What exactly is magnetism, anyway?

  • #1
homedoc
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After carefully reading textbooks, research papers and a lot of forums, I find myself more confused than ever regarding the composition of magnetic fields. So please let me ask some (hopefully) very simple questions:

(1) Do we or do we not know exactly how magnetic fields arise and dissipate?

(2) If we do, I want to confirm that they are composed solely of photons as stated by many erudite authors. What distinguishes magnetic photons from other photons? Is it just wavelength/energy or are there other differences between magnetic photons and, say, light photons.

(3) The reason for my inquiry is that I am trying to understand the behavior of magnetic fields. So maybe that can be accomplished even without knowing the answers to the above questions. Apparently, like other photons, magnetic photons exhibit momentum. So if we were to reproduce the old children's toy (a four paddle spinning pinwheel suspended on a needle in a vacuum with one side of each paddle painted black and the other white) using non-magnetic materials, would we be able to see it spinning as well?

(4) In the magnetic field of a bar magnet, do the photons circulating within the field all originate from within the magnet?

(5) If we were to "sink" the north pole of such a magnet, by sticking it onto a very large ferromagnetic surface, like the hull of a ship, would all the photons that enter the south end of the magnet also originate within the magnet, or would other magnetic photons from the Earth's magnetic field flow into the south end of the magnet?

(6) How exactly do magnetic fields interact? If we were to image the magnetic field of a bar magnet, and then place the north end of a second bar magnet in proximity to the north end of the first magnet, would we be able to observe distortions in the field?

(7) Last, can you refer me to a good textbook or other source of knowledge that I can study to get a better understanding of magnetic field interactions?

Thank you all very much in advance for the effort I know you will have to expend in answering these questions. I am grateful.
 
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  • #2
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Do we or do we not know exactly how magnetic fields arise and dissipate?
We do. We have a theory, QED, which explains all known EM phenomena to date.


What distinguishes magnetic photons from other photons?
There are no magnetic photons. Magnetism is part of electromagnetism, and photons are excitations of the electromagnetic field. You cannot separate them as being one type or another.

I am trying to understand the behavior of magnetic fields
Are you proficient in both Maxwell’s equations and special relativity? If not then I would start there before learning QM.
 
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  • #3
Drakkith
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(2) If we do, I want to confirm that they are composed solely of photons as stated by many erudite authors.

The magnetic field is one component of the electromagnetic field. The EM field is not composed of anything. It's not composed of matter nor is it composed of energy. The EM field is a fundamental 'building block' in the universe and it facilitates the interaction of charged particles. It's like asking what an electron is made out of. An electron isn't made out of anything other than itself. It's a fundamental particle that makes up other things.

What distinguishes magnetic photons from other photons?

There are no such things as 'magnetic photons'. Photons are electromagnetic in nature, not solely electric or magnetic.

(4) In the magnetic field of a bar magnet, do the photons circulating within the field all originate from within the magnet?

There are no photons circulating within the field. If you move the magnetic you'll get an EM wave, which will be composed of photons and will move outwards from the magnet, but in the stationary field there are no photons moving or flowing about.

(5) If we were to "sink" the north pole of such a magnet, by sticking it onto a very large ferromagnetic surface, like the hull of a ship, would all the photons that enter the south end of the magnet also originate within the magnet, or would other magnetic photons from the Earth's magnetic field flow into the south end of the magnet?

Photons are not flowing into and out of the magnet. The magnetic field lines only represent regions of identical magnetic field strength, much like how contour lines on a topographic map represent regions of identical elevation. The arrows that we usually write as going from north to south are pointed that way because of convention, not because of the underlying fundamental physics. We could draw them the other way around, modify our equations, and we'd come out with identical results.

(6) How exactly do magnetic fields interact? If we were to image the magnetic field of a bar magnet, and then place the north end of a second bar magnet in proximity to the north end of the first magnet, would we be able to observe distortions in the field?

Yes. The magnetic fields would add together at each point in space. However, since the magnetic field has both a magnitude and a direction at every point, some of these will add positively and some will add negatively. In other words, you'll end up both subtracting and adding depending on how the two magnets are oriented.
 
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  • #4
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Are you proficient in both Maxwell’s equations and special relativity? If not then I would start there before learning QM.
Side question: What is the best source to read on Maxwell's equations?
 
  • #6
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Feynman couldn't explain it.
Sure he could. He just couldn’t do it in terms of anything else. He had to use math tailored specifically for the purpose to explain it.

I think that virtual photons are real and their propagation is one of the laws of the Universe, but then I'm a theoretician.
How many theoretical physics papers have you published and in which journals?
 
  • #7
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How many theoretical physics papers have you published and in which journals?

:bow:
 

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