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Researchers Discover "Magnetic Current"
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.'"
If this is a discovery then why did I learn about this in my electromagnetics class I took a semester ago? And why did I have to work on problems with magnetic circuits if this phenomenom wasn't discovered yet?
I think so. It sounds more like "electron holes" in semiconductors. The spin ice contains tetrahedrons formed from ions. Because of this arrangement, adjacent ions must form a positive-negative pair, which then affects the way electrons spin and the resulting magnetic field. Bring in an external magnetic field and that runs the process in the opposite direction. That's where the storage idea comes from.
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No, they aren't. Maxwell's equations don't preclude magnetic monopoles or the movement of net magnetic 'charge' (aka 'current'). In fact it's always been a mystery why monopoles didn't appear to exist. There was no theoretical reason why they shouldn't, we have just never found a particle carrying a net magnetic charge. We still haven't exactly, just a crystal structure in which you can find discreet units of net magnetic charge, but that's effectively the same thing. And now we've seen that these units can move through a structure, so magnetic current exists.
In a way this must be a relief. Electricity and magnetism are symmetric in so many ways, it was odd that in this one way they weren't since they're ultimately aspects of the same force (electromagnetism).
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Basically, what they found was a material that looks like two opposite magnetic monopoles. In other words, they found a magnetic dipole.
Wake me up when I can buy a north magnetic monopole, and not get the south magnetic monopole with it.
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.
Oh quasi-particles; on one hand you you think "well they're just mathematical constructs rather than physical things" but then you realize that regular particles fall into the same category. I heard of an interesting experiment where a Stern-Gerlach experiment was conducted on a dark-state polariton and resulted in the same effect as for nuclei. You can really only talk about how something behaves when a particular measurement is performed when treating it within whichever theory you're using, calling something a particle or a quasi-particle doesn't really matter.
So if this is the future...where's my jet pack?
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Okay, yes, I almost replied to myself to point out that the one equation based on the lack of the observation of magnetic monopoles would change. But none of the rest of the theory would change, and as you point out Maxwell's theory perfectly accommodates this change, so yeah, Maxwell's equations(plural) aren't "crying", except maybe with joy that now the expected symmetry has been discovered.
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No, they aren't. Maxwell's equations don't preclude magnetic monopoles or the movement of net magnetic 'charge' (aka 'current'). In fact it's always been a mystery why monopoles didn't appear to exist. There was no theoretical reason why they shouldn't, .
Yes and no. Its true that if you look at maxwells equations in the traditional form (with div and grad) the statement of no monopoles (Div B) is simply one of empirical observation: monopoles have not been seen.
However if you cast maxwells equations in differential forms it becomes intuitively obvious why there are no magnetic monopoles. electricity is a one form. Magnetism is a two form. Two forms cannot come from monopoles.
That's only an artifact of Maxwell's equations assuming there are no magnetic monopoles. Add them in, and the equations are perfectly symmetrical for electricity and magnetism, the only difference is the name of the variables and the quantities they represent are swapped. Their partial differentials are identical otherwise.
Electricity and magnetism are two aspects of the same force, electromagnetism. They are mediated by the same particle, the photon. The lack of symmetry in this one aspect is theoretically unnecessary, and philosophically kinda weird. That's not proof, of course. Demonstration of net magnetic charges is.
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The law may need to be rewritten, but as written it does say no monopoles.
Which is trivial to do, and doesn't contradict the rest of the theory, and hence they aren't "crying". The possibility of monopoles has been accepted for a very long time. It's simply the lack of experimental observation that ever caused them to be written in the first place. Re-write Maxwell's equations given the existence of 'magnetic charge', set that charge to always be zero, and you get the equations as written.
Maxwell's equations don't preclude the existence of monopoles. They are simply stated in terms that assume there aren't any based on the lack of evidence for them. His theory is fine, his equations are not "crying".
I don't understand why this is so hard to understand. Outside of the fact that you're all just being pedantic. I guess I should have said Maxwell's theory of electromagnetism.
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The classic illustration of magnetic field lines is to put a big bar magnet on a table and sprinkle iron filings on and around it; they will end up tracing the magnetic field lines of the bar magnet.
So say they could construct the monopole equivalent of such a bar magnet, just one big lump of North or South. If we put that on a table and sprinkled iron filings on and around it, what (if any) lines would they end up tracing? Just rays away from the monopole?
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Would they though? Assume a negative mass which still has a positive volume. If you use the (probably way oversimplified) model of positive mass objects acting like a lead ball on a rubber sheet in space you'd wind up with negative mass objects pinching it and pulling it upwards.
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What is a magnetic field composed of? The article says that a small magnetic field is formed around the muons. Is a magnetic field composed of particles?
"If it doesn't agree with experiment, it's wrong" - Feynman
These "local monopoles" described in the experiment are really just super-long dipoles, and though they have interesting properties, they are not separable and not on the scale of fundamental particles.
This is expected because, though perpetual motion of the third (and wimpiest) kind already exists in atoms and in superconductors, real magnetic monopoles would provide perpetual motion of the first (and awesomest) kind, the kind that violates conservation of energy. And not only is conservation of energy an observed fact, it's also a beautiful theoretical result of Noether's Theorem.
So while the symmetry of magnetic monopoles existing is nice and all, I prefer conservation of energy. Sorry Dirac, but you don't mess with Noether.
Instead of a rubber sheet, imagine a thin, infinite sheet made of water*. A normal mass would act like a straw sucking at the water, pulling it inwards more quickly. Anything that entered that region of spacetime would be 'attracted' to the object.
Using this analogy, a negative mass would act like a straw 'blowing' at the water, so anything moving close to it would be repelled.
* Resting on a giant turtle, naturally