# Magnetism

Does anyone know how/why magnetism works? I’ve searched around for quite some time but have found nothing about how and why magnetic objects behave like they do.

How Stuff Works has a fair article about it.

You can also try the Wikipedia article, in the Sources of Magnetism section, or this hyperphysics page.

How much detail do you want? Classical, relativistic, or quantum field theory?

To answer literally the exact question you asked (does anyone know…), more is known about how electromagnetism works than anything else in the Universe. Quantum electrodynamics is the most thoroughly-tested theory in all of science.

Chronos, since you’re offering, is there a classical (nonrelativistic) explanation of how magnetism works?

Nah, not really. It’s a bit of a mystery now that you mention it. Maybe someone should look into it…

Sure. Magnets have a north pole and a south pole, and like poles repel and unlike poles attract. The poles can cancel out, and if you break a magnet in half, new poles form in the middle so that each piece still has one of each pole. If you’d like, you could also go into a phenomenological description of things like how the force falls of with distance.

Now, you won’t get any coupling between electricity and magnetism in this model: Any self-consistent model of magnetism that includes that (like, say, Maxwell’s equations) must necessarily be relativistic, whether you realize it or not. But it’s still a pretty good first-order description.

Just to play devil’s advocate for a moment; I think a lot is known about how magnets work. But nothing about why they work.

There are well defined models and mathematics to predict and describe what happens to create, or operate within, a magnetic field. That is all “how”.

But I don’t think there is an explanation for why that happens in the first place, anymore then we know why gravity exists.

There is no magnetic monopole anymore than there is an atomic particle responsible for gravity.

(On the other hand we do have fundemental particles for positive and negative electrical charge, although I suppose you could argue we don’t really know why they are so. Perhaps string theory can explain that.)

Probably someone really knowledgeable will be along to poke holes in that view.

I can’t speak much to magnetic monopoles (they’re theoretically possible, but Chronos will know way more) but there probably is a particle responsible for gravity- the graviton. The graviton is to gravity what the photon is to light. (Another thing Chronos knows way more about.)

IIRC, and Wikipedia seems to confirm, magnetism is a result of the spin and of moving electrical charges. (And moving magnetic fields likewise an electric charge which is how power is generated.) The best explanation of spin I’ve read was in A Brief History of Time, but the gist is that its a property of elementary particles kinda like charge. Electrons, forex, have a spin of 1/2, while a photon has a spin of 1.

As for the origin of electric charges, quarks carry fractions of a charge that, when added together, equal -1 for an electron or +1 for a proton. More than that I can’t say, other than charge is just a fundamental property of matter.

The photon is responsible for electromagnetism, in the same sense that the graviton is responsible for gravity. As the name suggests, electromagnetism includes both electricity and magnetism.

Light is an electromagnetic wave, so it’s also essentially correct to say that photons are “particles of light”, but that’s not all they are. It is just as correct to say that photons are carriers of electromagnetic force.

One little factoid I stumbled across only recently is that attraction to a (sufficiently small) magnet follows an inverse-cube law! (The basic law is inverse-square distance, but after the north-south cancellation what’s left is inverse-cube distance.)

Has the graviton been shown to exist or it currently just theorized? (Asking from total ignorance on the subject.)

Electrons are not made of quarks. In the standard model, and as far as we have any evidence for, electrons and quarks are both fundamental particles.

:smack:
You’re right, of course. I should’ve taken a look at the handy chart first.

Gee, I wish I’d asked if there was a nonrelativistic version of WHY it works, instead of asking the dumb question I did!

This is the case for dipole fields in general: You get the same sort of falloff for electric dipoles (and would get it for gravitational dipoles, too, if there were such a thing). The only real difference between electricity and magnetism in this regard is that electric monopoles are so common that we don’t worry about the dipole so much, but magnetic monopoles are extremely rare (as my advisor used to put it, “We know magnetic monopoles exist, but there might be a small number of them, like zero”).

Gravitons have never been directly detected, but everyone’s pretty confident that they exist, and of a few of their properties. Details on how they interact with each other and with other particles are still extremely sketchy, though.

Oh, and as for the “why” question, anyone who’s ever spent time with a three-year-old knows that you can’t answer that question for anything. Whenever you think you’ve come up with an explanation for anything, the three-year-old can always just ask why that is, in an infinite recursion.

Why is that?

And that is why all ‘why’ questions end up in a discussion of quantom mechanics.
Why do I have to eat brussel sprouts?