This needs to be understood from the microscopic origin of solid magnetism. In fact, the electron in the material itself has a spin magnetic moment-just like an extremely tiny magnet, and the electron orbiting the nucleus like a planet orbiting the sun will produce the orbital magnetic moment, the superposition of the orbital magnetic moment and the spin magnetic moment The total magnetic moment of the electron is formed (the nucleus itself also has a small magnetic moment). Different electronic arrangements will lead to different magnetic sizes of the atoms themselves. Among them, transition metals such as iron, cobalt, nickel, manganese, neodymium, and rare earth metal elements are more magnetic.
When these magnetic atoms are aligned in the same direction in the solid material, the material appears magnetic. For example, the main component of our common natural magnet is Fe3O4, because the magnetic moments of iron are aligned to form strong ferromagnetism. If the atom itself is weak, it is difficult for the material to have strong magnetism. If the magnetic moments of the material are arranged in a disorderly manner, they will not be magnetic.
Knowing the source of magnetism, it is easy to understand why the N pole and S pole always appear in pairs. Because the overall magnetism of the magnet comes from the magnetism of the atoms inside the magnet, and the atom itself is like a tiny magnet with two magnetic poles, N and S, that is to say, the magnetic poles appear in pairs in the microscopic view, so no matter what the macro view is. Cutting the magnet will always get two pairs of magnetic poles.
Then, is there a kind of particle microscopically that only has a single magnetic pole among the N pole or the S pole? In electromagnetics, people have known the existence of electric charge for a long time, but physicists have never discovered particles with a single magnetic pole. The British physicist Dirac used mathematical formulas as early as 1931 to predict that particles with a single magnetic pole can exist, which is called "magnetic monopole" in physics. He believed that since electrons with basic charges exist in the universe, particles with basic "magnetic charges" should exist.
The most basic law of electromagnetic theory is a system of equations composed of four equations-Maxwell's equations. Its position in electromagnetics is the same as that of Newton's law of motion in mechanics. All electromagnetic theories are based on this Based on the system of equations. However, the existing Maxwell equations do not consider magnetic monopoles.
If the existence of a magnetic monopole is confirmed, only a slight modification to the existing Maxwell equations is enough, and what is surprising is that the modified equations become more symmetrical, that is, the existence of a magnetic monopole It will make "electricity" and "magnetism" more symmetrical. This has stimulated the research interest of many physicists and embarked on the arduous journey of searching for magnetic monopoles. In history, many scientists claimed to have accidentally found traces of the existence of magnetic monopoles in experiments. Unfortunately, these results have never been repeated. However, all this has not stopped scientists from searching for magnetic monopoles.