Magnetic Monopoles Emulated


Yesterday there was a news item about the creation of a magnetic monopole. Although the news accounts are far above average for the usual explanations of a scientific breakthrough, most still leave a lot to be desired. For instance not all of them distinguish between the elementary particle and the quasiparticle that was what was created here. The best new account that I could find was written by a reporter for nature magazine at Quantum cloud simulates magnetic monopole, which sums up the work remarkably well. If you would like a slightly more in-depth account, keep reading.

Physics students who have taken electromagnetic theory will probably remember that Maxwell’s equations weren’t quite symmetric. Because of that, magnetism can only show itself as a dipole, quadrapole, etc. By symmetrizing the equations, they predict a magnetic monopole similar to electrically charged particles which are also monopoles. If you are familiar with the Maxwell equations, this means changing the Gauss magnetic law, the Faraday induction law, and the Lorentz law.

This is all discussed in an excellent article in Wikipedia: Magnetic Monopoles.

P.A.M. Dirac showed that an electrical charge has to exist as a quantized particle and in 1931, he made the initial attempt to extend this to a magnetically quantized monopole. A similar result comes from magnetic fields when they are considered as Yang-Mills fields. This was first derived as the ‘t Hooft–Polyakov magnetic monopole in 1974. All singularities were removed and there appeared to be little reason to doubt their existence – other than the fact that they had never been found.

Maxwell’s equations and Lorentz force equation with magnetic monopoles: SI units

Name

Without magnetic monopoles

Weber convention

Ampere·meter convention

Gauss’s Law

Gauss’s Law for magnetism

Faraday’s Law of induction

Ampère’s Law (with Maxwell’s extension)

Lorentz force equation

If you have studied cosmological inflation, you know that Alan Guth was convinced that the big bang should have produced a preponderance of magnetic monopoles. There should have been no more reason for them to decay than for an electron to decay, so he was at a loss to explain why he was unable to detect any. Recalling Willem de Sitter’s solution to Einstein’s gravitational equation which included the cosmological constant, Guth realized that space must expand at an exponential rate, eventually exceeding the speed of light. This would dilute any initial matter to a point where measuring it is impossible, including magnetic monopoles. The expansion also creates negative energy which can only be balanced to zero by creating huge amounts of ordinary and dark matter along with residual vacuum energy created by a precipitous drop in the cosmological constant. Although this is only incidental to story of monopoles, it led to an important series of predictions about the universe and the big bang: Cosmological Inflation.

Although Guth showed that finding naturally occurring magnetic monopole elementary particles is futile, this has not stopped physicists from trying to create multiparticle conglomerates that behave as the elementary particle would.

Returning to the original Maxwell equations,

Name

Integral equations

Differential equations

Gauss’s law

Gauss’s law for magnetism

Maxwell–Faraday equation (Faraday’s law of induction)

Ampère’s circuital law (with Maxwell’s correction)

they contain the terms H [magnetizing field] and D [electrical displacement] rather than using B and E combined with permeability and permittivity as . In some experiments it is important not to combine them because without an elementary particle magnetic monopole, , which requires magnetic dipoles as the simplest solution. The genius to the conglomerate approach is that using H, it is possible to get around this restriction, even if the elementary magnetic monopole particle doesn’t exist. The beauty of this realization is that condensed matter can act as quasiparticles which can to manipulated by a macroscopic H field to behave in unusual ways.

In September 2009, this was applied to a dysprosium titanate spin-ice single crystal cooled to less than 2.0 Kelvin. The magnetic moments were shown to align into tubelike bundles that behaved like Dirac strings. Using an applied magnetic field to break the system symmetry, they were able to control the alignment and density of the strings. The defects at the end of each tube resembled magnetic monopoles.

Another article on February 11, 2011 described a related experiment on a dysprosium titanate single crystal cooled to .36 K. This time, using a magnetic pulse, the authors were able to create a field that lasted for several minutes. With a different method of measuring the parameters of the monopoles’ motions in the spin-ice crystal, they were able to identify both the free and bound magnetic charges.

Most recently on January 30, 2014, for the first time in a Bose-Einstein condensate of rubidium gas cooled to about 100 nano K the authors created a monopole quasiparticle. Each atom in the condensate has a magnetic field generated by electron spin which responds to an external applied magnetic field. The field of the condensate is controlled by the arrangement of the individual spins, represented by a property called vorticity.

By creating a vortex in the condensate, the magnetic field within the condensate changes direction around the vortex. When the vortex starts, the field is a simple dipole, and as it reaches half-way into the condensate, all magnetic field vectors either point in or out, creating a monopole quasiparticle. As the vortex continues to the other side all the way through the condensate, it creates a dipole pointing in the opposite direction from where it started.

There is a video showing this process, but without understanding the process, there isn’t much explanation for what is going on.

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4 responses to “Magnetic Monopoles Emulated

  1. I enjoyed reading that, although i profess i didn’t understand most of it. Does this support inflationary theory, or contradict it?

    (side question, have the results come in yet on gravitational waves?)

    • It’s neutral. The only way magnetic monopoles would contradict inflationary theory is for a naturally occurring elementary particle magnetic monopole to be found. Everything to date has been a quasiparticle conglomerate that acts the way the elementary particle is expected to behave.

      In spite of the extraordinary sensitivity of current gravitational wave detectors, I’m unaware of any signals being detected. As you probably know, gravitational waves come in different frequencies and types (transverse and longitudinal), and current detectors are only sensitive to particular ranges. Even with that stipulation, the events that would produce waves should fall in those ranges. At the time of the most recent event that should have been detectable (the merger of the contact binary V1309 Scorpii in March 2008) was not found by the LIGO detector as would have been expected. There are other events that it was hoped could be seen such as when a neutron star burps (a violent starquake, particularly in magnetars) that have also gone unobserved gravitationally. In 2010, physicists began dismantling LIGO to build an even more sensitive detector scheduled to be completed this year.

      Often when you see something about “gravity waves” in the news it’s about an entirely different phenomenon of the atmosphere, and the reporter doesn’t distinguish what is being reported or even worse, confuses this with Einstein’s prediction.

      Thanks for dropping by again.

      • I think I fall in that erroneous group. As far as I remember a satellite was up and gathering data which would either prove or disprove gravitational waves, therefore proving or disproving certain cosmological questions regarding inflation.

        How do you know all this? I’m impressed!

  2. I’ve just been lucky so far, and you’ve asked about something I’ve studied. There are real holes in what I know — like developmental biology, coordination chemistry, certain programming languages, almost anything in modern electronics, literature, languages, and the many places where I just don’t know how ignorant I am. The world is moving too fast for me to keep up.

    With your knowledge of the Bible, I’m surprised that you haven’t opened a megachurch. The world loves an obvious fraud — look at Benny Hinn, Kathleen Kuhlman, Father Devine, Amy Semple McPherson, and Ted Haggard. It doesn’t seem to make any difference how hard you push the boundaries of what is acceptable as long as you can blame is on someone else; Billy James Hargis could always blame the Communists for publicizing his homosexual activities. Years ago, I considered going into cryogenic burials (long before anyone else realized how much people hold onto the the hope for life) or preaching. Both of them turned my stomach, and I missed out on lucrative occupations.

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