Why Magnetic Monopoles SHOULD Exist
PBS Space Time・14 minutes read
Physicists have long sought magnetic monopoles as distinct from tachyons or supersymmetric particles, but classical electrodynamics explains their absence due to the linkage between magnetic fields and moving electric charges. Quantum mechanics initially seemed to prohibit magnetic monopoles, but Paul Dirac's 1931 prediction challenged this idea based on a concept known as the "Dirac string," with Hans Ohanian suggesting spin as a circular charge current in the Dirac field, although this explanation is not universally accepted.
Insights
- Classical electromagnetism explains why magnetic monopoles have not been observed, as splitting a magnet does not result in isolated magnetic charges due to the nature of magnetic fields and their divergence.
- The Pauli exclusion principle dictates that fermions, like electrons, cannot occupy the same quantum states, preventing collapse under degeneracy pressure. This principle is crucial in understanding phenomena like electron capture in collapsing stars and the unique behavior of particles such as USB plugs with a spin of 2/3.
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Recent questions
What are magnetic monopoles?
Hypothetical particles with isolated magnetic charges.
How did Paul Dirac contribute to magnetic monopole theory?
Predicted their existence mathematically in 1931.
What is the significance of Gauss's law for magnetism?
Asserts magnetic fields have zero divergence.
How does Murray Gell-Mann's principle relate to magnetic monopoles?
Suggests if theory permits, they exist in nature.
What is the Pauli exclusion principle's role in particle interactions?
Ensures fermions never occupy same quantum states.
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Summary
00:00
Quest for Magnetic Monopoles: A Historical Perspective
- Physicists have long sought magnetic monopoles, distinct from tachyons or supersymmetric particles, as a probable existence.
- A metal bar with electrons forced to one end creates a dipole electric field; cutting it in half results in separate positive and negative electric charges.
- Magnetizing a metal bar produces a dipole magnetic field, but splitting it does not yield isolated magnetic charges due to classical electromagnetism.
- French scholar Petrus Peregrinus de Marincourt's 1269 experiment revealed that halved magnets still generate dipole fields, not magnetic monopoles.
- Classical electrodynamics links magnetic fields to moving electric charges, explaining the absence of magnetic monopoles.
- Gauss's law for magnetism, a Maxwell equation, asserts that magnetic fields have zero divergence, precluding magnetic monopoles.
- In contrast, Gauss's law for electric fields allows for isolated electric charges, as the divergence of the electric field is not zero.
- Physicist Murray Gell-Mann's principle suggests that if physical theory permits it, then it exists in nature, hinting at the potential existence of magnetic monopoles.
- Quantum mechanics initially seemed to forbid magnetic monopoles due to the nature of magnetic fields and their divergence, unlike electric fields.
- Paul Dirac's mathematical prediction of magnetic monopoles in 1931, based on a concept called the "Dirac string," challenged the notion of their non-existence.
15:16
Electron Spin and Pauli Exclusion Principle
- Electrons in atoms can occupy the same energy level but different quantum states due to opposite spin orientations, allowing for two electrons in one energy level. Spin can be described as a circular charge current in the Dirac field, as suggested by Hans Ohanian in his book "What is Spin?", although this explanation is not universally accepted.
- The Pauli exclusion principle ensures that fermions never occupy the same quantum states, with degeneracy pressure supporting against collapse. When this pressure is overcome, such as in collapsing stars, electrons can be captured by protons, converting them to neutrons and reducing degeneracy pressure to allow for gravitational collapse. USB plugs, with a spin of 2/3, do not follow the standard model of fermions or bosons, requiring a 540° rotation to return to the correct orientation, a phenomenon not explained by spin statistics.
