems that the existence of the strong nuclear force is based on the assumption that EM repulsion continues to follow the 1/r^2 relationship to a point that appears to be within that fuzzy boundary.

But I can ask you the same thing: what evidence do you have that the valid EM laws simply break down at a certain scale? While EM laws that we have are known to work, your guess work hasn't. So the "burden of proof" (something YOU should know about) is in your court. It is up to you to show that there ARE evidence to suggest that your idea might be valid.

I am just asking questions. All questions are based on ignorance. Otherwise, why ask the question?

But you already stated that you ARE questioning the validity of QCD. Maybe I am simply a foolish person, but if I were to question the validity of something, I would want to make sure I have understood as much as I can about that thing. So these simply aren't just "questions" out of curiousity.

My question was: What evidence is there that protons repel protons with enormous EM force (\propto 1/r^2) that continues down to the 'surface of the proton'.

Andrew Mason

The validity of EM and QED. On the other hand, what evidence do YOU have that Maxwell equation and/or QED do not work down to the "surface of the proton"?

Zz.

 

[Andrew Mason]

But I can ask you the same thing: what evidence do you have that the valid EM laws simply break down at a certain scale? While EM laws that we have are known to work, your guess work hasn't.

But EM laws do break down at the atomic level, which is why we have quantum theory. So the question is not whether they break down. The question is: at what point are they no longer valid?

So the "burden of proof" (something YOU should know about) is in your court. It is up to you to show that there ARE evidence to suggest that your idea might be valid.

At this stage I am cross-examining the evidence. I don't have to come up with a valid theory at this stage to test the prosecution's case.

But you already stated that you ARE questioning the validity of QCD. Maybe I am simply a foolish person, but if I were to question the validity of something, I would want to make sure I have understood as much as I can about that thing. So these simply aren't just "questions" out of curiousity.

In an ideal world I would have read and understood textbooks on quantum theory, tensor analysis, and general relativity and know how to develop Schrodinger's equation from first principles. I don't live in an ideal world.

The validity of EM and QED. On the other hand, what evidence do YOU have that Maxwell equation and/or QED do not work down to the "surface of the proton"?

But IF <A=the existence of the strong nuclear force> is in some part based on the assumption that <B=the EM field equations apply down to the surface of the proton>, and IF <C=EM field equations are known to break down at some point at the atomic level> THEN the onus would be on the proponent of A to show B is true. I don't have to lead evidence for a verdict of 'not proven'.

Andrew Mason

 

[ZapperZ]

But EM laws do break down at the atomic level, which is why we have quantum theory. So the question is not whether they break down. The question is: at what point are they no longer valid?

Hello? I asked you earlier what that "V" is in the Schrodinger equation that is USED to find all those solutions to an atom. Where do you think this came from?! This is exactly the coulombic potential from E&M!

At this stage I am cross-examining the evidence. I don't have to come up with a valid theory at this stage to test the prosecution's case.

This assumes that you have the ability to understand the evidence. Presumably, if you are not an expert in the field, you bring in experts that can evaluate the evidence. The experts in the fields have spoken, in VOLUMES of work in peer-reviewed journals.

So now what?

But IF <A=the existence of the strong nuclear force> is in some part based on the assumption that <B=the EM field equations apply down to the surface of the proton>, and IF <C=EM field equations are known to break down at some point at the atomic level> THEN the onus would be on the proponent of A to show B is true. I don't have to lead evidence for a verdict of 'not proven'.

Andrew Mason

Read above on why your so-called evidence that EM fields break down at the atomic level isn't valid. Thus, there are no such instances in this case.

Zz.

 

[humanino]

But IF <A=the existence of the strong nuclear force> is in some part based on the assumption that <B=the EM field equations apply down to the surface of the proton>, and IF <C=EM field equations are known to break down at some point at the atomic level> THEN the onus would be on the proponent of A to show B is true. I don't have to lead evidence for a verdict of 'not proven'.

Andrew, seriously, let us be honest :
C) holds for sure. There is no doubt. I told you everybody uses everyday the standard model down to 10^{-16}m and even less ! We do not see any problem with it. We wish we could find a problem, some would kill to find a small clue for a problem !

B) Sure holds. Here at the lab we throw electrons on protons. No problem. We too apply the standard model more than one order of magnitude smaller than the size of the proton. We probe it down to a scale about one hundredth its size. Its working. I told you we will soon deliver a snapshot of the constituents, and you keep telling us "but you don't know what you're doing"

A) holds too. It explains so many things. We work nuclear plants with it, and satisfactory make calculations about the power of the Sun. We have a simple, symmetry-based model called QCD, from which we can actually prove the most successful model of the nuclear forces : the Skyrme force. You need not understand all the details. This model has been discovered after a long work, mainly based on both satisfying the quantum rules and using semi-classical approximations, and the model was proven to work great ! Only recently did we understand how the model was justified by the fundamental QCD. So now we understand how the forces (Skyrme) between protons and neutrons in the nucleus emerge as residual forces of the interaction between the constituents (QCD) which are quarks and glue. Those are facts. I am telling you, this is worth studying it, there is no reason to doubt about it. Every day in other lab they collide heavy ions, and check the laws in the regime where perturbative technics apply : it works. The instanton models are based on the fundamental QCD, they are able to predict the mass of maybe more than 80% of hadrons within less than 10% accuracy, and we know from the beginning that they are approximations. Really, I swear, it does not make sens to say the strong interaction is spurious ! We can't display in front of your eyes more than half a century of planetary efforts, involving hundreds of thousands of passionated people, all of them eager to find the least flaw anywhere.

Andrew, please, ask serious questions. There are so many informations everywhere. We told you why your first calculation is wrong : you do not even take into account EM. And you answer "but all of you guys are wrong with this" you throw this at our face. This is not fair. We are ready to help you understand what we are doing, but you can't tell us "the entire middle-age history is fake. I did not read it, but I know those little green men erased all they've been doing during thousand years, and replaced it with a fairy tale" What are we supposed to do ? Tell you the all middle-ages history and you point every little detail until you understood we were right ? This is insane ! I am unable to do it anyway ! You have to trust your peers at some point, and as long as nothing comes wrong with what has been said, you cannot redo all the experiments at home !

 

[Andrew Mason]

Andrew, seriously, let us be honest :
C) holds for sure. There is no doubt. I told you everybody uses everyday the standard model down to 10^{-16}m and even less ! We do not see any problem with it. We wish we could find a problem, some would kill to find a small clue for a problem !

I never said there was a problem with the experimental evidence. I am wondering whether there might be more than one explanation for some of it ie. something other than a force. I am trying to determine, without doing a post-graduate program in nuclear physics, what the evidence is for the existence of these strong nuclear forces.

B) Sure holds. Here at the lab we throw electrons on protons. No problem. We too apply the standard model more than one order of magnitude smaller than the size of the proton. We probe it down to a scale about one hundredth its size. Its working. I told you we will soon deliver a snapshot of the constituents, and you keep telling us "but you don't know what you're doing"

I never said that. I simply asked the questions: how do we know that there is a strong nuclear force? and how do we know that protons exert EM repulsive force within the nucleus?

I just thought there might be a simple answer to those questions.

So now we understand how the forces (Skyrme) between protons and neutrons in the nucleus emerge as residual forces of the interaction between the constituents (QCD) which are quarks and glue. Those are facts. I am telling you, this is worth studying it, there is no reason to doubt about it. ...

... Really, I swear, it does not make sense to say the strong interaction is spurious ! We can't display in front of your eyes more than half a century of planetary efforts, involving hundreds of thousands of passionated people, all of them eager to find the least flaw anywhere.

Andrew, please, ask serious questions.

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

 

[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.