A magnetic monopole is an isolated pole of a magnet that serves as an elementary particle in the field of Particle Physics. It can be either a single North or a single South Pole with a net magnetic charge on it. Its existence is purely hypothetical as according to the magnetic theory, even the smallest part of a magnet comes with two poles, north and south. Still a monopole is essential for defining certain physical quantities and doing calculations in the fields of electromagnetism and magnetism.
According to the String theory, monopoles always have a finite mass. The magnetic field lines spread out radially in all directions, with no looping back inside as seen in magnetic dipoles. On passing through a superconducting loop, it induces a distinct signal that is equally sensitive at all velocities and masses.
English Theoretical Physicist Paul Dirac, in his paper published in 1931, propounded the idea of the quantum theory of magnetic charge. He showed that magnetic monopoles could explain the quantization of electric charges in the universe. As the presence of quantized charges is a known fact, since then searches have been on to identify monopoles. Though a considerable number of scientists and researchers claimed to have found it, many of these discoveries were either found to be inconclusive, inconsistent or not at par with experimental evidence.
A handful of them believed that they could be produced in large numbers in photon exchange of particle accelerators and should be detected as the photons get scattered. The results of such tests were also not favorable. However, some were successful in reproducing these particles in lab environments.
Artificial Monopole Discovery
In May 2013, scientists from Cologne, Munich and Dresden managed to create synthetic magnetic monopoles by merging small magnetic whirls or skyrmions. According to a paper published on 29th Jan 2014, a collaboration between Prof. David S. Hall of Amherst College and Aalto University Academy research fellow Mikko Möttönen was able to create, detect and photograph artificial magnetic monopoles in the lab. For this, they cooled rubidium atoms to temperatures near absolute zero to create monopoles in the quantum-mechanical field describing the gas.
London Centre for Nanotechnology (LCN) scientists also provided evidence of the existence of unipolar magnets in nature by using special neutron scattering techniques. This could give people an insight into the properties of magnetic monopoles as predicted by Dirac. Hyperbolic monopoles at the centre of hyperbolic spaces have been a subject of extensive research. Some have also conducted a search by neutrino telescopes utilizing massive light emission. That topological insulators can induce magnetic monopoles has been proposed by certain physicists as well.
Condensed-matter physicists could reproduce the monopolar magnets artificially in oxide crystals of rare earths called spin ices where the electrons behave like a cluster of monopoles near absolute zero temperatures. The unipolar particles so formed are not considered to be real particles like protons and electrons. Instead, they are referred to as quasi-particles since their appearance is a result of a collective behavior of the surrounding electrons and atoms and they can interact with each other. Replicating these elusive particles in synthetic environments without violating any laws of Physics has paved the way of finding the real particles.
Magnetic Monopole for the Grand Unified Theory
The grand unified theory (GUT) aims to merge the four fundamental forces in nature, that is, electric, magnetic, gravitational as well as strong and weak nuclear forces, into a single force. A significant step was taken in this regard with the formulation of the laws of electromagnetism by Scottish scientist James Clerk Maxwell in the 19th century, by which he linked magnetism with electricity.
The theory of quantum mechanics could unify all the other forces except gravity. While most of the particles appearing in the quantum field theory are unstable and decay into other particles obeying the laws of conservation, the monopolar magnets predicted by GUT remain stable, but not because they satisfy any conservation condition. It is because there are no simpler topological states into which they can decay. The Kaluza-Klein theory tries to merge gravity with electromagnetism by assuming the existence of a fifth dimension beyond space-time.
Dirac String and Magnetic Monopole
Conceived by Paul Dirac, two Dirac magnetic monopoles of opposite magnetic charges or a single magnetic monopole and infinity are connected by a hypothetical one-dimensional curve in space called Dirac String where the gauge potential cannot be defined. It provides a way to include magnetic monopoles in Maxwell’s Equations on electromagnetism. It may be mentioned here that the gauge potential relates to the gauge theory in which the Lagrangian does not change through a continuous group of local transformations.
Black Holes and Magnetic Monopole
If an electric charge is kept at rest outside a magnetically charged black hole, then the situation can be thought to be equivalent to monopole placed near an electrically charged black hole by electromagnetic duality. In that case, the total angular momentum of the system is given by the standard value for a pair of charged monopoles. But, once the charge is captured by the black hole, the associated angular momentum loses all of its exotic origins and it seems to resemble ordinary rotation from outside.
Magnetic Monopole Prediction by the Big Bang Theory
The Big Bang Theory takes the help of GUT to explain the creation of nuclei in the present universe. If the GUT can be proved to be correct, then massive monopoles should exist. However, inability to find any such single pole particles in nature contradicts the former theory itself.
Magnetic Monopole in Cosmology
Some scientists predicted that if dark matter could exist, then there was a high probability of them being formed of massive magnetic monopoles. Some also propose that these particles could be the tools of cosmological inflation, that is, the expansion of the universe due to the flow of new space through portals in space-time.
Magnetic Monopole Concept in Other Physical Laws
Gauss’s Law was modified for magnetic fields as the magnetic flux through any closed surface is zero, in the absence of magnetic monopoles. Hence, an analogy with the law in electrostatics could not be applied here. Lorentz forces, however, can be modified in conformity with the particles.
A modification in the monopole theory implies a possible C-violation of electromagnetic interactions. Physical laws maintain symmetry under a charge-conjugation transformation. This is known as C-symmetry, which may be violated by some weak interactions.
Discovering a natural magnetic monopole could revolutionize the field of science as this will be at par with great discoveries like those of the proton or electron. Their existence can also give us valuable knowledge on the fundamental nature of the universe and how the basic forces of nature are related to each other. Though it is still hard to predict, it could help to make devices that perform accurate computations and store energy or information in new ways.
They can make matter strong enough to resist nuclear explosion and can produce magnetic levitation. Monopole magnet motors can make free energy generators that convert normal matter into pure energy. Universitat Autònoma de Barcelona scientists in 2015 could create the first experimental wormhole in the lab using the concept of single pole magnets.
Though it is still a distant dream, rockets propelled by magnetic monopoles might provide future spaceships with enormous levels of speed and energy for interstellar travel. In gauge theories, true magnetic monopoles can provide regular solutions to the field equations involving the electromagnetic group. One of its theoretical uses would be to induce controlled fusion in plasma. Some people claim to have made motors for perpetual motion using these particles, but their validity remains to be examined.
The assumption that there may be a potential danger from them since they can act as catalysts for proton decays is baseless. According to CERN labs during their experiments with the Large Hadron Collider (LHC) on vacuum bubbles, strangelets, and monopoles, the cosmic radiation reaching the earth could already be producing them. Still, the shielding effect of the earth and other heavenly bodies protects us from any hazard.
Though a significant breakthrough has been achieved in their discovery, understanding the structure of magnetic monopoles and other topological entities are also important since they appear in the models that describe the early Universe and influence the properties of many materials, e.g. metals.