# How to make a monopole magnet?

I want to create a monopole magnet. Is this practically / theoretically possible?

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– Emilio Pisanty Aug 14 '12 at 4:09
thanks for the advice! – Pranit Bauva Aug 17 '12 at 13:22
– user12345 Apr 12 at 11:08

## 6 Answers

As Mark M says in his answer,you cannot have a monopole magnet.

You can simulate one. After all when you are at the north pole of earth, to all intents and purposes that is a monopole for magnets in the area.

By spreading the magentic lines of one of the poles on a large area and concentrating the other to a very small one.

Look at the images here. If you take a bunch of long supple permanent magnets and open one side to a large area, effectively you will have one strong pole in the small area. If you make an electromagnet, make the turns wider and wider on one side so that the field is dispersed in a large area.

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Magnetic monopoles can be created according to numerous Grand Unified Theories (GUT). The idea is that at sufficiently high energies you can reach an energy range where three of the four fundamental forces (strong nuclear, weak nuclear, and electromagnetism) couple to one another and are the same force. Such a state existed in the universe a tiny fraction of a second after the Big Bang. As the universe cools, the universe undergoes a phase transition where a this highly symmetric state is lost (Symmetry breaking). Depending on the topology of the group defining GUT, this can result in a number of different types of cosmic defects, such as cosmic strings, domain walls, textures, and... magnetic monopoles! The framework to understand their creation is often called the "Kibble Mechanism", where the essential idea is different parts of the universe undergo the phase transition at slightly different times and the topological defects emerge based on which symmetry breaks (discrete, cylindrical, etc). In the case of magnetic monopoles, one needs to break spherical symmetry.

Sounds so easy right? Just break some spherical symmetry and you get your monopoles... Except that in order to create this highly symmetric state, you need absurdly large amounts of energy (and probably in some non-traditional geometry) that it is probably firmly out of the range of any current experiments or cosmic processes (it is estimated that the a magnetic monopole would have a mass of about $10^{15}$ GeV, compared to LHC's $10^3$ GeV range). Also it could be the Universe admits a particular GUT that doesn't have the correct symmetries so that, when it is broken to the standard model, it won't create monopoles. However, this hasn't stopped a team from trying at the LHC to try and create some monopoles.

In every-day energy ranges, magnetic monopole production is impossible due to the divergent less property of magnetic fields.

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"magnetic monopole production is impossible due to the divergent less property of magnetic fields." ... You have to explain why, because this property is a priori empirical. – Chris Gerig Aug 14 '12 at 18:38

No, it isn't possible. Gauss' Law for magnetism states that $$\nabla \cdot B = 0$$ This means that the divergence of the magnetic field is zero - which translates into the fact that there are no magnetic charges, that both poles are equal. So, no magnetic monopoles. Or at least, none that would be available for you to build. The issue is a bit more complicated in QFT.

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Remark: This is only true if there are no actual monopoles in the vicinity. – Chris Gerig Aug 14 '12 at 5:12

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The zero in Gauss's law is empirical. It's in there because we haven't see any magnetic monopoles, but it is not required to be that way by more fundamental physics, and you can't use it to justify the non-existance of the things. – dmckee♦ Jan 8 at 22:37

Actually, I'm not sure we can rule such things out! The divergenceless property of the magnetic field is empirical, because we haven't seen any monopoles.

That being said, it is at least practically impossible, because of edge effects of the material which destroy any true radial field lines.

The true reasoning for this to be "theoretically impossible". If there are no physical source monopoles in the vicinity, then any configuration will be made up of dipoles (or possible higher-order multipoles). But any collection of dipoles cannot mathematically equal a monopole.

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what do you mean by "edge effects"? And yes, it should be specially emphasized that you can't construct a true monopole from dipoles, that's what OP probably meant. That is without some kind of new elementary particles it is impossible. – Yrogirg Aug 14 '12 at 7:55
"BUT it does NOT say you cannot build your own configuration!" It does say that you can't build your own. You either find magnetic monopoles or you are stuck with induced dipoles. Those are your only choices. – dmckee♦ Aug 14 '12 at 16:50
No that was before my update. The point is, people simply say "it can't happen because $\triangledown\cdot B=0$", but some further explanation is required... that condition is definitely violated when monopoles are in the area, but when they aren't, WHY can't it be simulated? And the reason is that dipoles cannot represent monopoles mathematically. – Chris Gerig Aug 14 '12 at 17:35

Practically at the present

Maxwell's equations of electromagnetism relate the electric and magnetic fields to each other and to the motions of electric charges. The standard equations provide for electric charges, but they posit no magnetic charges. Except for this difference, the equations are symmetric under the interchange of the electric and magnetic fields. Symmetric Maxwell's equations can be written when all charges (and hence electric currents) are zero, and this is how the electromagnetic wave equation is derived. Fully symmetric Maxwell's equations can also be written if one allows for the possibility of "magnetic charges" analogous to electric charges. With the inclusion of a variable for the density of these magnetic charges, say $ρ_m$, there will also be a "magnetic current density" variable in the equations, $j_m$. If magnetic charges do not exist - or if they do exist but are not present in a region of space - then the new terms in Maxwell's equations are all zero, and the extended equations reduce to the conventional equations of electromagnetism such as ∇•B = 0 (where ∇• is divergence and B is the magnetic B field). At the moment, magnetic monopoles cannot be created.

Theoretically and perhaps futuristically

However, when thinking theoretically it is slightly different. When you take into account Grand Unified Theories (GUT), magnetic monopoles can be predicted. At energies that are currently not possible to reach, you can reach a point where the strong force, weak force and electromagnetism combine to become essentially the same force. The GUT can, in theory, result in magnetic monopoles, so long as spherical symmetry is broken. I call this "futuristically" because it will be a hell of a long time before we can reach energy levels necessary (roughly 10^16 GeV)

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See these publications of the discovery of monopoles. The first two were published in Science:

Morris, J. et al. Science advanced online publication doi:10.1126/science.1178868 (2009).

Fennell, T. et al. Science advance online publication doi:10.1126/science.1177582 (2009).

Kadowaki, H. et al. preprint at http://arXiv.org/abs/0908.3568v2 (2009).

Bramwell, S. T. et al. preprint at http://arxiv.org/abs/0907.0956 (2009).

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