Can magnetism exist independently of current or charge?

[MannyP2011]

Can magnetism exist independently of current or charge?
I'm just curious because the intertwining relationship between E&M.

 

[Vanadium 50]

No. If there were no electric charges, there would be no magnetic fields.

 

[MannyP2011]

I asked my professor( he has a PhD in Particle Physics) and he said magnetism can exist independently of charges but he didn't explain why during a E&M class.
I ask this because I wonder why the speculation of magnetic monopoles if magnetism is just an effect of moving charges and there are only certain ways that charges can move through space and obviously if all of the possibilities of motion must have to been exhausted since the nobel prize in the waiting if they where found.
Why do people still speculate about magnetic monopoles existing?

 

[kcdodd]

his remark probably comes from Maxwells equations, which has solutions when charge and current density is zero.

 

[Phrak]

I asked my professor( he has a PhD in Particle Physics) and he said magnetism can exist independently of charges but he didn't explain why during a E&M class.
I ask this because I wonder why the speculation of magnetic monopoles if magnetism is just an effect of moving charges and there are only certain ways that charges can move through space and obviously if all of the possibilities of motion must have to been exhausted since the nobel prize in the waiting if they where found.
Why do people still speculate about magnetic monopoles existing?

A perm. magnet can have a magnetic field without charge or current.Magnetic monopoles (or magnetic charge, really) bring a beautiful symmetry to Maxwell's equations that beg for expression. --the problem being, of course, that no one has seen any in vacuum.

Actually, I found a cheat--a classical way around it--at least in part. I'm bragging here, a little. Maxwell's equations can be formulated with complex electromagnetic potential in place of real valued potential.

A <-- A + iZ​

This would gives rise to magnetic charge. So how do we get ride of this seemingly nonphysical result? Global gauge fixing the complex phase would be sufficient.

A <-- Ae^iM is unmeasurable​

Local gauge fixing would allow magnetic charge at a distance, but at the same time, any necessarily local measurement of magnetic charge or current would return a null result.By the way, in the nonclassical world Dirac monopoles are connected by Dirac strings. Results from recent research in solid state physics seems to have measured effects attributable to Dirac strings. The background space, in this case, is not the vacuum of course, though I wouldn't be surprised if strings will be measured sometime soon between media separated in space with opposite magnetic charge associated with the separated media.

 

[Vanadium 50]

A perm. magnet can have a magnetic field without charge or current.

The magnetization arises from the electrons in the atom. If you got rid of electric charge you would also get rid of this permanent magnetization.

I don't dispute that people can write down a theory other than Classical Electrodynamics that permits different solutions (although I didn't follow yours). But that's not the focus of a forum called "Classical Physics".

 

[Phrak]

Vanadium, I don't disagree with you. When someone says that someone says magnetism can exist without charge, we may not be getting the whole context.

Except the bit about Dirac strings, I was speaking classically.

 

[Meir Achuz]

The magnetization arises from the electrons in the atom. If you got rid of electric charge you would also get rid of this permanent magnetization.

I don't dispute that people can write down a theory other than Classical Electrodynamics that permits different solutions (although I didn't follow yours). But that's not the focus of a forum called "Classical Physics".

Ferromagnetism is caused by the electron's magnetic moment, not its charge.

 

[Vanadium 50]

If an electron were neutral, it would have no magnetic moment.

 

[Naty1]

So magnetism exists without current, but not without charge.

 

[mburt]

A moving magnetic field can create a current, a stationary magnetic field cannot.

So to answer the question (as above), a stationary permanent magnet yields no current, but the converse is true as well. A stationary current (well, a coil with no moving electrons) yields no magnetic field.

There is a somewhat classical way to answer the question I guess

 

[kcdodd]

How do you define a moving magnetic field? A moving current?

 

[mburt]

Well an example of a moving magnetic field would be moving a permanent magnet over (or through) an electromagnetic (this would induce a current).

And by moving current, I just meant moving electrons. I stated it that way to enforce the converse statement

 

[mquirce]

The magnetism of electron mass particle, support idea that this particle is structured by two electric charge that move toward each other. It is not enough to have electric charge. neNeeded the moviment of this charge to create magnetism. This is the opinion of a layman.

 

[RedX]

Not to get overly pedantic, but it is possible for an object to have a magnetic moment without having an electric charge. Not just something like a neutron, but even the neutrino can have a magnetic moment.

Anyways, as to the OP, if you want, just add a magnetic charge and magnetic current to Maxwell's equation, and for every real problem you try to solve, there will be no magnetic charges/current around so set them equal to zero, and your beautifully symmetric Maxwell's equation reduces to the ugly ones (the ones without magnetic charge/current).

 

[mquirce]

Redx. I think that without find why electron, proton, neutron, neutrino have magnetism, the theory of particles is incomplete. Exactly your post extend the idea that all elementary particles must have structure. Sure a layman may have wrong ideas, because so is his horison, but to say that electron is a point and on the other hand to say has mass, magnetism, a infinite energy, a infinite geodesic, seems to do with thisme strange. I think that Gerlah experiment maybe has to idea.

 

[kcdodd]

So by moving magnetic field you mean a field changing strength and/or direction in time?

 

[Phrak]

If an electron were neutral, it would have no magnetic moment.

Well, maybe. A neutron has a magnetic moment. You could counter by saying that a neutron is composed of charged quarks, but this goes far afield into unknow territory. How much is orbital magnetic moment and how much is intrinsic--who knows?

However, it would be interesting to know if there are any articles that support this. The W weak force is exceptional it is the only fundamental boson with charge. That could change everything.

 

[Phrak]

If an electron were neutral, it would have no magnetic moment.

Well, maybe. A neutron has a magnetic moment. You could counter by saying that a neutron is composed of charged quarks, but this goes far afield into unknow territory. How much is orbital magnetic moment and how much is intrinsic--who knows?

However, it would be interesting to know if there are any articles that support this. The W weak force is exceptional it is the only fundamental boson with charge. That could change everything.

 

[Phrak]

If an electron were neutral, it would have no magnetic moment.

Well, maybe. A neutron has a magnetic moment. You could counter by saying that a neutron is composed of charged quarks, but this goes far afield into unknow territory. How much is orbital magnetic moment and how much is intrinsic--who knows?

However, it would be interesting to know if there are any articles that support this. The W weak force is exceptional. It is the only fundamental boson with charge. That could change everything.

 

[pallidin]

Phrak, your drinking too much coffee. You inadvertently posted the same message 3 times. :)

 

[Vanadium 50]

Well, maybe. A neutron has a magnetic moment. You could counter by saying that a neutron is composed of charged quarks, but this goes far afield into unknow territory. How much is orbital magnetic moment and how much is intrinsic--who knows

Doesn't matter. If the quarks had no charge, the magnetic moment of the neutron would be zero.

I don't understand your comment about the W; it has charge, it has a magnetic moment and it even has an electric quadrupole moment.

 

[Antiphon]

I asked my professor( he has a PhD in Particle Physics) and he said magnetism can exist independently of charges but he didn't explain why during a E&M class.
I ask this because I wonder why the speculation of magnetic monopoles if magnetism is just an effect of moving charges and there are only certain ways that charges can move through space and obviously if all of the possibilities of motion must have to been exhausted since the nobel prize in the waiting if they where found.
Why do people still speculate about magnetic monopoles existing?

Let's be precise. It takes a charge, which appears from another reference frame than the charge is in, to create a magnetic field. Once created however, it maintains an independent existence from the source.

In particle speak, if you have photons (or W/Z) you will have magnetic fields even if the charges that created them have long gone.

 

[RedX]

I don't understand your comment about the W; it has charge, it has a magnetic moment and it even has an electric quadrupole moment.

I think he's probably referring to the fact that something such as the neutrino has W⁺ + e^- self-energy, i.e., heuristically speaking, the neutrino turns into those particles and those particles recombine back to a neutrino. A magnetic field can hit the neutrino when it's one of those charged particles. The diagram of that would be much like the QED vertex correction, except the incoming and outgoing legs is a neutrino, and the internal legs would be the electron, and the internal boson between electron legs would be a W, and the external photon line can hit both the W and the electron line.

 

[Rayquesto]

I believe that Magnetism can exist independent from current because a current is formed from aligning magnetic fields which we call "magnetic Domains." Magnetism still exists, but the elctrons are all over the place. I don't know about chrage though because chrage still exists in magnetism regardless of unaligned magnetic fields.

 

[ZealScience]

Well, Gauss Law of magnetism in Maxwell's equations states that integral of magnetic flux of a closed surface is zero, or in differential form the divergence is zero. It means that magnetic monopoles don't exist, but it is just experience from former experiments, perhaps somewhere in the universe where monopoles are hiding out there.

Apart from Gauss Law, only Ampere's Law and the displacement current term is responsible for magnetic field. The two laws means only charges (current) and electric field can generate magnetism, if monopole is not a choice.

But if some day you discover monopoles, don't forget to inform Mr Nobel, he will reward you definitely.

 

[ZealScience]

I believe that Magnetism can exist independent from current because a current is formed from aligning magnetic fields which we call "magnetic Domains." Magnetism still exists, but the elctrons are all over the place. I don't know about chrage though because chrage still exists in magnetism regardless of unaligned magnetic fields.

Aren't the electrons moving fast? I think that moving electrons are generating current, though the current is not one resposible for the magnetic domains. In most cases, magnetic field is generated by magnetic moments, that's the idea from Bohr's magnetons which is quite handy in quantum mechanics. Still, I insist on magnetic monopoles, which physicists are looking for.

 

[Drakkith]

I believe that Magnetism can exist independent from current because a current is formed from aligning magnetic fields which we call "magnetic Domains." Magnetism still exists, but the elctrons are all over the place. I don't know about chrage though because chrage still exists in magnetism regardless of unaligned magnetic fields.

Magnetism cannot exist without charge. Period. Current is a flow of charges, usually electrons in a conductor. A stationary charge, in relation to an observer, is NOT creating a magnetic field EXCEPT through its intrinsic spin. In an atom the electrons are in orbitals around the nucleus, which means that the electrons are moving and thus create an additional magnetic field from that movement. The alignment of these in a permanent magnet is the source of it's magnetism.

Well, maybe. A neutron has a magnetic moment. You could counter by saying that a neutron is composed of charged quarks, but this goes far afield into unknow territory. How much is orbital magnetic moment and how much is intrinsic--who knows?

Yes, the magnetic moment is from the charged quarks in the neutron.

How do you define a moving magnetic field? A moving current?

It's not a MOVING magnetic field, it is a CHANGING magnetic field. I'm not sure what you mean by asking how do you define it.

The magnetism of electron mass particle, support idea that this particle is structured by two electric charge that move toward each other. It is not enough to have electric charge. neNeeded the moviment of this charge to create magnetism. This is the opinion of a layman

I can barely understand you, but I think you are saying we require 2 separate particles to describe electromagnetism, which isn't true.

 

[MannyP2011]

Thanks to all who replied, I'm just a second year physics major to whom half of this was out of my league. But the other half was very helpful.. thanks

 

[Rayquesto]

Magnetism cannot exist without charge. Period. Current is a flow of charges, usually electrons in a conductor. A stationary charge, in relation to an observer, is NOT creating a magnetic field EXCEPT through its intrinsic spin. In an atom the electrons are in orbitals around the nucleus, which means that the electrons are moving and thus create an additional magnetic field from that movement. The alignment of these in a permanent magnet is the source of it's magnetism.

Well, Drakkith, what is your insight as to how something contains magnetism yet doesn't contain a current or charge? I mean, if a current doesn't exist, doesn't that mean that magnetic domains don't exist, partially due to the right hand rule and the nature of directions of current and magnetic field? like the direction of the magnetic field is perpendicular to the current it produces.

 

[Drakkith]

Well, Drakkith, what is your insight as to how something contains magnetism yet doesn't contain a current or charge?

What do you mean? I specifically said magnetism cannot exist WITHOUT charge.

I mean, if a current doesn't exist, doesn't that mean that magnetic domains don't exist, partially due to the right hand rule and the nature of directions of current and magnetic field? like the direction of the magnetic field is perpendicular to the current it produces.

The magnetism produced by a current is caused by the movement of charges through the conductor. That is not the only way to produce a magnetic field though. In addition to that, all charged particles also have intrinsic "spin" which produces their magnetic moment. Also, like I said above, electrons in orbitals have further movement which produces another magnetic field. What you are talking about is only the magnetic field from moving charges.

From wikipedia:

A magnetic field is a field of force produced by moving electric charges, by electric fields that vary in time, and by the 'intrinsic' magnetic field of elementary particles associated with the spin of the particle.

 

[Rayquesto]

What do you mean? I specifically said magnetism cannot exist WITHOUT charge.

Then what is the original guy still curious about? Like How can you answer the original question that this "host" asked?

 

[ZealScience]

Are magnetic domains caused by magnetic moment of intrinsic spin? As I think charges are not "moving" in the normal sense, according to Orbital theories. What about the Bohr's magnetons?

If the string theory is true to some extent, there should be a way to generate an intrinsic property that makes the magnetic monopoles true. Or maybe the configuration of our environment is not sufficient for their to be a monopole? Probably somewhere in space the configuration can show the presence of monopoles

Just my personal views, I am just a high school student, incomplete understanding there are a lot please correct them...

 

[Drakkith]

What do you mean? I specifically said magnetism cannot exist WITHOUT charge.

Then what is the original guy still curious about? Like How can you answer the original question that this "host" asked?

What are you talking about?

Are magnetic domains caused by magnetic moment of intrinsic spin? As I think charges are not "moving" in the normal sense, according to Orbital theories. What about the Bohr's magnetons?

Partly. It is both the magnetic moment of the particle and the movement in it's orbital I believe.

If the string theory is true to some extent, there should be a way to generate an intrinsic property that makes the magnetic monopoles true. Or maybe the configuration of our environment is not sufficient for their to be a monopole? Probably somewhere in space the configuration can show the presence of monopoles

I'm not versed enough in String Theory to answer that, sorry.

 

[ZealScience]

Partly. It is both the magnetic moment of the particle and the movement in it's orbital I believe.

I got some questions here. First are electrons really "moving" in the old mechanical way? Then it will face the same problem as Rutherford's model, that if electrons are moving in electric field it will generate a spherical wave and causing radiation.

In new theories from quantum mechanics, the electrons behaves in a possibility wave function manner, but does elctron cloud also create E field apart? Or other quantum number(s) like the magnetic angular moment number affects the magnetic field?

 

[mquirce]

Drakkith. I am not able to debate . I only want an assertion: Can or can not be magnetism in an elementaery particle without the moviment of the charge in circular track? As for my opinion that structure of electron has two charge this derive from the idea that one charge can,t stand without the partner. And this for all elementary particles. Sorry if my english is terrible.

 

[Drakkith]

I got some questions here. First are electrons really "moving" in the old mechanical way? Then it will face the same problem as Rutherford's model, that if electrons are moving in electric field it will generate a spherical wave and causing radiation.

In new theories from quantum mechanics, the electrons behaves in a possibility wave function manner, but does elctron cloud also create E field apart? Or other quantum number(s) like the magnetic angular moment number affects the magnetic field?

The electrons are not moving in a classical sense, but they still move in their orbitals around the nucleus. I think you could say that their wavefunction isn't stationary. The exact quantum numbers for each electron would alter the way it creates a magnetic field. Some electrons have more angular momentum around the nucleus than others and such.

Drakkith. I am not able to debate . I only want an assertion: Can or can not be magnetism in an elementaery particle without the moviment of the charge in circular track? As for my opinion that structure of electron has two charge this derive from the idea that one charge can,t stand without the partner. And this for all elementary particles. Sorry if my english is terrible.

The magnetic moment of a particle doesn't require it to move in a circular track. The magnetic field is from that particles inherent rotation, known as its spin. And I can say with 100% certainty that your view of 2 charges in one electron is incorrect according to science.

 

[ZealScience]

The electrons are not moving in a classical sense, but they still move in their orbitals around the nucleus. I think you could say that their wavefunction isn't stationary. The exact quantum numbers for each electron would alter the way it creates a magnetic field. Some electrons have more angular momentum around the nucleus than others and such.

Do you mean quantum jump here? But we can never observe the motion of electrons according to uncertainty principal. Do we really know how it is done? What about the angular quantum numbers, they are parameters of Schrodinger's equations. But can Magnetic Domains Being predicted by Schrodinger? Please explain, I am amateur, thank you!

 

[Drakkith]

Do you mean quantum jump here? But we can never observe the motion of electrons according to uncertainty principal. Do we really know how it is done? What about the angular quantum numbers, they are parameters of Schrodinger's equations. But can Magnetic Domains Being predicted by Schrodinger? Please explain, I am amateur, thank you!

Why can't we? We cannot know the exact position AND momentum of the electrons, no, but we can see their motions to a certain degree of accuracy. Also, no, I don't mean quantum jump, I'm simply talking about motion in its orbital.

I don't know enough about Schrodinger equations to answer the other part of your question however, sorry!

 

[Phrak]

Phrak, your drinking too much coffee. You inadvertently posted the same message 3 times. :)

Good grief!

 

[Antiphon]

Magnetism cannot be created without a charge.

Once created, magnetism can exist without a charge.

Take a positron-electron pair and annihilate them. The charges are gone, the magnetism persists potentially for ever more.

 

[Drakkith]

Magnetism cannot be created without a charge.

Once created, magnetism can exist without a charge.

Take a positron-electron pair and annihilate them. The charges are gone, the magnetism persists potentially for ever more.

How does it exist if the charges are gone?

 

[pallidin]

Yes, I also would like to see some evidence on that claim of persistent magnetism.

 

[kcdodd]

E&M radiation through conservation of energy.

 

[RedX]

You can always have a constant magnetic field and it will be a solution to Maxwell's equations without any sources.

 

[Drakkith]

E&M radiation through conservation of energy.

The magnetic field exists because of the electric field.

You can always have a constant magnetic field and it will be a solution to Maxwell's equations without any sources.

Perhaps, but that doesn't mean you can have a magnetic field that doesn't have a source.

 

[RedX]

Perhaps, but that doesn't mean you can have a magnetic field that doesn't have a source.

You're probably right. You can sort of argue it by symmetry. If the universe did have a constant magnetic field, then it would have to be in some direction. But assuming the universe is isotropic, then everything is the same in all directions, so this field would have to be zero.

Actually, I think you can only spontaneously break scalar fields and not vector (or spinor) fields. So it's actually Lorentz symmetry that would prevent a constant magnetic field in empty space, as there exists no unitary operator U such that:

\langle 0| U^{\dagger} F_{\mu \nu} U |0 \rangle=\langle 0| F_{\mu \nu}|0 \rangle=\Lambda_{\mu&#039;}^{\mu} \Lambda_{\nu&#039;}^{\nu}\langle 0| F_{\mu \nu}|0 \rangle
for all Lorentz transformations Lambda (U operated on the vacuum yields the vacuum is the assumption).

It seems the only way around this is to have an operator that doesn't change in the adjoint representation of the Lorentz group, i.e., one that doesn't transform like:

O \rightarrow U^{\dagger} O U
which leads to the question do all operators must transform like that?

 

[Drakkith]

I don't understand what the math has to do with this. I thought it was a simple fact that a magnetic field needed a source, which is charged particles.

 

[RedX]

I don't understand what the math has to do with this. I thought it was a simple fact that a magnetic field needed a source, which is charged particles.

I think you're assuming that fields vanish at infinity. If that's the case, then you're definitely right. But if you just take Maxwell's equations without any boundary conditions, then there are solutions where the field doesn't vanish at infinity, in particular constant fields (since the equations all involve derivatives of fields).

I just thought it was interesting that there's a quantum reason that electric and magnetic fields must vanish at infinity, that \langle 0 |F_{\mu \nu} | 0 \rangle has to equal zero. If the electric and magnetic fields were scalar, then it is not necessarily true that the fields must vanish at infinity, or that the fields don't exist without sources.

But this is getting to far away from classical physics. Maxwell's equations+boundary condition of vanishing at infinity should be enough to establish that the fields vanish without a source.

 

[pallidin]

...that the fields vanish without a source.

True, but not instantly. There is a delay. Assumed at C.
That is, a magnetic source can cease to exist, but, the magnetism DOES NOT instantly cease.

The same is "assumed" with gravity. If the Sun were to suddenly vanish, the Earth would still be affected by it's gravity for 8+ miniutes even though the sun no longer actually exists.