Can magnetism exist independently of current or charge?

[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:

$$\langle 0| U^{\dagger} F_{\mu \nu} U |0 \rangle=\langle 0| F_{\mu \nu}|0 \rangle=\Lambda_{\mu'}^{\mu} \Lambda_{\nu'}^{\nu}\langle 0| F_{\mu \nu}|0 \rangle$$
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.

 

[Antiphon]

A pair of opposite charges annihilate releasing a pair of gamma ray photons.

The photons' trajectories are bent into large circles by a distribution of neutron stars.

The electric and magnetic fields (as photons) travel around the same neighborhood of neutron stars for 20 billion years after the charges have ceased to exist.

I hope this is thought experiment enough to convince anyone that there can be magnetism long after the source charge has gone.

 

[Drakkith]

I don't think the argument was that magnetic fields cannot exist after their sources were gone, but that magnetism needed no charge as a source. At least that was what I got. Two charges that annihilate still have a magnetic and electric field that is extending outwards at c, but as the fields no longer have an existing source, no further field is created beyond what already existed before the annihilation.

 

[Khashishi]

Magnetism can exist independently from charges in the form of electromagnetic waves. Electromagnetic waves can be formed by annihilation of matter/antimatter, presumably without needing charges to exist.

 

[Drakkith]

Magnetism can exist independently from charges in the form of electromagnetic waves. Electromagnetic waves can be formed by annihilation of matter/antimatter, presumably without needing charges to exist.

EM Waves are made up of electric AND magnetic fields. I believe they are both the source of each other?

 

[Antiphon]

I don't think the argument was that magnetic fields cannot exist after their sources were gone, but that magnetism needed no charge as a source. At least that was what I got. Two charges that annihilate still have a magnetic and electric field that is extending outwards at c, but as the fields no longer have an existing source, no further field is created beyond what already existed before the annihilation.

Ah, this is a much more interesting question.

If you start off in a universe with zero fields and zero charges you still have zero-point magnetic fields. But let's ignore that.

There's no obvious way to create any EM fields under these conditions.

But there may be an unobvious way- via Hawking radiation. A charge-neutral black hole in an empty universe will radiate EM fields without the presence of charge.

 

[Drakkith]

Ah, this is a much more interesting question.

If you start off in a universe with zero fields and zero charges you still have zero-point magnetic fields. But let's ignore that.

There's no obvious way to create any EM fields under these conditions.

But there may be an unobvious way- via Hawking radiation. A charge-neutral black hole in an empty universe will radiate EM fields without the presence of charge.

I don't know much about black holes, but wouldn't it only be charge neutral when equal amounts of + and - charges have fallen in? (Ignoring the problem of electric fields propagating from a black hole, if that is a problem)

Also, isn't hawking radiation the result of the creation of real particles from virtual particles? Which are charged?

 

[kcdodd]

I have also asked myself if sources can exist without any fields. It seems clearly they cannot. One cannot have an electron without any electric or magnetic field. It is intrinsic to what an electron is. However, one can have EM fields without electrons. A charged particles does not seem intrinsic to EM fields the way EM fields is intrinsic to charged particles. Also, field energy can give rise to the creation of charged particles via pair production, so it really begs the question of which is more fundamental; source or field.

 

[Drakkith]

I have also asked myself if sources can exist without any fields. It seems clearly they cannot. One cannot have an electron without any electric or magnetic field. It is intrinsic to what an electron is. However, one can have EM fields without electrons. A charged particles does not seem intrinsic to EM fields the way EM fields is intrinsic to charged particles. Also, field energy can give rise to the creation of charged particles via pair production, so it really begs the question of which is more fundamental; source or field.

Is the field produced by a charged particle and the alternating fields in EM radiation different or the same? (If that makes any sense)

I would say that both the EM fields in a photon, and the fields from a charged particle both require SOME source. What produced the initial radiation from the beginning of the universe? Was there a "source"?

 

[kcdodd]

I am not quite sure if one can distinguish fields like that. Anywhere there is no source then the field automatically obeys the source-free maxwell equation, whether or not one considers the field to be "sourced" somewhere else. Classically one might suppose that a constant field must be due to sources somewhere since there would be no other way for it to arise. However, that all depends on the time-scale one is considering and what they consider "constant". Clearly no arrangement of atoms one can create can create a truly constant field, since they just created them. How would one tell the difference between a constant field and a field that just happens to have a very low frequency and/or very long wavelength. QED wise the fields break down to photons anyway.

As to the beginning of the universe; who knows. I think current theory holds that matter (aka "sources") came after the radiation. Or at least was radiation dominant. Before radiation I don't think we know, because there is no radiation from that time to look at.

 

[vanhees71]

I guess somebody has already answered in this direction within this thread, but let me try again:

From a fundamental point of view all matter consists of elementary particles. The sources of the electromagnetic field are electric charge distributions, current densities, and magnetic moments of the elementary particles. Of course, these particles form larger compounds like atomic nuclei, atoms, molecules, and finally condensed matter as we know it, and the macroscopic properties are given as the appropriate averages over all these microscopic degrees of freedom.

This leads to an effective description of the macroscopic electromagnetic properties with sources given by the charge distributions, current-density distribution, and the magnetization of matter. The magnetization can formally be subsumed into the effective current-density distribution:

$$\vec{j}_{\text{eff}}=\vec{j}_{\text{free}}+ \vec{\nabla} \times \vec{M}.$$

The Maxwell equation (in Heaviside-Lorentz aka. rationalized Gaussian units), related to this reads

$$\vec{\nabla} \times \vec{H}-\frac{\partial \vec{D}}{c \partial t}=\vec{j}_{\text{eff}}.$$

 

[Antiphon]

I don't know much about black holes, but wouldn't it only be charge neutral when equal amounts of + and - charges have fallen in? (Ignoring the problem of electric fields propagating from a black hole, if that is a problem)

Also, isn't hawking radiation the result of the creation of real particles from virtual particles? Which are charged?

Actually in principle you could create a black hole by aggregating enough uncharged particles. Neutrons come to mind but if you want to be really severe about it, make a black hole using only Neutrinos. A LOT of Neutrinos.

Hawking radiation can produce all kinds of particles but let's just work with the photons here.

So you start with an uncharged universe filled with an immense quantity of neutrinos. They colocate by random chance so that a black hole forms. This black hole then emits photons by Hawking radiation, and Never was a single charge present.