So You Think Gravity Controls the Universe? Think Again

At the smallest scales, everything that happens is governed by forces. In quantum physics, these forces determine how matter behaves, how atoms form, and why the universe looks the way it does. In this video, we'll explore the three forces that dominate the quantum world, electromagnetism, the weak force, and the strong force, and see how they work together to shape our reality. That's coming up right now. What is electricity? All materials are made of atoms. Atoms have a positively charged nucleus and negatively charged electrons surrounding the nucleus. These electrons are bound to the nucleus due to their electromagnetic attraction to the oppositeely charged nucleus. But electrons in the outermost shell of the atom called the valance shell can sometimes become free when the material allows it. These freed electrons are called unsurprisingly free electrons and they can move through the material. This movement of electrical charge is what we call electricity. What we've just seen is that electric charge doesn't act in isolation. When charges move, they generate magnetic effects, revealing that electricity and magnetism are part of a single interaction. When alternating current passes through a coil, it produces a constantly changing magnetic flux per Maxwell's equations that say that changing electric fields create magnetic fields because again according to Maxwell's equations, a changing magnetic field creates a circulating electric field. This interaction governs light, electricity, magnetism, and chemistry. To understand how this actually works at the deepest level, we need to look at the quantum theory behind it. 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. So far, we've looked at forces that move electric charge and govern interactions. The weak force plays a very different role. Unlike the strong force, which binds particles together in the nucleus, we'll talk about that in a minute. The weak force allows particles to change identity and decay. Some types of atoms, radioactive processes can occur that modify the composition of a nucleus. The most well-known is alpha decay where a nucleus splits into smaller pieces by ejecting an alpha particle made up of two protons and two neutrons which is the same as a helium nucleus. This is mediated by the strong and electromagnetic interactions. However, the less common beta decay where a neutron transforms into a proton while emitting an electron and an anti-utrino cannot be explained by these two forces. Alpha particles could be explained using known forces, but beta decay could not. Something inside the atom was changing in a way that electromagnetism and the strong force simply could not account for. At first sight, the emission of an electron might look like an electromagnetic process. But the involvement of the neutron and neutrino which are not electrically charged means that this decay is instead the result of a whole new fundamental force. That force is called the weak force. The name is very fitting because it's a million times weaker than the strong force at fmptometer scales. The weak force operates at incredibly short ranges only about. 1% of the diameter of a proton. This is due to its mediators, the W and Z bzons. Unlike photons and gluons, these particles are massive, about 80 times the mass of a proton. This makes the

weak force short-lived and localized. Yet, it's the only force that's able to change the flavor of quarks, meaning it can change, for example, a down quark into an up quark, transforming neutrons into protons, and vice versa. This ability to transform particles is what makes radioactive decay possible. It determines how unstable atoms change over time, how nuclear reactions can proceed, and which elements can exist in stable forms. Without the weak force, the structure of matter and the evolution of the elements would be fundamentally different. But even the weak force cannot explain why atomic nuclei hold together so tightly. To understand that we need to look at the strongest force in nature. So now you have to ask since electromagnetism is so strong then multiple protons in the nucleus of any atom like helium and beyond should repel each other very strongly. According to Kulum's law, the two protons in a helium atom experience a repulsive force equal to about 90 newtons or 20 lb. For something as small as a helium atom, this is a huge force. They should repel each other and fly apart instantly. The reason that these protons don't fly apart is because they are kept glued together by a force that is even stronger than electromagnetism. About 100 times stronger called the strong nuclear force. To understand why this force works so differently from electromagnetism, we have to go deeper inside protons and neutrons to the level of quarks and the charges they carry. They're made of more fundamental matter particles called quarks and force particles called gluons. A proton and neutron each contain three quarks. A proton is made of two up quarks and one down quark, while a neutron is made of two down quarks and one up quark. Gluons within these nucleons are virtual particles, so the number fluctuates. We can't say exactly how many are inside, but there are eight total different types of gluons, which keeps quirks together. Both of these quirks and gluons carry what is called a color charge. It's analogous to an electric charge, but works via a completely different mechanism. And although it's called a color charge, it has nothing to do with optical colors that you can see with your eyes. It's just a metaphor to describe a different kind of charge that these fundamental particles associated with the strong force have. It is just a property that some particles have. And quantum chromodnamics provides a very good description of how the color charge works. An important thing to remember is that the color charge carried by gluons is not the same as electrical charge. And here's how the color charge works. There are three kinds of color charges, red, green, and blue. And the way to think of this is that red, green, and blue combine to make a neutral white. Analogous to the way it works for optical colors. So like electrical charges are conserved or balanced, positive with negative to make neutral. Color charges also have to be balanced by either a combination to make a neutral white or by color anticolor charges. That's right. There are anti-colors too like red and anti- red, green and anti- green and blue and anti-blue which also combine to become neutral. So any combination of color charges has to be either red, green and blue together or a color and anticol together such that we get a neutral color charge. The particle that mediates the strong force is the gluon. Now gluons bind quirks together by constantly exchanging color charge between them. Gluons mediate the strong force analogous to the way photons mediate electromagnetic force between particles with electrical charges. Very simply stated, it is this constant exchange of gluons carrying the color charge that causes the quarks to stay bound to each other. The constant exchange of gluons creates a kind of continuous bridge between quartz called a flux tube. Now, there's an important distinction between the way the strong force works with color charges versus the way electromagnetism works with electrical charges. Electromagnetism, like gravity, gets weaker as objects get further apart. The force between two quarks, however, actually gets stronger as they get further apart. It works like a rubber band or a spring. If you try to pull two quarks apart, the force between them gets stronger and stronger the further apart they are. This tends to pull a quark back into the protons or neutrons as they get further apart. However, if the quarks get too far apart, then the rubber band breaks. An interesting thing that happens at this point, the quark is not released, but the energy required to break the rubber

band creates a new quark and an anti-quark pair. This quark anti-quark pair is called a maison. It turns out that these maison act as the force carrying particle for the residual strong force that keeps them bound. It is a kind of residual force of the strong force and it's called the strong nuclear force. But note that this is distinct from the strong force which works within the nucleons keeping the quirks tightly bound together and that is mediated by gluons. But the strong nuclear force which keep protons tied to other protons or neutrons is mediated not by gluons but by maison. Electromagnetism shapes light and chemistry. The weak force governs radioactive decay and particle transformation. The strong force binds the core of matter itself. Together, these forces form the quantum foundation of the universe and explain why atoms, matter, and the world around us can exist at all. I'll see you in the next video, my friend.