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You've seen this a thousand times. Magnets pulling things. Even with very large weights, it almost seems magical that this invisible force can be so powerful. Why do magnets attract? What is the mechanism? What's actually happening behind the scenes at the atomic and quantum level? We're going to keep asking why questions until we get to the ultimate answer. And that answer is way more fascinating than you might think. And it's probably something you've never seen before. That's coming up right now.
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You've probably learned in school that magnets have a north pole and a south pole, and opposite poles attract while like poles repel. But that's really just basic. It doesn't tell us anything. To truly understand magnetism, we need to zoom all the way in down to the atomic level. Magnets are made of atoms, and atoms are composed of positively charged nucleus surrounded by negatively charged electrons. These electrons are tiny charged particles that orbit the nucleus. Kind of like planets orbiting a star. Well, not exactly, but we'll get into that later. For now, let's just visualize electrons orbiting the nucleus like planets around the sun. For simplicity, the animation you see here is a decent mathematical approximation.
Each electron doesn't just orbit randomly. Electrons have a quantum property called spin. Spin is not easy to visualize because it is a quantum property. It's not exactly like a spinning top, but it is a type of intrinsic angular momentum that particles possess. Even though they don't physically rotate, it's intrinsic, meaning it's a property that electrons have similar to the way they have a negative charge. Each spinning electron generates its own miniature magnetic field. The magnetic field lines represent the strength and direction of the force another magnetic material would feel in the vicinity of the magnet.
Now, most materials have electrons spinning randomly in all sorts of directions. So their magnetic fields cancel each other out resulting in no overall magnetism. But in certain materials like iron, cobalt or nickel, something special happens. In these special materials, electrons tend to align their spins with each other due to quantum mechanical interactions. I'll explain what those interactions are in a minute. When electrons align their spins in this synchronized way, their tiny magnetic fields combine, becoming stronger and stronger. Large groups of aligned electrons create microscopic regions called magnetic domains where all electron spins point in the same direction creating a strong local magnetic field.
Initially these domains themselves are randomly oriented canceling each other out at large scales. So the material overall is not magnetic. But when you magnetize a piece of iron by exposing it to another magnet or electric current, you force most of these domains to align in the same direction, turning the material now into a magnet. So that's how we create a magnet.
Okay, but we still haven't answered the big question. Why exactly do magnets attract each other? The standard classical explanation, which you've probably heard before, is this. Magnets interact through their magnetic fields. These fields are like invisible patterns or lines coming out of the north pole and going into the south pole. You can even see these patterns if you sprinkle iron filings around a magnet. The filings line up neatly along these invisible field lines.
When opposite poles of two magnets get close together, their field lines naturally flow from one magnet to another, creating a continuous loop, a stable, lower energy state. Nature loves lower energy. So this configuration pulls the magnets together. Conversely, when two like poles face each other, their field lines clash. They don't flow smoothly into each other, but push against one another, creating tension or pressure that drives them apart. This is the standard explanation you'll get in high school and some college courses.
But since you're watching my channel, I know that like me, you would find that explanation highly lacking. What's really going on at the quantum level? So, let's go real deep right now. First, what exactly are these field lines? At the deepest level, magnetism is explained through quantum electronamics or QED. QED is the theory that describes the electromagnetic force, which is one of the four fundamental forces of nature. It is perhaps the most well understood theory in quantum mechanics. I have a couple of videos on this. I'll leave a link in the description if you want to know the history of QED and how some brilliant scientists figured this out.
According to QED, magnetic forces result from the exchange of tiny particles called virtual photons. These virtual photons act as messengers, constantly exchanged between charged particles and magnetic poles, communicating the electromagnetic force. Imagine two people in boats tossing a ball back and forth. Each time the ball is thrown and caught, they push each other apart slightly. Now imagine these two same individuals throwing boomerangs to each other. Each time they do that, they move closer together. Virtual photons are like invisible balls and boomerangs exchanged between magnets, resulting in attraction or repulsion.
This virtual photon exchange is something that all charged particles do. That's what a charged particle is. Why do they do this? What is a charge? We don't know. We just know that it's a property that some particles possess, and we know how that property works. But wait, what the heck are virtual photons? It's going to sound weird if you haven't heard of virtual particles before. You're probably familiar with regular photons, which are packets of energy that make up light waves, but they can also exist as small quantum fluctuations of energy in the vacuum. These are exchanged between particles interacting by the electromagnetic force. In this case, they're called virtual because they exist so briefly, popping in and out of existence that they can't be measured.
Why do they pop into and out of existence? It's a consequence of quantum field theory or QFT, which is the best and most proven theory of reality that we have. I have a couple of videos on this if you want to know the details. But to summarize, in QFT, all fundamental particles are excitations in quantum fields that are everywhere in spacetime. But these fields are not static. Even in the vacuum of empty space with no matter or radiation, it's teeming with virtual particle antiparticle pairs being created and destroyed constantly. But virtual particles are not just theoretical curiosities. They mediate interactions between real particles. For example, when an electron emits a virtual photon, it can interact with another charged particle, effectively causing a force. The virtual photons are not measurable directly, but we can measure their effects.
Now, if you're satisfied with what you've heard so far, you don't need to watch the rest of this video because now I'm going to go rabbit hole quantum on you. I'll explain things as deeply as I think we can go. So, here is the in-depth explanation from a purely quantum mechanical perspective.
At its most basic quantum level, magnetism comes down to electrons. Electrons exist in clouds of probability around the nucleus of atoms. The clouds represent the probability of finding the electron somewhere there if we were to measure its location. These clouds of probability are what we call an atom's orbitals, which describe possible locations for the electrons. And what we call shells are groups of orbitals containing electrons at the same energy level. These electrons have two important intrinsic quantum properties that are important for this explanation. They have a negative electrical charge and they have a quantum spin. But mathematically electrons are approximately tiny particles orbiting the nucleus of atoms and they are approximately spinning like you see in this animation. The spin can be up or down. Because electrons have an electric charge, their spin creates a tiny magnetic field. So each electron acts like a miniature magnet. Its spin orientation determines its magnetic poles.
The crucial quantum mechanical detail here is that the electrons obey something called the Pauli exclusion principle. This principle simplified says that two identical electrons can't be at the same place at the same time. And this is the key to understanding why materials become magnetic in the first place. But first you might ask what's the basis of the Pauli exclusion principle? Why can't two identical electrons be at the same place at the same time? This has to do with their wave functions. All fundamental particles are essentially waves defined by wave functions which can be calculated using the Schrödinger equation. Approximately the square of the wave function of an electron represents the probability of finding the electron in a certain location. The wave functions of two identical electrons interfere or combine in such a way that their wave function becomes zero. You can think of this as the probability of finding them together becomes zero. So this is just not going to happen.
Since for a given orbital electrons are identical to each other except for their spin orientations, you will only find oppositely spinning electrons together in any orbital of an atom. In materials where all electrons pair up, one electron spinning up paired with another electron spinning down, the magnetic fields cancel each other out, resulting in no overall magnetism. But lots of atoms have unpaired electrons in their shells. But not all of these are ferromagnetic. So let's look at why.
Quantum mechanically unpaired electrons in any atom shell generally align their spins that is spin in the same direction. Why? Because the wave function overlap of unpaired electrons in a given shell is such that it is more energetically favorable for them to have parallel spins rather than opposite spins. The wave function of parallel spinning electrons interact in such a way that they move further apart which lowers their repulsive interaction. Electrons only pair up with opposite spins in a particular shell of an atom when the number of orbitals in the shell runs out to accommodate lone electrons. This is called Hund's rule where electrons first singly occupy available orbitals before pairing up in any of the orbitals. This rule applies to all atoms and not just ferromagnetic materials.
But ferromagnetic materials like iron, cobalt and nickel have another special property that results from their atomic lattice structure due to a quantum mechanical effect called exchange interactions. What is this? It's a subtle but very important quantum mechanical force that arises from the overlap of electron wave functions between neighboring atoms. When electrons from neighboring atoms in the material have parallel spins, their spatial wave functions interact in such a way that allows electrons to stay slightly further apart on average, which reduces their electrostatic repulsion and lowers the energy of the lattice. If electrons have antiparallel spins and adjacent atoms, their wave functions overlap more closely increasing the repulsive interaction making the arrangement slightly higher in energy and lower energy is always preferred.
This overall alignment of spins does not happen in non-ferromagnetic materials even if they have a high number of unpaired electrons. Take for example manganese. It has more unpaired electrons than iron but it's not ferromagnetic. Why? Because the electrons of adjacent manganese atoms in their lattice structure interact differently. Their unique structure and symmetry favors aligning spins of electrons and adjacent atoms antiparallel or in complicated patterns instead of all parallel. Only in ferromagnetic materials is the interaction of the adjacent atoms such that parallel spins are favored for the material overall which results in an overall magnetic effect on the metal. So now we know why some metals can become magnetic while others cannot.
Now the remaining question is why do magnets sometimes attract and sometimes repel depending on how you hold them? It boils down to the spin alignment and quantum symmetry of electron wave functions in the magnets. When two similar poles approach north to north, south to south, their electron spins are aligned in opposite ways relative to each other. One magnet has electron spins oriented up and the other magnet oriented down relative to it. In quantum mechanical terms, this arrangement creates interference patterns in their electron wave functions making it energetically unfavorable for electrons to occupy overlapping states. This raises the energy making the system want to avoid that state causing them to push away. The electron wave functions from one magnet interferes negatively with those of the other magnet. A higher energy state is created in the space between the two similar poles. The materials want to avoid that space and move to a lower energy space which is away from each other. It's like pushing the two magnets up a hill which has higher potential energy as shown in this animation. The lower potential energy is away from each other.
When opposite poles approach each other, electron spins from one magnet align nicely with spins in the other magnet. Their electron wave functions overlap constructively, lowering their combined quantum energy. A lower energy, more stable state is formed in the space between the poles. So the magnets spontaneously move to that space. That is, they move closer together. It's like the two magnets going down a hill to the bottom which has lower potential energy closer to each other as shown in this animation. So quantum mechanically attraction and repulsion arises from subtle shifts and electron wave function interference patterns controlled by spin alignments and exchanges of virtual photons.
We've covered a lot of material here but this is the overall summary picture I want to leave you with. Electron spin creates tiny quantum magnets. Exchange interactions align electron spins in the lattice structure of materials like iron. Align spins produce large scale magnetic fields. Magnets interact through exchanges of virtual photons which are excitations in the quantum electromagnetic field. Attraction and repulsion results from how electron spins and wave functions overlap and interfere quantum mechanically.
I hope this gives you a deeper understanding of magnetism than what you may have been taught in school. I can't emphasize enough how important it is if you want to really learn this or any subject more deeply to master the foundations of critical scientific thinking. Curious questioning and skepticism is the hallmark of a scientifically brilliant mind and that's the foundational skill you learn at brilliant.org, our sponsor today. I love the Brilliant app because it builds critical thinking skills through hands-on problem solving, not memorizing. This method works best for me and it's also proven to be six times more effective than watching lectures. You'll develop a scientific intuition through visual, interactive, hands-on problem solving. You'll learn to think like an engineer, which as you probably know, I am. But Brilliant will not only help you become a better thinker, but also a problem solver. With thousands of visual interactive lessons in math, science, programming, data analysis, and AI, fun learning will be at your fingertips, whether at home or on the go.
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