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Author Topic: Monopoles  (Read 6697 times)

Offline Murchie85

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« on: 21/08/2010 10:56:07 »
I have done some reading and touched over monopoles in my studies but would like to know more about them (please don't just link a wiki page). Are they possible? I know theoretically they are said to have existed or exist although as I understanding physics this should be impossible as split a magnet on any scale and you will always get two poles. Also why are monopoles associated with extremely high energy?

Thanks in advance

Adam


 

Offline syhprum

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« Reply #1 on: 21/08/2010 11:49:38 »
As a subscriber to this forum I am flattered to learn that in your opinion the wisdom displayed here exceeds that which finds its way to WIKI, although there are many erudite and well inform subscribers here a look at the accumulated knowledge that finds it way to WIKI is always worth while.
« Last Edit: 21/08/2010 11:51:12 by syhprum »
 

Offline Murchie85

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« Reply #2 on: 21/08/2010 13:40:02 »
Syhprum three reasons why I didn't want just a wiki link.
1)The reason for my post was to ask opinions, as well and perhaps start an interesting discussion.
2)At university among the first thing you are told is NOT to trust wiki as a source of reliable information.
3)I already checked it anyway.

« Last Edit: 22/08/2010 09:35:56 by Murchie85 »
 

Offline Farsight

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« Reply #3 on: 21/08/2010 19:09:25 »
There are no magnetic monopoles because it's the electromagnetic field. Bear with me:

Imagine we have a particle such as a negatively-charged electron just sitting there in space. Now imagine that you're another electron, and I've just put you down somewhere near to this first electron. You'd experience a force and you'd move directly away from the first electron. Hence you'd consider yourself to be in an electric field, with field lines like this:



If however I threw you past the first electron, you'd also suffer some rotational motion around what you'd describe as the magnetic field lines. Motion is relative, so I can achieve the same result by throwing the first electron past you. It's even better if I throw a whole series of electrons past you, which starts to look like a "current" of electrons. When these are inside a wire made up of positively charged particles, the electric force nets to zero, and the magnetic force is more apparent:



The magnetic field of a bar magnet is there because the electrons in the iron are moving in a common circular orientation. You get the same kind of field when you wrap that vertical wire into a solenoid.



You can't achieve a monopole by chopping the magnet in half just as you can't achieve a monopole with a shorter solenoid. Keep cutting it down and in extremis you end up with a single particle like an electron, with relative motion, and it has an electromagnetic field, not a magnetic field.

 

Offline JP

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« Reply #4 on: 22/08/2010 03:41:11 »
Farsight's right that chopping up a magnet won't get you a monopole, because the magnetic field of the magnet is made up of tiny electric charges moving around, which are called dipoles.  A monopole would just be a tiny magnetic charge that emits a magnetic field without moving.

There are theories that propose their existence--and they help explain why electric charged come in discrete units rather than taking on any possible value.  As far as I know, they don't require high energy to see.  They should be floating around freely in the universe.  However, all attempts to search for them have come up empty handed. 
 

Offline Soul Surfer

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« Reply #5 on: 22/08/2010 10:14:55 »
Conventional thinking about magnets does not allow the existence of an isolated pole.  However in a medium that consists of lots of tiny bar magnets all linked together and neutralising each other it is possible to get isolated mobile poles in the same sort of way as electrons and "holes" propagate through semiconductors.  if you flip one magnet to create a pair of non neutralised poles successive flips can cause the north and south poles to move around freely.  it is possible to get states like this in conventional materials called anti-ferromagnets  in this case the magnetic domains line up not to create an overall field but to cancel each other out like a pair of bar magnets stuck together.
 

Offline tommya300

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« Reply #6 on: 22/08/2010 12:22:32 »
« Last Edit: 22/08/2010 12:25:32 by tommya300 »
 

Offline Murchie85

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« Reply #7 on: 22/08/2010 19:59:19 »
Farsight, thanks a lot for your diagrams and explanation that has helped me get my head round it a bit. I think I read in the new scientist that monopoles had been discovered but I guess it may just be something analogous to it, does anyone know more?
 

Offline Ron Hughes

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« Reply #8 on: 22/08/2010 21:07:12 »
What is the difference between an electron and a monopole?
 

Offline Soul Surfer

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« Reply #9 on: 22/08/2010 23:42:09 »
Ron  thats a bit like saying what's the difference between a mouse and an elephant.  They are just different.  As well as having a negative charge an electron has spin and is a magnetic dipole i.e. it has a magnetic moment that can be measured that is it has a north and a south pole.  A magnetic monopole if it exists would have only a single pole and probably no charge.  It is highly probable that if they exist, they can only be created in pairs
 

Offline JP

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« Reply #10 on: 23/08/2010 03:56:34 »
I think I read in the new scientist that monopoles had been discovered but I guess it may just be something analogous to it, does anyone know more?

If it's the article I'm thinking of, the researchers created a magnetic dipole, which has a north/south end just like a magnet, and then separated the north and south ends of it by a huge distance, making each end look somewhat like a single pole.  Of course, it's still not a monopole. 
 

Offline imatfaal

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« Reply #11 on: 23/08/2010 18:15:28 »
If someone does discover a simple magnetic monopole then modern physics is in a bit of a quandary - maxwell's equations are based on the fact that you cannot have one.  to be precise it is gauss' un-named law, normally shown as maxwell's second equation, that shows there can be no magnetic monopoles.  formally, it says that the closed surface integral of the mag field over an area vector must be zero; the net magnetic flux through any surface must be zero, ie as many magnetic field lines enter as exit and no magnetic "charge" can accrue. 

and if maxwell were shown to be so fundamentally wrong... well there would be a boom in the text book industry.

Matthew   
 

Offline Ron Hughes

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« Reply #12 on: 23/08/2010 20:30:19 »
soul, in the case of a dipole the fields lines come out of one pole and go back into the opposite pole. In the case of the electron the field lines go into the so called point particle. I don't know from where they originate.
 

Offline Soul Surfer

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« Reply #13 on: 23/08/2010 23:53:40 »
The electron behaves just like any bar magnet.  look up  http://en.wikipedia.org/wiki/Electron_magnetic_dipole_moment for a detailed explanation.  it is in effect a rotating electrical charge.  While it is true that at very high energies electrons behave as point particles this is because their wavelength get very short.  At normal energy levels an electron is quite a large thing and defines the size of atoms by its wavelength.
 

Offline Ron Hughes

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« Reply #14 on: 24/08/2010 00:01:02 »
So your saying that the drawings farsight posted are wrong?
 

Offline JP

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« Reply #15 on: 24/08/2010 02:16:56 »
If someone does discover a simple magnetic monopole then modern physics is in a bit of a quandary - maxwell's equations are based on the fact that you cannot have one.  to be precise it is gauss' un-named law, normally shown as maxwell's second equation, that shows there can be no magnetic monopoles.  formally, it says that the closed surface integral of the mag field over an area vector must be zero; the net magnetic flux through any surface must be zero, ie as many magnetic field lines enter as exit and no magnetic "charge" can accrue. 

and if maxwell were shown to be so fundamentally wrong... well there would be a boom in the text book industry.

Matthew   

Quite true, but I'm not sure if it's a big problem for modern physics.  You'd need to insert a source term in one of Maxwell's laws, and the textbook industry would make a bit of money, but then you'd be able to explain charge quantization in quantum mechanics (plus Maxwell's equations would now be much more symmetric).  I don't think that that one extra term in Maxwell's equations actually cause any major pillars of modern physics to fall.

From what I've heard, I think the strangest part about them is that when we look for them experimentally, they appear to not exist...
 

Offline Atomic-S

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« Reply #16 on: 24/08/2010 05:38:37 »
The existence of magnetic monopoles would have certain consequences:  One, as just pointed out, Maxwell's equations would have to be generalized, by including terms for magnetic "charge" density and magnetic "current"; this is not an extremely radical change. Another: If monopoles exist, what would they be like at the subatomic level? A first speculation would be that they would have the same mass as electrons and positrons, but the electrostatic charge would be zero (and the magnetic "charge" would be 1). Presumably they would also have a spin , which would have certain consequences:  As an electron, due to its spin, developes a magnetic dipole moment, likewise owing to the generalized Maxwell's equations, a magnetic monopole, due to its spin, would have an electric dipole moment.

That leads to some interesting physics:  What would happen when an electron and a magnetic monopole met? The electron would undoubtedly flip around so that it was pointing its most favorable magnetic pole at the monopole, causing attraction. The magnetic particle would do likewise with its electric dipole mement, reinforcing the attraction. The 2 particles would meet. Then what? We know that when an electron meets its opposite (positron), they annihilate in a burst of electromagnetic radiation. When an electron and a mangetic monopole meet, what would we expect? If we could figure out the answer to this question, we might be able to describe the circumstances required to create monopoles (or describe why they are an impossibility).

At the macroscopic level we have further consequences:  If a cloud of monopoles is released near a bar magnet, they will be sucked toward the most favorable pole of the bar magnet, follow the field into the magnet, perhaps travel through it, on out the other side, and around again for another ride -- indefinitely. This would be a good way to generate unlimited power out of nothing, it would appear. Inasmuch as such a result is fairly unlikely, the traveling monopole current would have to have some additional effect. What would it be? 
 

Offline Soul Surfer

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« Reply #17 on: 24/08/2010 22:52:07 »
Ron, Farsight's drawings are perfectly OK and what I said was not incompatible with them the first drawings relate to electrical charges not magnetic fields and the magnetic fields re true fro electrons which have rotational energy as well as electrical charge and this rotational energy (spin) creates a magnetic field from the charge. 
 

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