I’ll lead with an apology: I got ambitious. You said you wanted to know about particles; I wanted to say a lot about them, so I guess I wrote a book.

Also a disclaimer: I only had physics through undergrad. My source is Sections 1 through 3.1 in Baez, J., & Huerta, J. (2010). The Algebra of Grand Unified Theories. Bulletin of the American Mathematical Society, 47(3), 483–552. if you want to consult something more reliable.

Introduction

If you look inside a bakery, you will find lots of different ingredients—flour, sugar, butter, milk, eggs, and so on. By combining these ingredients in different ways, the baker can make all kinds of different breads and desserts. To make the kind of food they want, the baker has to understand their ingredients, how much of each kind to use, and how to combine them.

In the same way, we know that everything in the world can be made out of different kinds of very tiny ingredients called elementary particles. By combining these particles in different ways, we can create all kinds of stuff. But to make the stuff we want, we have to understand the elementary particles and how they affect each other, just like the baker has to understand their ingredients and how they go together.

There are over one hundred different kinds of elementary particles that we know about and maybe more that we don’t. We could just memorize them all, but scientists think it’s better to look for patterns. Think about when you were learning addition: its easier to learn that zero plus anything is always the same thing than it is to memorize 0 + 0 = 0, 0 + 1 = 1, 0 + 2 = 2, 0 + 3 = 3, and so on. Scientists do the same thing; they find patterns. Eventually they wrote down all of the elementary particles that they had discovered and all of the patterns they were really sure about. They called this knowledge “The Standard Model”.

The particles are fairly easy:

There’s two basic categories of fundamental particle, fermions and bosons, based on what kind of spin they have. Spin in quantum mechanics is a fundamental property; there’s no way to stop an electron (for example) from spinning or to give it more spin. Fermions have half-odd-integer spin and so obey Fermi-Dirac statistics, which means there can’t be more than one of them in a given quantum state. Bosons have integer spin and so obey Bose-Einstein statistics, which means they can bunch up in quantum states. This leads to electrons, which are fermions, separating themselves into separate electron shells, which results in the solid matter we know and love, and bosonic atoms like rubidium being able to form a Bose-Einstein condensate, which has a lot of interesting properties.

Fermions are divided into quarks and leptons, where quarks are fermions that do participate in the strong interaction and leptons are fermions which do not. There’s three generations of each; the quark generations go up and down, strange and charm, and top and bottom, with each generation more massive, and therefore more short-lived, than the previous. All matter you’ve ever directly experienced is made of up and down quarks, which combine to form protons and neutrons in atomic nuclei, using gluons to mediate the strong force. Leptons may be charged or uncharged, by which I mean electrical charge, and also come in three generations named after the charged “electron-like” lepton of that generation, those being electrons, muons, and tauons. Each of those charged leptons has a charge of -1, and, again, each generation is more massive and shorter-lived than the previous. The neutral leptons are the neutrinos, which only participate in the weak interaction and gravity and, therefore, barely interact with other matter at all. Huge volumes of neutrinos from the Sun ghost right through Earth completely unchanged, night and day. Yes, we have solar neutrinos shining up through the ground on us at night. The neutrinos, while they do come in three generations (electron neutrinos, muon neutrinos, and tau neutrinos), have a very poorly-understood mass; while it cannot be zero, we don’t know what it is, only that it’s very small, and beneath some threshold value which gets revised downwards every so often.

Bosons are force carriers, and divided into two categories based on mathematical properties beyond even this post. The gauge bosons, all with spin 1, are the photon, which carries the electromagnetic force, the W and Z bosons, which carry the weak force, and eight gluons, which carry the strong force. The only scalar boson, with spin 0, is the Higgs boson, which is one of the things that helps give matter mass.

Particles have antiparticles, which have equal and opposite charges (electromagnetic, weak, and so on) to their opposite number. For example, the electron’s antiparticle, called the positron, has an electromagnetic charge of +1. Even neutrinos have antiparticles, which helps balance the books as regards something called lepton number. However, some truly neutral particles, such as the photon, the Z boson, and the Higgs boson, are their own antiparticles.

In physics, a particle is a fundamental or elementary unit of matter or energy. It refers to a localized object that exhibits certain properties, such as mass, charge, and spin.

The standard model of quantum physics is like a special chart that helps scientists understand and organize all particles. It tells us that there are two main categories of particles: matter particles and force particles.

Matter particles are the ones that make up things like you, me, and everything we see. They are further divided into two groups: quarks and leptons.

• Quarks are like the tiniest building blocks of matter, and they come in different types called flavors, such as up, down, charm, strange, top, and bottom. They can be combined together to form “composite particles” like protons or neutrons.

• Leptons include particles like neutrinos which have no electrical charge, or electrons which are found in atoms, and they have a negative charge.

The other category is force particles, also called bosons.

These particles are responsible for carrying forces between matter particles. They help things stick together or repel each other. The force particles include the photon, which carries electromagnetic energy (they form light), the W and Z bosons, which help with the weak nuclear force and gluons that mediate the strong nuclear force by interacting with quarks.