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### Author Topic: What particle carries magnetic field?  (Read 40677 times)

#### manjit

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##### What particle carries magnetic field?
« on: 09/11/2008 19:03:22 »
Hi All!

I have tried to find out about the nature of the particles that carries magnetic field (not EM filed), but have not managed it. Can someone of you there explain what particles carries magnetic field if it is carried by particles?

Thanks for all inputs!
manjit

#### DoctorBeaver

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##### What particle carries magnetic field?
« Reply #1 on: 09/11/2008 23:19:46 »
Magnetic fields are not produced by particles. Photons mediate the electromagnetic force, but that is not the same as a field.

I don't really understand the nature of fields, but I think a field is area that has the potential to allow bosons that mediate the force associated with that field to actually do so. The greater the potential of the field, the more the bosons do their job and the force is stronger.

I dare say 1 of our physics gurus will correct me.

#### lyner

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##### What particle carries magnetic field?
« Reply #2 on: 10/11/2008 10:12:58 »
To get down to basics. A Field is the gradient of Energy (potential).
Change in potential = field times distance moved
or, more familiarly,
Work = Force X distance
In a strong field, the potential changes rapidly with distance and vice versa.
If a field changes or something moves along the field, some energy is transfered and the potential changes.
With electromagnetic fields, photons are involved when there are changes (i.e the photon 'carries' the energy). The 'magnetic field' in the original post implies no change (?) so the corresponding photon would have zero frequency and no energy. BUT, as it wouldn't have always been there and it won't always be there so it must have involved some change with time. There would be a finite frequency associated with this photon plus some associated Electric Field.
« Last Edit: 10/11/2008 10:25:24 by sophiecentaur »

#### DoctorBeaver

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##### What particle carries magnetic field?
« Reply #3 on: 10/11/2008 11:44:34 »
SC - is this more-or-less correct then?

Quote
...a field is area that has the potential to allow bosons that mediate the force associated with that field to actually do so. The greater the potential of the field, the more the bosons do their job and the force is stronger.

In very simplistic terms, of course.

#### lyner

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##### What particle carries magnetic field?
« Reply #4 on: 10/11/2008 15:15:58 »
I don't feel qualified to comment on what you're saying. You are using terms like potential and field in a way I'm not familiar with.
I know the word 'mediate' is popular but I'm not really sure what it means in this context.
We need to phone a friend, I think.

#### DoctorBeaver

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##### What particle carries magnetic field?
« Reply #5 on: 10/11/2008 15:34:03 »
"Mediate" is the term I've seen used in most physics textbooks to mean "carrying the force".

I mean "potential" in layman's terms - i.e. it has the potential of doing something.

#### lyner

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##### What particle carries magnetic field?
« Reply #6 on: 10/11/2008 18:22:45 »
OK - potential has really the same meaning for me except it refers specifically to the 'potential to do work'.
Gravitational potential is the energy / work in raising 1kg of mass and electrical potential is the energy involved in moving 1 Coulomb of charge from place to place.
For 'mediate' I would take mild issue with the expression 'carry the force'; it implies a piece of rope connecting two objects.  I think 'mediate' is a word that was deliberately introduced so that they wouldn't have to cope with preconceptions which other words might bring with them.
Mediating, politically and socially, means bringing together or coupling so I can see where they're coming from. Personally, I go for Energy rather than Force in any explanation because Force, on its own doesn't necessarily mean that anything is happening or changing; the force has to move (work done) for that to happen.
I could happily say that "Photons mediate the electromagnetic interaction of two charges", for instance.

I wish that friend would answer the 'phone!

#### DoctorBeaver

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##### What particle carries magnetic field?
« Reply #7 on: 10/11/2008 18:39:56 »
To nediate means "To act as a go-between or arbiter". A go-between seems apt.

#### Soul Surfer

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##### What particle carries magnetic field?
« Reply #8 on: 10/11/2008 19:25:51 »
To go back to answering the original question posed.

Magnetic monopoles have been proposed but are unlikely to exist.

All charged fermions (particles with a half integer spin) like electrons and the components of protons have a magnetic field like a little bar magnet and it is this that is used to control their spin directions.

I also think that the neutral fermions  like neutrinos also have magnetic fields associated with them that are seen as part of "neutral currents" in certain rare high energy weak interactions.

so many particles carry magnetic fields as many particles carry electrical charges.

This can more easily be understood if one considers atoms with highly unbalanced residual spins  (like iron and a few other atoms)  These can form permanent magnets  where a lot of the residual fields can be aligned and locked in a similar direction to create a large overall magnetic field.
« Last Edit: 10/11/2008 19:30:43 by Soul Surfer »

#### lyner

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##### What particle carries magnetic field?
« Reply #9 on: 10/11/2008 21:38:00 »
Having read the question again I am not really sure what it is really asking. The magnetic field of a fermion is a dipole - so that could just be the answer - except does it actually 'carry' the field?
I interpreted it more in terms of the 'mediate' word - implying the idea of causing the field to produce a force on something else. Hence my photon idea.

#### DoctorBeaver

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##### What particle carries magnetic field?
« Reply #10 on: 10/11/2008 23:09:37 »
Quote
I interpreted it more in terms of the 'mediate' word - implying the idea of causing the field to produce a force on something else. Hence my photon idea.

Me too

#### yor_on

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##### What particle carries magnetic field?
« Reply #11 on: 11/11/2008 00:35:45 »
"
Permanent magnets

A few elements -- especially iron, cobalt, and nickel -- are ferromagnetic at room temperature. When quantum mechanics and the Pauli Exclusion Principle are accounted for, the electrical energy within these atoms is found to be lower if the magnetic moments of the valence electrons are aligned. This makes them ferromagnetic.

Every ferromagnet has its own individual temperature, called the Curie temperature, or Curie point, above which it loses its ferromagnetic properties. This is because the thermal tendency to disorder overwhelms the energy lowering due to ferromagnetic order. A perfectly aligned ferromagnet is said to have long-range order because all of its atoms have their magnetic moments pointing in the same direction.

Real ferromagnets are not perfectly aligned, but rather contain perfectly aligned regions, called magnetic domains, which have their own magnetization directions. A long bar magnet appears to have a north pole at one end and a south pole at the other. Near either end the magnetic field falls off inversely with the square of the distance from that pole.

For a magnet of any shape, at distances large compared to its size, the strength of the magnetic field falls off inversely with the cube of the distance from the magnet's center."

And as you seem to be wondering about 'magnetic domains'

but if you're wondering if there is a explanation that really describe the phenomena for what it is?
No, not that I know at least:)

----------

" In QED, forces between particles of matter are mediated by the collision of photons with electrons and the accompanying momentum transfer.

So streams of photons must leave each of the two magnets of (Two horse shoe magnets placed against each other S/North and N/South, with a copperplate placed in the middle, separating their 'ends' from each other ) spontaneously and forever, and then pass through a copper plate, finally colliding with electrons at the surface and deep inside the opposite horseshoe magnets.

A simple collision between two articles produces repulsion, therefore in order to generate attraction between the magnets, the photons must navigate around the magnets, turn and strike them in the back.

This mechanism is so ludicrous that it will not be found discussed in textbooks. Nor will most professors mention it to a class of students."

I would dearly like to know if there is any good explanation of this phenomena :)
........

Ah, I used to have a slightly less controversial source for this last one.
but I can't find it anymore :(
I found this one instead (not as innocent presumably)
So I will have to reread it to see how they think, but.
As it mentions the experiment I will use it.

It's more easy to see the idea graphically.
http://www.worldscibooks.com/phy_etextbook/6087/6087_chap1.pdf
« Last Edit: 11/11/2008 01:21:28 by yor_on »

#### lyner

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##### What particle carries magnetic field?
« Reply #12 on: 11/11/2008 13:38:22 »
Yor_on
Quote
This mechanism is so ludicrous
It's only ludicrous is you choose to think of photons as being little bullets. They have to occupy a region which is at least as big as the wavelength involved (I could rant on for ever about this) and, for mechanical collisions, the time constant is very large so the associated photon frequency is very low and the wavelength huge.  The photon can easily be regarded as sloshing all over the objects involved in the collision.
We all know that Professors are whimps and avoid controversy in their lectures.
Also, just 'cos you're a prof doesn't mean you've thought absolutely everything through properly - there just isn't time.

But, to relate this to the original question - we're still talking about Electric field effects too.

#### yor_on

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##### What particle carries magnetic field?
« Reply #13 on: 11/11/2008 14:12:29 »
Sophie.
you say "They have to occupy a region which is at least as big as the wavelength involved "
And by setting a low time constant you will get a large wave in 'space'.
And so you are invoking the uncertainty principle if I read you right?
A little like tunneling then?

'Rant' on Sophie, I'm curious:)
Btw: Your answer makes a certain 'sense', but I want more examples::))

#### lyner

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##### What particle carries magnetic field?
« Reply #14 on: 11/11/2008 14:21:05 »
I'm referring to the fact that diffraction is a fundamental limitation where waves are concerned. You need to consider waves if you want to know whether a photon is likely to 'turn up' somewhere or not.
In the same way that we are more than happy to talk in terms of an electron wave function when it is in a bound state then I think it is quite in order to talk waves when there is an interaction with a photon. That implies that we should / can treat the way this photon interacts with this magnet as if the photon is a wave, if we want to describe how things work.
Isn't that the most reasonable thing you've read this afternoon?

#### JP

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##### What particle carries magnetic field?
« Reply #15 on: 11/11/2008 18:55:00 »
This is slightly off-topic, but I saw a talk by Sir Peter Knight recently where he discussed some recent work on doing a rigorous quantum-mechanical calculation of single-photon diffraction from 1-slit and 2-slit setups.  The punchline was that it matched up with what you get from using classical waves.  The calculation was so computationally intensive to do that you'd never want to use the photon treatment for diffraction in practice, however.

#### lightarrow

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##### What particle carries magnetic field?
« Reply #16 on: 11/11/2008 19:04:44 »
Hi All!

I have tried to find out about the nature of the particles that carries magnetic field (not EM filed), but have not managed it. Can someone of you there explain what particles carries magnetic field if it is carried by particles?

Thanks for all inputs!
manjit
In Maxwell's equations you find:

div E = -ρ/ε0

it means that electric charges (ρ is their density) are responsible of static electric field (E).
But there is also written:

div B = 0

(B is the magnetic field)
which means that there are not magnetic charges.

#### lyner

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##### What particle carries magnetic field?
« Reply #17 on: 11/11/2008 19:53:52 »
This is slightly off-topic, but I saw a talk by Sir Peter Knight recently where he discussed some recent work on doing a rigorous quantum-mechanical calculation of single-photon diffraction from 1-slit and 2-slit setups.  The punchline was that it matched up with what you get from using classical waves.  The calculation was so computationally intensive to do that you'd never want to use the photon treatment for diffraction in practice, however.
Nothing would surprise me less.

#### lyner

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##### What particle carries magnetic field?
« Reply #18 on: 11/11/2008 19:54:59 »
Well put, lightarrow, as usual.

#### manjit

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##### What particle carries magnetic field?
« Reply #19 on: 12/11/2008 20:16:37 »
Many warm thanks to all of you who has spent their time and effort to try to explain it. I must admit that most of the responses are above my ability to understand, but I understand  a bit more now than before.
manjit

#### erickejah

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##### What particle carries magnetic field?
« Reply #20 on: 13/11/2008 03:39:47 »
really interesting.

#### yor_on

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##### What particle carries magnetic field?
« Reply #21 on: 13/11/2008 11:45:27 »
Ah Sophie, you are a voice of reason:)
And I'm not joking there.

How would I dare disagree with such logic?
But I will try, not so much disagreeing, more like not being fully satisfied:)

Tell me Sophie, if you pinch your self, does it not hurt?
And that skin of yours, is it then not different from bone, from stone?

So if all is explainable as waves what about invariant mass?

#### lyner

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##### What particle carries magnetic field?
« Reply #22 on: 13/11/2008 12:53:42 »
All I was implying is that treating photons as little bullets is very blinkered. Treating them as small helpings of Energy (the original reason for introducing the concept), constrained by a wave gives rise to no problems yet resolves a lot of apparent paradoxes.

Where does invariant mass prove to be a problem in this respect? Perhaps you could include 'what mass is' in that explanation.

#### yor_on

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##### What particle carries magnetic field?
« Reply #23 on: 13/11/2008 15:56:16 »
Sophie, to me it is a constant source of consternation.
Most things in QM can be explained, as you write, as "small helpings of Energy (the original reason for introducing the concept), constrained by a wave".
But then we have 'matter' (invariant mass) and to me it is to its 'nature' definitely unlike any of those concepts:)
It's not energy, even though it can be 'expressed' as it and 'transformed' into it.
It have an equivalence, but is a totally different 'state' if you see how i think.
And I can't reconcile it with waves only.

And I would love to be able to "include 'what mass is"
:)

#### lightarrow

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##### What particle carries magnetic field?
« Reply #24 on: 13/11/2008 18:27:41 »
Sophie, to me it is a constant source of consternation.
Most things in QM can be explained, as you write, as "small helpings of Energy (the original reason for introducing the concept), constrained by a wave".
But then we have 'matter' (invariant mass) and to me it is to its 'nature' definitely unlike any of those concepts:)
It's not energy, even though it can be 'expressed' as it and 'transformed' into it.
It have an equivalence, but is a totally different 'state' if you see how i think.
And I can't reconcile it with waves only.

And I would love to be able to "include 'what mass is"
:)

Take a ray of light and confine it in a fixed space (for ex. a box). Now the light has mass.

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##### What particle carries magnetic field?
« Reply #24 on: 13/11/2008 18:27:41 »