The Three Big Secrets of Magnetic Phenomena
Magnets and magnetism are ubiquitous in our daily lives, helping us find our way in unfamiliar wilderness and keeping the refrigerator door shut at home. In addition to these common examples, magnetic phenomena can sometimes play a role in certain situations, such as in MRI scanners, where magnetic fields can play an important role.
As common as it is, magnetism holds some pretty cool secrets.
Only motion produces magnetism
A charged particle, sitting there alone, doing nothing, generates an electric field. This field spreads from the particle in all directions and instructs other nearby charged particles how to respond. If there is an identically charged particle nearby, it will be pushed away; if there is an oppositely charged particle far away, it will be pulled slightly closer.
But if you put charged particles in motion, something amazing happens: a new field emerges! This strange field has a strange manifestation: the direction of the field is not pointing directly at the particle or away from the particle, but rotating around the particle, perpendicular to the direction of particle motion. In addition, nearby charged particles can only feel this new field if they are in motion, and the direction of the force felt by the particles is also perpendicular to the direction of its motion.
The Three Big Secrets of Magnetic Phenomena
We call this field the magnetic field, which is caused by the moving charges and only affects the moving charges. But the magnets in your refrigerator aren’t moving, so why are they still magnetic?
Your magnet itself is not moving, but the matter that makes it up inside is moving. Each atom in a magnet has layers of electrons, which are charged particles that have the property of spin. For ease of understanding, we can think of spin electrons as small spinning balls, although this analogy is strictly speaking incorrect, because spin is actually a very esoteric quantum property.
In this way, the spin of the electron is equivalent to the rotation of the electron, and the rotation is also a kind of motion. Thus, each electron can generate a weak magnetic field. In most materials, the orientation of each electron spin is randomly distributed, and the resulting magnetic fields cancel each other out on a macroscopic scale. But in a magnet, many electrons spin in roughly the same direction, and the resulting combined magnetic field is strong enough to manifest itself on a macroscopic scale.
Magnetic monopoles are possible
All the magnetic fields we see in the universe are generated by moving electric charges, so magnetic south and magnetic north always come in pairs, and there is no way to separate them. If you take a magnet and cut it in half, what you end up with are two smaller, weaker magnets — their inner electrons are still spinning, just as before.
This property of magnets is well known. In the 19th century, the British physicist James Clerk Maxwell successfully unified the electrical and magnetic phenomena under a theoretical framework, and he also directly wrote the idea that “there is no such thing as a single magnetic pole” into his equations – the famous Maxwell’s equations. For decades, scientists have never questioned this idea.
But our growing understanding of quantum mechanics, as we begin to study the wondrous microscopic world, throws some doubts on the above ideas. A pioneer in the quantum field, British physicist Paul Dirac first noticed this problem in the 1930s.
Using quantum mechanics calculations, Dirac found that if there is a hypothetical elementary particle with only a single magnetic pole, north or south, in the universe, that is, a magnetic monopole, then all charges in the universe must be quantized. That is to say, if a magnetic monopole exists, then the electric charge must be an integer multiple of a certain constant. In reality, physicists have long discovered through experiments that charge is indeed quantized, and this specific constant is the basic charge, which is the charge carried by a proton or the amount of negative charge carried by an electron. Dirac’s research showed that there might be magnetic monopoles in the universe, but until now, physicists have not found any magnetic monopoles.
Magnetic monopoles are a frontier topic in physics today, and many physicists are still sparing no effort to find this mysterious particle. Because many cutting-edge physical theories include magnetic monopoles, if such a particle exists, it must have a huge impact on physics.
Magnetic phenomenon is the key to the establishment of special relativity
The connection between electricity and magnetism that Maxwell discovered was more than a superficial one. He realized that electricity and magnetism were like two sides of the same coin: a changing electric field could create a magnetic field, and vice versa. Moreover, light is actually a phenomenon produced when oscillating electricity and magnetism interact.
Einstein was a huge fan of Maxwell’s theories, and he thought about things Maxwell never thought of. Einstein realized that there was a connection between electricity, magnetism, and motion. Also, imagine a charged particle, sitting there alone, what would happen if you started running over it?
From your perspective, the charge appears to be moving. What does the moving charge do? Yes, they generate magnetic fields. So, not only are electric and magnetic fields two sides of the same coin, but you can convert one side of the coin to the other with a simple movement. This also means that electric and magnetic phenomena are relative, and that different observers will disagree on what they see: some stationary observers may see an electric field, while some moving observers will see the electric field Where there is also a magnetic field.
According to the above train of thought, Einstein continued to analyze, and finally created the special theory of relativity in 1905, and established a new view of space and time. Under this view of time and space, except for electric and magnetic phenomena, mass, length and time are all relative, and the observation result depends on the motion state of the object relative to the observer. For example, for an observer, the faster the spaceship moves, the slower the observer detects the passage of time inside the ship, which is known as the time dilation effect. The special theory of relativity is the cornerstone of modern physics, and its creation process is inseparable from the magnetic phenomenon.
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