What exactly is magnetism?

[Ranowa]

I'm pretty sure I'm going way more indepth into this topic than I need to (I'm a pre med, neurosci major) but the way I've always understood concepts that troubled me was going to the quantum level. I'm trying to do the same with this.

 

I read a previous thread on these forums on the matter, as well as a few other papers, and basically what I'm going after is conformation that I'm thinking about this correctly. So:

 

We don't yet have a thorough understanding of what exactly magnetism is. The best way to explain it seems to be the idea of virtual photons being emitted from electrons caught within a magnet's range of influence, or field. The field is infinite, but its effects become so minute over increasing distance that they are negligible in most circumstances. The path of the virtual photons is identical to the direction of the magnetic force, indicating that the virtual photons are the reason there is a force at all. I haven't seen anyone really explain, though, what actually a magnet is- why that block of iron can cause these virtual photons to come into existence whereas my physics textbook just sits there like a lump. Is this something we don't know yet?

[swansont]

Magnetism is what electrostatics looks like if there is relative motion involving a charge. Electrons are charged and have intrinsic angular momentum, so they mimic what a spinning charge would do, and that manifests itself as having a magnetic moment. However, if the orientation of electron spins is random, these effects cancel. Only in a few materials do we see an ability for these fields to add up, or to be aligned by an external field. You need unpaired electrons so there isn't cancellation inherent in the atom and the material has to have a structure where the alignment can occur.

 

Electric current gives a magnetic field, too — that's what the electric field becomes when the charges physically move.

[Ranowa]

In the first thing that I read, it said electron spin and angular momentum on a quantum level only apply on paramagnetism, though- that we've managed to use He nuclei to prove that magnetic fields still can arise without electron spin. Was this incorrect?

[swansont]

In the first thing that I read, it said electron spin and angular momentum on a quantum level only apply on paramagnetism, though- that we've managed to use He nuclei to prove that magnetic fields still can arise without electron spin. Was this incorrect?

 

He is diamagnetic, which is a different flavor of effect from what we normally observe in magnetism Unless you have some other effect in mind, in which case could you provide a link?). In diamagnetism the electrons are responding to an external field, and repel regardless of their spin orientation. It's an exceedingly weak effect*, and is only noticeable if the material is not ferromagnetic (which is what I was describing) or paramagnetic, which is an effect where the material is attracted owing to the induced alignment. Neither para- or diamagnetic effects are permanent — they go away when the external field is turned off.

 

*unless you have a superconductor.

[Ranowa]

Ahh. That distinction seems like something that original source should've mentioned I'm assuming I won't need a good understanding of diamagnetism for my joke of an introductory physics course!

 

Was I correct in my original guess that the virtual photons are responsible for the magnetic force,or was that a little off as well?

[swansont]

Ahh. That distinction seems like something that original source should've mentioned I'm assuming I won't need a good understanding of diamagnetism for my joke of an introductory physics course!

 

Was I correct in my original guess that the virtual photons are responsible for the magnetic force,or was that a little off as well?

 

 

Diamagnetism is more of an advanced topic, but makes for fun demonstrations.

 

Virtual photon exchange is the mechanism for the electromagnetic interaction, but that, too, is a more advanced topic.

[pavelcherepan]

Here are a couple of really good videos from two of the most popular science channels on Youtube. The first video explains how permanent magnets work and the second one explains how special relativity helps understand electromagnetism. Check them out, hopefully they will answer most of your questions:

 

https://www.youtube.com/watch?v=hFAOXdXZ5TM

 

https://www.youtube.com/watch?v=1TKSfAkWWN0

Edited October 15, 2015 by pavelcherepan

[Mike Smith Cosmos]

Here are a couple of really good videos from two of the most popular science channels on Youtube. The first video explains how permanent magnets work and the second one explains how special relativity helps understand electromagnetism. Check them out, hopefully they will answer most of your questions:

 

https://www.youtube.com/watch?v=hFAOXdXZ5TM

 

https://www.youtube.com/watch?v=1TKSfAkWWN0

These two videos , although put in a cartoon style of presentation , give amazing insight into the innermost and practical effects of both electric charge and magnetic moment .

 

Very good presentation even though in a light hearted style .

 

It still leaves one wondering what the bedrock nature of electrical charge and magnetic moment really ' IS' ?

 

Mike

[imatfaal]

[timo]

A bit in a rush, but two comments:

- Saying that magnetism wasn't really understood is wrong. At least in the sense as claiming that houses were not understood is wrong: Of course there are details about houses that are not understood if you dig deep enough, but no one would seriously say we haven't understood houses.

- A good way forward to understanding magnetism is to forget about virtual photons. The way to go forward is to first understand basic magnetostatics, then classical electrodynamics. Neither of those has to do with virtual photons. Virtual photons arise in a particular approach to quantum electrodynamics (namely the perturbative one). And I have yet to be demonstrated how any of this helps in understanding what one would conventionally call magnetism.

[swansont]

I absolutely agree. You don't want to jump into advanced quantum theory in dealing with this. But I think you want to look at relativity, in order to understand why electric fields and magnetic fields are lumped into the same area of study.

[Mike Smith Cosmos]

From my small corner :-

 

I understand there is some form of rotational symmetry ' afoot ' which produces a force. This or these are known as "Gauge forces or Gauge symmetry ". Namely we are looking at the same thing from different rotational symmetry, but in so doing we notice, or experience , a force between the two ' views' of the real nature of Reality . So maybe the more fundamental view is ' Electro-Magnetic ' in nature . Then we view or experience the forces from different rotational symmetry , to experience either ' electric ' or ' magnetic ' 'phenomenon' .

 

See Prof Lee Smolin Perimeter Institute (Canada)

 

link :- Guage Theory https://en.m.wikipedia.org/wiki/Gauge_theory

 

Also link :- Prof Lee Smolin . https://en.m.wikipedia.org/wiki/Lee_Smolin

 

Mike

 

Ps if you like maths " loop quantum gravity " should keep you quiet for a while . Link :-

 

https://en.m.wikipedia.org/wiki/Loop_quantum_gravity

 

Edited October 15, 2015 by Mike Smith Cosmos

[DrP]

QUOTE SWANSONT: "electric fields and magnetic fields lumped into the same area of study"

 

I though it was Maxwell that done this with his equations? Mathematically at least.