Magnetic Monopoles - Missing Piece of the Symmetry

Review

Divyansh Dewan

  This article encompasses a brief about magnetic monopoles & reflects upon how their existence has been predicted, but they haven't been directly observed.
  It also talks about why we believe they exist, how they are envisioned, how they fit into the larger framework of science, the challenges in finding them & the efforts taken by scientists to observe them.

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  There's always that one over-smart person in the class who knows more than others. The one who knows about quantum entanglement, vector calculus or can derive Maxwell's equations, but can they?

Paul Dirac   What proof do they have of Gauss's law for magnetism, best summarized as "Magnetic monopoles do not exist." Cause I don't recall ever seeing any proof for that. And indeed, there isn't any. Paul Dirac was the first to propose the idea of magnetic monopoles in 1931 and in fact, the standard model of particle physics also predicted the existence of magnetic monopoles.

  For those unacquainted with this term, a magnetic monopole is a particle having only one kind of net magnetic charge - either north or south, (which we have been told does not exist, in school) Well, they probably don’t, until we dig a little deeper.

  We must first understand why it is believed that magnetic monopoles do not exist. There is nothing as such that prevents the magnetic monopoles from existing. As mentioned above, current theories on particle physics predict their existence. But they have never been detected, nor have their effects been directly seen.

  Paul Dirac envisioned magnetic monopoles as a semi-infinitely long, infinitesimally thin solenoid (called the Dirac string). The end of such a solenoid acts like a magnetic charge, but it makes sense to identify this object as a magnetic monopole only if no conceivable experiment can detect the infinitesimally thin solenoid. He proved that such a solenoid would be undetected to an electron interference experiment if the magnetic charge (g) is quantized and these lead to magnetic monopoles.

  Magnetic monopoles are hypothesized to be massive particles - around 19 orders of magnitude heavier than a proton and require extremely high energies to be created. It is possible that in the early age of the universe, the temperature might have been hot enough to facilitate their formation, but again they haven't been detected (and not for lack of trying).

  Just as the sun and the earth have their own magnetic fields, entire galaxies also have their magnetic fields. Given time, the monopoles formed during the early universe should have been able to discharge these fields (just like electric charges can discharge the electric field between plates of a capacitor), but evidently, they haven't. Why? It's not that they can lose their magnetic charge over time by dissociating into uncharged smaller particles. Magnetic charge, just as electric charge isn't lost and remains conserved. Instead of discounting their existence, rather we concluded that the early universe must have been expanding at a much faster rate than we had earlier thought. This rapid expansion diluted the concentrations of the already hard-to-produce monopoles to the point where they won't be able to discharge the fields of entire galaxies.

  All of this is fine, but let’s take a step back and think about it. Since 1931 physicists have been searching for magnetic monopoles in cosmic rays; trapped in bulk matter, in lunar dust, meteors, and at accelerators where they would be produced in high-energy particle interactions with no success. We alter our understanding of the early universe to account for these monopoles that no one has observed. All this when one of the four fundamental statements of electrodynamics state that they don't exist. Why are we so determined to prove ourselves wrong?

  It is because Paul Dirac proved that Maxwell's equations can be modified to account for magnetic monopoles and still have quantized electric charge. All of our unified theories, from the standard model to quantum electrodynamics, predict their existence. But more than that, nature loves symmetry. Electricity and magnetism are already so tightly intertwined that the idea of electric monopoles existing but not magnetic monopoles just don’t feel right in the minds of physicists. While this is in no way to prove their existence, it is definitely an indication of it.

  So, where are we most likely to find these elusive particles? Earlier it was believed that the only viable way to detect monopoles would be by looking deeper into the cosmos to detect those formed in the early universe. But nowadays, the most promising source seems to be CERN.

  In 2010, the Large Hadron Collider (LHC) approved its seventh experiment - the Monopole and Exotics Detectors at the LHC (MOEDAL), specifically designed to detect monopoles that may form in the LHC. This detector is like a giant camera waiting to photograph the tell-tale signs of these new particles. These monopoles would rip through the detector, creating a minute trail of damage through it.

The MoEDAL experiment   The MOEDAL experiment has already helped us narrow the energy window where these monopoles would be formed and the scientists at CERN are optimistic about getting more precise data from it.

Bibliography

1. MoEDAL closes in on search for magnetic particle
2. Magnetic Monopoles
3. Inflation
4. ATLAS homes in on magnetic monopoles

Divyansh is a first-year student enrolled in the BS-MS program at IISER Kolkata. He is interested in physics and astronomy. Apart from that, his interests mainly lie in gaming and reading-particularly fiction.