Talk:Magnetic monopole

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so?

Hmm... so? Bicycle^wheel 19:06, 12 August 2015 (UTC)

Hmm. Time to go bullshit-hunting? WalkerWalkerWalker 19:58, 13 August 2015 (UTC)

Yeah, there's gotta be woo around this - David Gerard (talk) 23:09, 13 August 2015 (UTC)

There's a lot of magnetism woo.--Arisboch ☞✍☜☞✉☜ 23:11, 13 August 2015 (UTC)

I'm sure there's also creationists out there saying we should reject our whole current cosmological model just because we haven't found any monopoles yet. Later: Yep, pretty much. 141.134.75.236 (talk) 23:32, 13 August 2015 (UTC)

Thanks; that page has found its way before the firing line. WalkerWalkerWalker 21:45, 14 August 2015 (UTC)

I'm definitely not an expert, but

If magnetism is an emergent property resulting from electrons' spin, whence comes the need for monopoles? We don't need phonons, for example, to be actual particles for sound to be a thing. 142.124.55.236 (talk) 20:19, 15 August 2015 (UTC)

I'm not either, but... We have magnetic dipoles in abundance, like electrons, or bigger st00f like bar magnets. Monopoles are just special because (a) they're one pole without other, which seems like it would be a common thing but isn't actually, (b) they would provide an explanation/reason for the observed quantization of electric charge (I will admit that I have yet to wrap my head around some of the wavefunction stuff involved in the reason why) which particles without a net magnetic charge (q_m = 0, making that whole fraction down in the footnotes zero (and thereby an integer) regardless of the values of electric charges) don't, and (c) some particular theories predict their existence, but we haven't found them. If the question is "do we need magnetic monopoles, quasiparticles or not, to have magnetism" then I think the answer is no, we don't, that they're just interesting/an unfulfilled prediction. Was one of those things a quasi-answer? WalkerWalkerWalker 20:29, 15 August 2015 (UTC)

Actually, correct that I think to I'm almost fully certain; from a theory/mathemagics perspective moving electric charges can create a nonzero magnetic field, and of course from the observational angle magnetism seems to be doing just fine without many if any around. WalkerWalkerWalker 20:38, 15 August 2015 (UTC)

Well, an electron's spin automatically gives it both a 'north' and a 'south' pole. If the way particles gain magnetic poles automatically makes them bipoles, why come up with monopoles? Doesn't seem very Occam's Razor-y. And if the spin creates the poles, aren't they trying to quantize that spin? Seems kind of like an odd thing to posit a quantum particle for. 142.124.55.236 (talk) 20:46, 15 August 2015 (UTC)

Okay, so umm let me try with what limited knowledge I have (bear with):

1. Why? Well, the general symmetry/parallelism between electricity and magnetism and their close relationship could be a sorta motivation; after all, we have electric monopoles already; they're such ordinary things we don't even call them that. As for theoretical motivations specific to the predictions in various GUTs, probably something about symmetry breaking of something which is way the hell above my paygrade no clue. Sorry. As for motivations just in general, it seems like they would provide a relatively simple reason for the quantization of electric charge (i.e. why do all particles we know of have charges that are exactly integer multiples of the charge on a down quark (or a third of the electron charge)?), which would other wise be either a pretty grand oddity without explanation or require some other, less simple explanation. TL;DR: I'd argue that Occam's razor favors monopoles, not because they are needed to explain magnetism, but because they somewhat neatly explain why electric charges are limited to integer multiples of a fundamental charge.
2. Spin: Erm... I'm not sure I fully follow the question; I know that spin is quantized anyhow (to half-integer values, if I recall, although I don't know for sure how those values are related to the actual angular momentum resulting). And yes, the spin of a charged particle creates a magnetic dipole, and... I'm going to go look some things up; my memory is getting slippery.

Sorry for the semi-answers. WalkerWalkerWalker 21:27, 15 August 2015 (UTC)

No worries. ;) 142.124.55.236 (talk) 22:27, 15 August 2015 (UTC)

Okay, followup to number two: (a) the thing which takes half-integer values is called the spin quantum number; my previous brushes with it have been in chem classes in the context of how orbitals fill up etc. If we call that value s, then the magnitude of the actual spin angular momentum is $\hbar {\sqrt {s(s+1)}}$ (the math tags have invaded the talkpage also! Mwahahahahahaha!). The spin angular momentum is a vector with x, y, and z components; these can't be determined with much real certainty for a single particle, but for large collections where they're ~aligned an average can be. Apparently that vector is roughly analogous to the role of an axis of rotation in more... classical scenarios. Anywho, that vector is what appears as boldface S down in the footnote about magnetic moment of the electron; note that the magnetic moment is also a vector, which is parallel (in the case of positive charge) or anti-parallel (in the case of negative charge) to the spin angular momentum. And (b) what I went to look up, the relation between magnetic field/flux density/whatever B and magnetic moment μ, is as follows: $\mathbf {B} ={\frac {\mu _{0}}{4\pi }}\left({\frac {3\mathbf {r} ({\boldsymbol {\mu }}\cdot \mathbf {r} )}{|\mathbf {r} |^{5}}}-{\frac {\boldsymbol {\mu }}{|\mathbf {r} |^{3}}}\right)$ (where μ₀ is the vacuum permeability (a constant) and r is a vector representing position relative to the guilty magnetic moment) which has to have some less painful statement. At any rate, nonzero B can be calculated as a result of the magnetic moment of an electron. Back to (c) what I was saying way back, though, spin is already restricted to certain values by... things. I still haven't gotten that sorted out, but I think it relates to the solutions of the Schrodinger equation... Head. Swimming. Send halp. WalkerWalkerWalker 23:23, 15 August 2015 (UTC)

Also, I added a hopefully helpful clarification of what was meant by "sources" of the magnetic field. I had one meaning in mind; everyday English kinda had another. WalkerWalkerWalker 22:19, 15 August 2015 (UTC)