The Four Fundamental Forces

If you’ve ever seen Star Wars, you may know that there is an energy called the Force which surrounds everything in that universe. In kind of a similar way, our universe is also surrounded by force – in fact, ours has four of them. They are called the four fundamental forces, and they are basically what allows all things to move around and interact with each other. In fact, just like the Jedis who use the Force, you interact with the four fundamental forces every day! You just do so in different ways.

What are the four forces?

The diagram below shows the four fundamental forces and their basic roles in the universe. What is fascinating is that nearly every event in our universe – from the movement of an atom to the explosion of a sun – can be explained through these four forces. They are electromagnetism, weak nuclear, strong nuclear, and gravity. Below each force, you will see a particle in a blue box. These are certain types of elementary particles called carrier particles. What this means is they carry the fundamental forces. Whenever objects interact with each other, these carrier particles are passed between them, thus allowing one of the four forces to then interact between the objects. You’ll notice that the carrier particle for gravity has a question mark. That’s because we still haven’t found it!

Strong nuclear forces

Let’s begin with the strong nuclear force, the strongest of the four forces. The diagram above shows a group of protons (the circles with a P) and neutrons (the circles with an N)

bunched together in a nucleus. The strong nuclear force is what keeps the protons and neutrons bound together in a nucleus. In this case, gluons are the carrier particles for the strong nuclear force. Gluons are the glue that keeps protons and neutrons together! If we zoom all the way into an atom, we will see protons and neutrons clumped together in a nucleus.

And if we zoom farther into one of these protons or neutrons, as we see in the purple diagram above, we will find quarks. Quarks are really tiny particles that makeup protons and neutrons. And surrounding these quarks are – wouldn’t you know – gluons! Gluons keep quarks together with their strong nuclear force, thus keeping protons and neutrons together in an atom’s nucleus. And because you are made up of atoms, you experience the strong nuclear force every second of the day!

Electromagnetism

Next up, electromagnetism, or the electromagnetic force. This is what’s responsible for our vision and all the interactions between the atoms in our world. How? Well, when we look at something, our eyes are actually capturing billions of tiny little particles called photons which radiate from the thing we are looking at.

The photons of a tree you are looking at go into your eye and hit the retina. This causes electrical signals to travel down the optic nerve, which enters your brain. Once in your brain, these signals form an image of the tree!

Photons are the carrier particle for electromagnetic force. These photons hit a part of our eye called the retina, which causes electric signals to be sent to our brain. Once in our brain, these signals form a picture of the object we are looking at. Photons and their electromagnetic force also cause electrons to orbit around the nuclei of atoms. Since electrons are responsible for bonding atoms together, the electromagnetic force is what allows for all the interactions between atoms in our world! For example, when you digest food, the electrons around the atoms of the food you just ate are bonding to other atoms, allowing all the nutrients to be broken down into energy. You can thank photons and the electromagnetic force for that!

Here is an illustration of electrons causing atoms to bond together. In this case, the electrons from two hydrogen atoms are binding to an oxygen atom, creating H2O, or water. Bonds like this are happening all the time in nature and in your body!

Weak nuclear force

Next up, the weak nuclear force, which is carried by the W and Z bosons and which is responsible for beta decay.

Well, that was a mouthful – let’s break down what all these terms mean. First of all, W and Z bosons are the carrier particles of the weak nuclear force. Beta decay, which is caused by the weak nuclear force, is what happens when a beta particle, or high energy proton or neutron, is ejected from an atom’s nucleus. Here, the weak nuclear force causes this beta particle to be ejected. Beta decay happens all the time in our universe. For example, the sun allows for hydrogen atoms to be fused together which releases a ton of energy.

This energy powers all the life on Earth, including you!

Gravity

Finally, we come to gravity, the weakest of the four fundamental forces. While scientists have discovered carrier particles for the three forces we’ve explored so far, one for gravity still hasn’t been found yet. If we were to find it, we’d call it a gravitron.

What does gravity do? Well, it’s what keeps us on Earth, what keeps Earth and all the other planets orbiting around the sun, and what keeps the sun and our solar system moving through the milky way. In fact, what’s interesting about gravity is that it’s caused when an object bends space. Yes, you read that correctly –bends space. Everything that has mass basically warps space around it like a funnel. For example, the space that the sun bends causes the Earth to orbit around it. You can think of the Earth as sort of rolling around this curved space like a ball. It’s thought that if gravitrons exist, they’d be the ones helping to do this bending.

Believe it or not, you curve space too! The reason why you don’t see anything orbiting around you or falling towards you in your daily life is that you don’t have a lot of mass. Only objects with a ton of mass, like the sun and the planets, can produce the large amounts of gravity needed to make other objects orbit around them.

Here are two animations of how gravity works. The one on the right shows how the sun bends space, causing the Earth to orbit around it. The one on the left also shows how objects bend space, but more realistically. It would be confusing to do an animation of the Earth orbiting the sun with space being bent like this, so it is very common to see animations like the one on the right.

That concludes our tour of the four fundamental forces. While these forces and their carrier particles are invisible to you, remember that, whenever you watch an epic movie (electromagnetism), catch a falling ball (gravity) or feel the warmth of the sun on your face (weak nuclear force), these forces are always a part of your life.