Magnetic Monopolies

Discussion in 'Physics' started by Dave, Jul 3, 2009.

  1. Dave

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    Following a recent walk in the glorious Lake District fells, I stopped in a walkers pub for a quiet post-walk beer (obviously!). On the reading table were recent copies of the New Scientist magazine, not what I expected, but a pleasant surprise.

    An article that caught my eye was on the magnetic monopolies: http://www.newscientist.com/article/mg20227071.100-hunting-the-mysterious-monopole.html

    Interesting reading so I thought I'd share.

    Dave
     
  2. jpanhalt

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    It is interesting. Thanks for sharing and welcome back. John
     
  3. Dave

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    No problem John, and thanks.

    Dave
     
  4. studiot

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    Thanks Dave, but I found it difficult to distinguish real physics from populist fluff.

    Oh well I suppose even 'populist science' authors have to earn their crust.

    From what I could make out, he is suggesting that we could use pretend monopoles to explain certain magnetic phenomema in solids the same way we use pretend charge carriers called holes to explain certain electric phenomena in solids, because it makes the maths easier.

    But like holes, it is only a model.
     
  5. Wendy

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    Still, being able to generate the effect of a monopole is significant. Reminds me of electromagnitism, with that comes real magnets. One of the staples of scifi is the abilitiy to turn monopoles on/off, perhaps this is the first step in that direction.
     
  6. steveb

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    I wish my old electromagnetics professor were alive to see this. He loved the idea of magnetic monopoles and insisted they would be found in some form.

    I wonder, is this sufficient evidence to modify Maxwell's Equations? Yes, it seems to be a quantum effect, but we still sometimes use classical EM theory in quantum mechanical problems. If this truly is a magnetic monopole, then it should be measurable at the macroscopic level by applying Gauss's Law for magnetic fields. We should see that  \int\int B \cdot dS is no longer equal to zero, when applied over a closed surface that contains this medium. Or, maybe they are like hole/electron pairs, there will be a north/south monopole pair drifting and the net effect is zero outside. I suspect the latter case is the situation, but if we start to make devices with this material, we need to model the interior fields and may need a modified form of one of Maxwell's equations. That would be a very significant event to see in our lives.
     
    Last edited: Jul 3, 2009
  7. beenthere

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    A magnetic monopole could not have what we recognize as a "magnetic field", as part of its definition is that a magnetic field forms a closed surface.

    Would that sort of force monopoles to be strongly attracted to any/all oppositely poled (can't really say charged in this case) monopoles? Could an isolated monopole really be said to have a field? How would you detect one?

    It would almost seem as if there should be some level of small scale where disassembly of a magnet should reach the quantum level at which the fragment had to be a monopole. I do not believe the nature of the mechanism of magnetism is any better understood than that of gravity. Can't have a universe without 'em, but what are they, really?
     
  8. Wendy

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    I won't swear to this, but I believe they were looking for a distinct signature of a monopole going through a coil in one of the numerous experiments. I think it was supposed to be a haverwave, a DC wave almost like half of a sine wave. Anybody confirm this?
     
  9. boriz

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    I think I’ve seen monopoles. I think most of us have.

    You have seen the movies of the surface of the sun? With all those lovely twisted magnetic field lines? And occasionally one of them snaps releasing loads of plasma (coronal mass ejection)?

    Well surely, for a moment after the snap, there must be a monopole?
     
  10. beenthere

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  11. Wendy

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  12. AlexR

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    I'm must say that I'm somewhat more than underwhelmed. No doubt I'm missing some important point but it seems to me very much like burying one end of a piece of string in the sand and then claiming that you have discovered the existence of a string with only one end.
     
  13. Kermit2

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    It will turn out to be like quantum mechanics, in that the theory itself may not be how things 'actually' work, but if it gives accurate predictions then it will be useful despite not being a 'true' representation of reality.
     
  14. Wendy

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    Depends how long that string is. If it is several miles long it will allow some interesting experiments, the key being there are no flux lines between the two particles. I've always thought they would be independent, but reality doesn't have to match our vision.

    It will be interesting what devices come out of this.
     
  15. steveb

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    This is definitely an interesting development and I also can't wait to see what practical applications come out of this. Wow, room temperature demonstration of the effect has been discovered so quickly!

    I do think it's important to point out that these monopoles are not real verification of the sought after Dirac magnetic monopoles, and they should be called "psuedo-monopoles" or "monopole-like effects in materials". The scientist that are interviewed try to say this in the most subtle way possible, for obvious reasons. They do say it, but it can be easily missed if you are not tuned into this important difference.

    To understand the importance of the distinction, we can draw an analogy with the "hole" observed in a semiconductor when an exciton separates into a hole-electron pair. The hole-electron pair is a quantum mechanical manefestation in semiconductors in which entities which have a negative charge (the psuedo-electron) and a positive charge (the hole) appear to behave like real charged particle. The distiction is important because the observation of holes in semiconductors would not be proof that positrons exist. However, we know that positrons do exist, as they have been observed in experiments independently.

    Here we are seeing a similar effect. A north-south pole appears to separate and move and each pole takes on particle like properties within a material. This is far from comfirmation that real magnetic monopoles exist.

    If real monopoles are ever found, it will be a very big deal in the physics world. It will be interesting to see if these new materials become a big deal in the engineering world. With such a fast demonstration of room temperature effects, I can't help but feel optimistic about this possiblity.

    We need to do some research on this. Exactly how to we modify and apply Maxwell's equations in this material, or is there no need to modify at all? Are these monopoles sources of flux with no return, similar to an electrical charge? If so, this discovery becomes astonishing, in my view. If I put a closed surface around one of these monopoles, will the integrated flux be non-zero, in violation of Gauss's law for magnetic flux? If we are destined to be doing engineering with these materials and effects, these would seem to be very important questions to answer. The required modifation of any of Maxwell's Laws, even in a very restricted application, would be a remarkable thing.
     
  16. jpanhalt

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  17. Wendy

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  18. jfrost

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    I always found it interesting that the magnetic field can be shown to arise from the special relativistic effects of the relative motion between charges and observers (and/or test charges). Richard Feynman has an excellent analysis of this in Vol 2 of his Feynman Lectures in Physics. You can get the gist from this Wikipedia article, Relativistic Electromagnetism. Scroll down to the section titled "The origin of magnetic forces".

    Force on a positive test charge near charges in motion (current) can be described by either the current's associated classical magnetic field OR, equivalently, by the charges' electric field itself that results from modified charge densities of the current flow (and thus the resulting "modified" electric field and force on the test charge). The modified charge densities arise from relativistic length contraction of the charge current owing to the relative motion between those charges and the positive test charge's reference frame.
     
  19. Wendy

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    So what does this have to do with monopoles?
     
  20. jfrost

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    It just seems strange and marvelous (to me, anyway) that a static charge gives rise to a dipolar field (the E field), relative to a given frame of reference, but any relative motion of the charge (or change in E field) gives rise to a monopolar field. A static charge can either sink or source the E field, depending on its polarity; a moving charge both sinks and sources the relativistic component - the B field. Strange! Even the direction of the force that the magnetic field exerts on a relatively moving test charge is in an odd direction (perpendicular to both the test charge's velocity and the B field direction). The coupling of the E and B fields and their propagation through spacetime for the case of accelerated relative motion is even weirder.

    I'm not making any grand statements or arguments here with which to contradict anyone about anything. I've just always marveled at the relationship between the magnetic field and relative motion, along with it peculiar characteristics, including its apparent monopolar nature, and assumed you all probably do as well. That's all.
     
    Last edited: Jan 5, 2011
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