electromagnetism

[darthbadass]

From whence does the fundamental quantity of "charge" come, ie, why do protons electrons and quarks have specific charges and what gives them their charge? Does it originate from a subatomic field in 4D? And why do moving charges create magnetism? Could the four fundamental forces be unified in higher dimensions? (Do they originate from 4D or 5D?)

[houserichichi]

The electron has charge of -1 by convention. The proton has charge of +1 by convention. As the proton is made up of three quarks they have respective charges of 1/3 (or multiples thereof) by convention. Charge is an intrinsic property of how a particle interacts with the electric field. It's a combination of weak hypercharge and weak isospin.

Re: magnetism...copied directly off physics forums

There are different types of magnetism, lucky for you, the three main being: Diamagnetism, Paramagnets, and Ferromagnetism. We'll go backwards.

Ferromagnetism is the kind you normally observe. Refrigerator magnets, speaker magnets, wallet magnets, permanent magnets.

Ferromagnetism is due to the direct influence of two quantum effects: quantum spin, and the Pauli exclusion principle.
The spin of an electron, (something you can't visualize correctly) combined with its orbital angular momentum, results in a magnetic dipole moment and creates a magnetic field. (if you need to, you can imagine the electrons spinning around). The dipoles tend to align spontaneously, without any applied field.

Ferromagnetism manifests itself in the fact that a small externally imposed magnetic field, say from a solenoid, can cause the magnetic domains to line up with each other and the material is said to be magnetized. The driving magnetic field will then be increased by a large factor which is usually expressed as a relative permeability for the material. Ferromagnets will stay magnetized after having been aligned to this exterior magnetic field. Called hysteresis. The fraction of the saturation magnetization which is retained when the driving field is removed is called the remanence of the material.

All ferromagnets have a maximum temperature where the ferromagnetic property disappears as a result of thermal agitation -- the Curie temperature. You know that heat is actually just the atoms shaking around, after the atoms shake around enough they aren't all aligned the same way!

So really, all the electrons are "spinning" the same way, and that creates the field.

Diamagnetism is a very weak form of magnetism, that needs another magnetic field to work. It is the result of changes in the orbital motion of electrons. Diamagnetism is repelling. Diamagnetism is found in all materials; however, because it is so weak it can only be observed in materials that do not exhibit other forms of magnetism. Some diamagnetic materials that should be recognized are water, pyrolitic graphite, and superconductors.

Paramagnetism is closely related to diamagnetism, and also needs an external magnetic field. It occurs temporarily, when its magnetic dipoles align with the external field. Some paramagnetic materials that should be known are oxygen, aluminum, and sodium.

Re: unification...maybe. The string theorists certainly believe it to be so.

[bo198214]

And why do moving charges create magnetism?

Short answer: It is simply a relativistic effect.
Eintein presented this already in 1905 in his paper On the electrodynamics of moving bodies.
For an introduction see Schroeder: Purcell simplified.
You can also try to follow our discussions about magnetism in higher dimensions 4D Magnetism Solution.

[Keiji]

Something I was wondering:

Protons are 3x +1/3 quarks, so they have a +1 charge.
Neutrons are 2x +1/3 quarks and a -2/3 quark, so they have a 0 charge.
Electrons are a +1/3 quark and 2x -2/3 quarks, so they have a -1 charge.

What happens if there is a particle with 3x -2/3 quarks? Is this even possible?

[houserichichi]

A couple of baryons with charge +2 (that is, they are made up of three quarks with a combined charge of +2) are the Delta++ and the Sigma++ charm. The Phi-- is an "exotic baryon" consisting of two stranges, two downs, and an anti-up quark for a combined charge of -2. It and two of its other makeups are listed in the Review of Particle Physics with some hesitation and they've apparently been seen by six independent experimenters. I've no speculation on pentaquarks.