Researchers Discover "Magnetic Current" 249
fsouto writes "Researchers have discovered a magnetic equivalent to electricity. From the article, 'The phenomenon, dubbed "magnetricity," could be used in magnetic storage or in computing. Magnetic monopoles were first predicted to exist over a century ago, as a perfect analogue to electric charges. Although there are protons and electrons with net positive and negative electric charges, there were no particles in existence which carry magnetic charges. Rather, every magnet has a "north" and "south" pole.'"
Bad summary (Score:5, Informative)
The only thing new here is the current, not the "magnetic charge" from the monopole. And it's theoretical physics ridiculously far from being used in magnetic storage or computing.
Article Abstract (Score:5, Informative)
Abstract from the actual paper [nature.com]:
"Electrically charged particles, such as the electron, are ubiquitous. In contrast, no elementary particles with a net magnetic charge have ever been observed, despite intensive and prolonged searches (see ref. 1 for example). We pursue an alternative strategy, namely that of realizing them not as elementary but rather as emergent particles—that is, as manifestations of the correlations present in a strongly interacting many-body system. The most prominent examples of emergent quasiparticles are the ones with fractional electric charge e/3 in quantum Hall physics. Here we propose that magnetic monopoles emerge in a class of exotic magnets known collectively as spin ice: the dipole moment of the underlying electronic degrees of freedom fractionalises into monopoles. This would account for a mysterious phase transition observed experimentally in spin ice in a magnetic field, which is a liquid–gas transition of the magnetic monopoles. These monopoles can also be detected by other means, for example, in an experiment modelled after the Stanford magnetic monopole search."
Re:aren't the 2 linked? (Score:4, Informative)
Nope. Gauss's law [wikipedia.org] (electricity) has some nice formula while the corresponding Gauss's law for magnetism has a big fat zero.
If magnetic monopoles were taken into account, the magnetism one will have a nontrivial div like the electricity one.
Thank you wikipedia. Now I know to ask for for christmas: A Student's Guide to Maxwell's Equations! The amazon reviews are good. Let's learn together, slashdot. div grad curl too, in case old Maxwell's a little heavy with the vector calc
Re:Bad summary (Score:4, Informative)
That's because the summary is just copypasta of the first paragraph of TFA, which goes on to say that monopole "quasti-particles" had already been observed.
Re:"Discovered" magnetic current? (Score:4, Informative)
Re:Article Abstract (Score:5, Informative)
Um. I think that's the wrong article. Look at the date: it's published in 2008; that's hardly news.
Here's the correct one [nature.com] published ... um, on 15th—probably in U.K., since it's still 14th here.
Re:Maxwell Equations (Score:4, Informative)
Maxwell's equations don't preclude magnetic monopoles
False. As you find them in a standard text book, they do exactly that. Div B = 0 [wikipedia.org] means no magnetic monopoles. That said, the standard equations can be easily modified [wikipedia.org] to accomodate magnetic monopoles (a few books do this -- Classical Electrodynamics by Julian Schwinger might be one).
ttp://en.wikipedia.org/wiki/Magnetic_monopole#Dirac.27s_quantization
Re:Maxwell Equations (Score:3, Informative)
I think the point the GP was making was that there was no reason that they couldn't exist...
Exactly. It isn't necessary that they exist, but there's no reason they could not exist and it makes a lot of sense for them to exist for various reasons (charge quantization and symmetry between aspects of the same force being big reasons). But we've never observed them, hence the equations as stated do not account for them. Observe one, and you can trivially modify the equations to account for the fact. The theory is pre-built to accept them. Hence they're not "crying".
Re:Maxwell Equations (Score:2, Informative)
The reason you don't see Maxwell's Equations with magnetic charge in textbooks is because it's pointless to leave them in unless you're specifically looking at the problem of "how would X change if magnetic charge existed?". I happen to have a textbook that assumes magnetic charge throughout the entirety of the text (Balanis, Advanced Engineering Electromagnetics) It doesn't mean that the equations preclude it. Heck, in antenna analysis we model antennas using magnetic current/charge.
Precludes vs assumes (Score:3, Informative)
Okay, I'm replying to myself as I thought I should immediately after posting the above.
Yes, Gauss's Law of Magnetism, one of Maxwell's Equations, says the magnetic field has zero divergence, meaning there is no net magnetic charge.
That is an assumption based on the lack of experimental evidence for a monopoles.
This does not mean Maxwell's Equations preclude the existence of monopoles, because they don't. What's the difference between precluding their existence, and presuming their non-existence? Well, let's look at something that is both assumed and precluded by theory: the speed of light being different for different inertial observers, and Special Relativity.
Special Relativity assumes c is constant for all inertial observers. It also precludes the possibility of that not being true, because the entire theory is based on that assumption, and falls apart if that assumption does not hold. All the equations of special relativity contradict observer-relative speed of light. If you ever discovered a case where this was not true, you would have to scrap Relativity and re-write the theory from scratch. That's precluding.
Maxwell's Equations assume net magnetic charge is zero, but if that assumption doesn't hold, then you simply have another term in the equations and you don't need to go back to the drawing board. Gauss' Law of Magnetism simply becomes a special case where net magnetic charge is zero (though this 'special' case is the most common case). You don't need to re-write the theory of electromagnetism. These researchers are not claiming to be re-writing the theory of electromagnetism, because the theory does not preclude magnetic monopoles.
Re:Maxwell Equations (Score:4, Informative)
Making the equations "symmetrical" for both electric and magnetic charges does not make them any more elegant or powerful
Discussion of the existence of monopoles or true magneto current -- seriously, people -- this sentence is glaringly false. In fact, the use of magnetic charge and magneto have been integral* to electromagnetic analysis for more than 50 years now. Using the symmetric form of Maxwell's equations. The fields created by all sources and media inside an arbitrary closed surface can be analogously modeled as charge and current distributions over the surface. This is what allows you to equivalently model the open end of a driven waveguide as a rectangular patch of magneto current, an electric dipole antenna as a "cigar band" of magneto current wrapping around the feed gap. All of which, I should add, makes the equations much easier to solve. Hell if nothing else the addition of a magnetic boundary conditions can allow numeric models to converge much more quickly.
Arguing that the phenomenon discovered does not truly uncover a magnetic monopole is one thing. Arguing that there is no benefit to symmetrical equations is as silly as that there is no benefit to expressing the equations in the "bastardly" phasor vector notation when a simple set of 12 differential equations of 12 variables would suffice.
*No pun intended.
Re:Maxwell Equations (Score:4, Informative)
What, you haven't encountered the idea before? It's been around a while. Look here. [wikipedia.org]
magnetic flux vs magnetic current (Score:4, Informative)
Well, in the interest of closing the loop, these aren't totally disjoint ideas ;^)
In the standard magnetic circuit with flux and field, the analogy between a magnetic circuit and an electrial circuit is
MMF = PATHINTEGRAL (H dot dl) vs EMF = PATHINTEGRAL(E dot dl)
Without any magnetic monopoles, this path integral that represents the magnetic circuit is merely analogous to a magnetic charge making a loop in the circuit creating a potential around the loop. Although this MMF is now taught as being generated by transformer/inductor coils wrapped around the magnetic circuit using the relationship MMF = N*i, but instead in a world with magnetic monopole current (i.e., magnetic current), in principle the same MMF relationships can be used.
Interestingly with magnetic monopoles this can also be extended like "electrical" circuit element.
R = dv/di, C = dq/dv, L = dF/di, M = dF/dq, i = dq/dt, and v = dF/dt
Historicall, only Resistance ~ Reluctance was the only one of the analogs that made sense w/o magnetic monopoles.
Now that we have magnetic monopoles, the other electrical circuit elements now have possible analogs in a magnetic circuit.
So this is actually a similar idea that shouldn't be dismissed out of hand.
Re:Maxwell Equations (Score:4, Informative)
You just failed physics. Congratulations.
There is no such thing as negative energy (without negative mass anyway).
What you're confusing with negative energy is relative energy--an object can be said to have negative potential energy if it has less potential energy than the arbitrary zero level. This is not the same thing as negative energy (any more than being in debt is having negative dollars, or being below 0 degrees Farenheit is having negative thermal energy).
Re:So what do the field lines look like? (Score:4, Informative)
Yep. Same as like a static electric charge.
Re:Bad summary (Score:4, Informative)
The only thing new here is the current, not the "magnetic charge" from the monopole. And it's theoretical physics ridiculously far from being used in magnetic storage or computing.
The monopole is at most a month old, so it's not like we're talking particularly old news. At worst it's an update on ongoing research.
Re:Maxwell Equations (Score:5, Informative)
There was also no theoretical reason for monopoles _to_ exist. If charge exists, and moving electric charges create magnetic fields, who do you _need_ magnetic charges? Making the equations "symmetrical" for both electric and magnetic charges does not make them any more elegant or powerful, any more than not having "negative mass" makes Newton's equations any less valid.
"Discrete units of net magnetic charge" may be a quantum effect of aligned, moving electrical charges. I still see no need for monopoles.
If you have an analysis of Maxwell that explains the quantization of electrical charge without requiring the magnetic equivalent, you should show it to people. Dirac couldn't do it, so if you have it'd be well received. Not only did Dirac's equations require them, he predicted the magnetic charge quanta to be 68.5 times the electrical charge quanta. Proving Dirac wrong would have enormous consequences, since the 1983 theory of electroweak unification required them to exist and have the predicted charge magnitude, and the W+, W- and Z(0) intermediate vector bosons it predicted (based on the theory that required monopoles) have been detected. Not only that, they have precisely the charge magnitude predicted by the theory based on the predicted magnetic charge magnitude. And if you can show where Dirac went wrong, you can also show where t'Hooft and Polyakov went wrong, since they independently not only showed that any such unification theory required them, but also came to the same prediction of magnitude of magnetic charge as Dirac. Three independent theoretical analyses that make specific predictions which have been tested and shown to be correct would seem to be a tough nut to crack. But if you can show where these were all wrong, it'd be worth a Nobel, just as Weinberg, Salam, and Glashow shared one for the electroweak unification predictions that testing had subsequently and apparently mistakenly supported with data. In fact, if you can point to where Dirac et al. were wrong, you could save a lot of people a lot of money, since the search for the Higgs boson is based on symmetry breaking that requires the monopoles to exist and have a specific charge. If you could just point out where Dirac went wrong, say on the page at http://encyclopedia2.thefreedictionary.com/Magnetic+monopoles [thefreedictionary.com] then we can call CERN and tell them to recalibrate the LHC because they followed Dirac's mistake when they built it. Or should they just trash it? It must really be hosed if it's based on a theory that predicts things, some of which have been detected exactly where they were supposed to be.
Oh, and while you're taking a balanced equation and unbalancing it, the answer to your other question is on that page too. An electrical charge in motion creates a closed magnetic field, so a magnetic charge in motion creates a closed electrical field. You may feel free to not see a need for it either, but by now it should be clear why you don't see these things as necessary. This latter result would seem at second look to be dismissable since it predicts an essentially perpetual motion. However, the perpetual motion machine it describes is available for examination in every electron orbiting every nucleus. This closed electrical current has been detected at a classical scale as a persistent flow such as a superconducting current, in a normal resistive metal ring. This was announced in Science magazine a week ago and mentioned in http://hardware.slashdot.org/article.pl?sid=09/10/10/1338210 [slashdot.org]
Actually it is understandable that some people don;t see the "need" for monopoles any more than they see the need for scalar waves. This is because it has become common to teach the essentials of Maxwell's equations by arbitrarily ignoring some aspects. this is done by setting some of the necessary variables to zero. While this allows one to examine the isolated na
Re:Bad summary (Score:4, Informative)
Ok: Wake up!
There are lots of electrons without protons. For example those which are created together with positrons.
But more to the point, what the OP asked for was not a north magnetic monopole where no south magnetic monopole is anywhere in the universe. What he is asking for is a north monopole where the south monopole is at a completely different place (especially not inside the same crystal as the north monopole).
Example: If you put an electric field on a metal, the electrons will gather on one side. If you now cut the metal in two pieces, where the cut is perpendicular to the electric field, you'll have a positively charged metal part and a negatively charged metal part (note that the electrons never left the metal during that procedure). You can now switch off your field and put both materials in different places; and the positive metal part will not have a negative pole, and the negative metal part will not have a positive pole, that is, both will be monopoles.
So now do the same with those spin crystals. If it works the same (i.e. if you get a north crystal and a south crystal after dividing), then you have real monopoles. However, if both parts exhibit a north and a south pole, you really have dipoles which are arranged so that they locally look like monopoles.
Re:Maxwell Equations (Score:3, Informative)
Re:the article itself, and available (Score:3, Informative)
What are you talking about?
Probably something like this, for the first complaint:
roystgnr@mycroft:~$ wget http://arxiv.org/abs/0907.0956 [arxiv.org]
--2009-10-15 08:39:22-- http://arxiv.org/abs/0907.0956 [arxiv.org]
Resolving arxiv.org... 128.84.158.114
Connecting to arxiv.org|128.84.158.114|:80... connected.
HTTP request sent, awaiting response... 403 Forbidden
2009-10-15 08:39:23 ERROR 403: Forbidden.
roystgnr@mycroft:~$ wget --user-agent="Mozilla/5.0 (X11; U; Linux i686; pl-PL; rv:1.9.0.2) Gecko/20121223 Ubuntu/9.25 (jaunty) Firefox/3.8" http://arxiv.org/abs/0907.0956 [arxiv.org]
--2009-10-15 08:42:20-- http://arxiv.org/abs/0907.0956 [arxiv.org]
Resolving arxiv.org... 128.84.158.114
Connecting to arxiv.org|128.84.158.114|:80... connected.
HTTP request sent, awaiting response... 200 OK
Denying access to web browsers that don't hand you a UserAgent header matching some pattern is a kind of dickish thing to do. Pointless, too. Anyone who wants to crawl your site with a robot and knows to tell it to ignore robots.txt will also know how to use a fake UserAgent. So the only people you're going to deny access to are those people who are using web browsers that you forgot to add to your whitelist.
I'm not entirely sure what the "mangles the file extension info" complaint is about, though. Maybe it's that arxiv, although returning the right MIME type, doesn't return a file with a .pdf extension for the PDF article? This is less upsetting. It's fine to use a browser/OS that isn't popular enough to make someone's whitelist, but everybody should at least use one that can handle long-established HTTP standards.
It's really more of a mathematical construct (Score:3, Informative)