# How to make a monopole magnet?

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

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The research-level tag is not appropriate. Please read the tag wiki and the faq - and, for good measure, search wikipedia. – Emilio Pisanty Aug 14 '12 at 4:09
thanks for the advice! – Pranit Bauva Aug 17 '12 at 13:22
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 arXiv.org/abs/0908.3568v2 (2009). Bramwell, S. T. et al. preprint at arxiv.org/abs/0907.0956 (2009). – user23073 Apr 12 '13 at 10:19
Make some spin-ice: en.wikipedia.org/wiki/Spin_ice and references therein. – user12345 Apr 12 '13 at 11:08
In extension to Peto Verum's reply, apparently, there are magnets simultaneously being a monopole as well as being a chiral object... Take a look at Unwinding of a Skyrmion Lattice by Magnetic Monopoles Science 31 May 2013, Vol. 340 no. 6136 pp. 1076-1080, DOI: 10.1126/science.1234657 by P. Milde et al. – Buttonwood Jun 20 '13 at 19:06

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

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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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
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
In the light of new technology this is incorrect. Please see my answer. – user100712 Dec 15 '15 at 8:28

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
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 '13 at 22:37

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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The results were recently published in the journal Nature.

Although predicted over 80 years ago, the fundamentally quantum-mechanical configuration of the monopoles has not previously been observed in any physical system. The reported results demonstrate the structure in an ultracold atomic gas.

"The creation of a synthetic magnetic monopole should provide us with unprecedented insight into aspects of the natural monopole," says Prof. David S. Hall from Amherst College, USA. "It's not every day that you get to poke and prod the analogue of an elusive fundamental particle under highly controlled conditions in the laboratory," he continues.

Evidence for magnetic monopoles has been sought in sources as diverse as lunar samples and ancient micas. The multibillion-euro LHC particle accelerator at CERN has also been used in the search -- but no magnetic monopoles have been convincingly identified. The discovery of the synthetic monopole provides a stronger foundation for these efforts.

"Our achievement opens up amazing avenues for quantum research. It feels incredible to have been a part of such a major breakthrough," says a delighted Dr. Mikko Möttönen from Aalto University, Finland. "Synthesis of the monopole is the starting point for many new breakthroughs in quantum physics research. In the future, we want to get even a more complete correspondence with the natural magnetic monopole," he continues.

A magnetic monopole is a particle just like an electron, but with a magnetic rather than an electric charge. Some 80 years ago Paul A. M. Dirac, one of the founders of quantum physics, discovered a quantum-mechanical structure allowing the existence of magnetic monopoles. Dirac's original framework has now been experimentally realized for the first time.

Video on the monopole creation: http://youtube.com/watch?v=HSDoIf5FY2s

Background

Magnetic monopole

"A magnetic monopole is an isolated magnetic pole, magnetic charge, and a point-like source of magnetic field."

An electron is a point-like particle that carries a so-called elementary electric charge. This means that an electron is an isolated source of an electric field. Can a magnetic field have a similar point-like source?

Every one of us has likely held two bar magnets and noticed that their ends either attract or repel one another. The ends of the magnet are referred to as poles and every magnet has one end that is a north pole and one that is a south pole. A magnetic north pole attracts a magnetic south pole, but repels another north pole. In general, opposite poles attract, and identical poles repel. In this respect, magnetism is very much like electricity, which exhibits the same attractive and repulsive behavior involving positive and negative electric charges.

When a bar magnet breaks, two smaller bar magnets are created, each with its own north and south pole. You can break each of these smaller magnets in two, and so on, and every resulting magnet has a north pole and a south pole. Even at the atomic level, north and south poles always appear together. One cannot produce in this way a solitary pole, or monopole, that acts as a single point source of the magnetic field.

Are there other ways to find magnetic monopoles? As yet, not a single natural magnetic monopole has been verifiably observed. This was initially considered to be a problem, because theoretical models that described the post-Big-Bang period predicted that they should be quite common. However, a special model for the expansion of the universe was developed that can explain the extreme rarity of these particles.

According to some theories, the energy content (mass) of a single magnetic monopole is so large that if it were completely used to recharge the battery of an electric car, this vehicle would be able to travel for kilometres with the energy. This explains why magnetic monopoles are probably not likely to occur in a particle accelerator. If the mass of a magnetic monopole really is that large, the energy released from the collision of a negatively and positively charged monopole would be as much as the energy released in the explosion of a kilogram of dynamite!

Dirac monopole

"A Dirac monopole is a point-like source of a possibly artificial magnetic field that forms at the endpoint of a quantum whirlpool."

In quantum mechanics, an electron is described by a diffuse wave-like object rather than a point-like particle. Paul Dirac was the first person to understand the importance of studying the end points of quantum-mechanical whirlpools within these electron waves. He noticed that when an electron has such a terminating vortex, a magnetic monopole inevitably forms at the end point. A terminating vortex is the defining characteristic of the Dirac monopole.

Dirac also noticed that if the universe contains even a single magnetic monopole, it specifies the smallest possible value for an electric charge. All observed charges must be integer multiples of this minimum value; in other words, charge must be quantized. The existence of a monopole would therefore explain the experimental observation that electric charge is quantized.

Dirac monopoles are generally analyzed in a fairly simple quantum-mechanical model. Magnetic monopoles have since been studied in more general, so-called unified field theories, in which they could exist in the absence of a terminating vortex.

Synthetic magnetic field

"A synthetic magnetic field is an artificial field that leads to particle dynamics equivalent to those of an electric charge in a corresponding natural magnetic field."

Electrons are not the only physical systems that can exhibit terminating vortices. Thus a Dirac monopole can also appear in other systems, such as the Bose-Einstein condensate. Rather than being related to the natural magnetic field, this monopole can be associated with a synthetic magnetic field. Importantly, the structure of the monopole is identical to that of a Dirac magnetic monopole. This is why the Dirac monopole observed in the synthetic magnetic field is closer to a natural magnetic monopole than any earlier observation.

Spin

"Roughly speaking, spin indicates how fast a particle is spinning around its own axis and the orientation of that axis."

Spin is a magnetic property of many particles, including electrons, protons, neutrons, and even many types of atoms. For example, the electron spin is composed of two basis states: up or down. This describes whether the electron is spinning around its axis in a clockwise or counter-clockwise direction.

A particle with a non-zero spin creates a magnetic field around it. However, this is not a monopole field -- it is a so-called dipole field with both north and south magnetic poles, just like a bar magnet. Even this smallest of bar magnets cannot be broken into two separate magnetic monopoles.

In fact, bar magnets are composed of countless numbers of small spin dipoles, nearly all of which point in the same direction. Overlapping poles of different sign cancel out the field of each other, and thus the field of an ideal bar magnet looks as if it has magnetic poles only at its ends.

Spins tend to align along an externally applied magnetic field, which is the key to the creation of the synthetic magnetic monopole.

Synthesis of a monopole

"A monopole is created in a Bose-Einstein condensate by using an external magnetic field to guide the spins of the atoms forming the condensate."

In 2009, Aalto University researchers Ville Pietilä and Mikko Möttönen published theoretical results demonstrating a method to create Dirac monopoles in a Bose-Einstein condensate. The idea involves using external magnetic fields to rotate the atomic spins. A Dirac monopole forms in the condensate as a result of the spin rotation. This method was adopted by the researchers in creating the synthetic magnetic monopole.

The Dirac monopole forms in the artificial magnetic field of the condensate, not in the physical magnetic field which steers the spin degree of freedom. Thus, a natural magnetic monopole is not needed to create the synthetic monopole.

The Bose-Einstein condensate

"A Bose-Einstein condensate behaves like a single giant atom, even though it can contain millions."

A Bose-Einstein condensate is sometimes considered to be the fifth state of matter, in addition to solid, liquid, gas, and plasma. In the condensate, the importance and location of individual atoms becomes vague and the system behaves as if it were a single large atom. The first Bose-Einstein condensates were achieved in 1995, and this work received the Nobel Prize in 2001.

"Bose-Einstein condensates provide a window from our world into the quantum wonderland. The more often I peek at it, the more I want to stay there," says enchanted Dr. Möttönen. Since Bose-Einstein condensates contain many atoms, photographs of them can be taken using technology that is in part similar to that used in ordinary digital cameras. In addition, the condensates can be forced into the desired shape by means of external magnetic fields and laser beams. These properties make condensates a unique tool for developing new phenomena and quantum technologies. In addition to being used with magnetic monopoles, condensates can simulate the properties of various useful materials to the accuracy of a single atom. One of the daydreams of condensate researchers involves finding a solution for the development of superconducting materials that function at room temperature.

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Monopoles are impossible due to the fact that nature always maintains balance and such a thing as a monopole would not be balanced. If a monopole was somehow created, it would instantaneously revert back into whatever it was created from.

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Couldn't you use exactly the same reasoning to say that there cannot be charged particles? We know this isn't true because electrons and protons exist. – Peter Shor Jul 15 '13 at 21:54
Electrons have negative charge and protons have positive charge. Positive and negative charges are not the same as north and south poles. Electric charges and magnetic poles being synonymous is a very common misconception held by those who are not adequately familiar with electricity and magnetism. – Ben Jul 16 '13 at 1:20
Also, though one can induce the other, they are in fact two different forces. – Ben Jul 16 '13 at 1:27

## protected by Qmechanic♦Jul 15 '13 at 21:29

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