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Fundamental Particles: Definition, Principles & Examples

Instructor: Lori Jones

Lori has a degree from Stanford, was Principal of a K-12 private school that she started, has a Master's degree, and taught at the high school level.

Fundamental particles make up and operate everything in our universe. In this lesson, we will cover what fundamental particles are, and take a look at the different types, characteristics, and groupings.

Fundamental Particles

General Particle Image

In the 2016 movie Ant Man, the title character's suit helped him shrink to the size of an ant. Toward the end of the movie, his character shrank so small that he entered what the movie called the ''quantum realm.'' He shrank to such a minuscule size that he became smaller than the smallest particles known to man, as he began to ''shrink for all eternity.'' While the movie didn't go into details, we did get a glimpse of just how small the particles that make up our universe can be.

When thinking about particles, most of us are familiar with the electron, proton, and neutron. But did you know that there are dozens of other particles and particle combinations out there? What exactly are these particles? Let's dive a little deeper.

Types of Fundamental Particles

Fundamental particles (also called elementary particles) are the smallest building blocks of the universe. The key characteristic of fundamental particles is that they have no internal structure. In other words, they are not made up of anything else. There are two types of fundamental particles:

  1. Particles that make up all matter, called fermions
  2. Particles that carry force, called bosons

One might argue that science wouldn't be science without its various groups, subgroups, types, subtypes, classifications and combinations. Particle physics is no exception, as fundamental particles actually come in several types and combine to form other particles. Let's take a deeper look at the types, groups, and combinations of fundamental particles.

Fermions

All matter (including you and me) is made up of fermions, and these fermions come in two types: leptons and quarks.

Leptons

Leptons are fermions and are considered solitary particles. They operate alone and do not form groups. Leptons come in 6 different varieties called flavors. (Although, it probably wouldn't taste like anything if you ate one.) Like all fundamental particles, they have no internal structure. The six flavors of leptons are

  1. Electron
  2. Electron Neutrino
  3. Muon
  4. Muon Neutrino
  5. Tau
  6. Tau Neutrino

Listed in order of their mass from lightest to heaviest, the electron and electron neutrino have the least mass of all six, and the tau and tau neutrino are the heaviest of the group.

Lepton Charges

Leptons carry a negative or neutral charge known as an integer charge. (Their charge is a whole number, or integer.)

  • The electron, muon, and tau all carry a negative (-1) charge
  • The neutrinos carry a neutral (0) charge

Quarks

Not to be outdone by leptons, quarks (the other type of fermion) also come in 6 different flavors with some of the craziest names found in particle physics. The six flavors of quarks are: 

  1. Up
  2. Down
  3. Charm
  4. Strange
  5. Top
  6. Bottom

Quarks are also listed in order of their mass from lightest to heaviest. The Up Quark has the lightest mass of the group, and the appropriately named Bottom Quark is the heaviest.

Standard Model of Fundamental Particles
Table of Fundamental Particles

Quark Charges

To further distinguish themselves from leptons, quarks don't carry the same full charge that electrons do. They carry a positive or negative fractional charge, which is a fraction of the charge of an electron's integer charge.

  • Up, Charm, and Top carry a 2/3 positive charge
  • Down, Strange, and Bottom carry -1/3 negative charge

All quarks and leptons have oppositely-charged particles called antiparticles. For example, you can have a charm antiquark, an anti-electron (called a positron), and an anti-neutrino.

As we mentioned previously, leptons are solitary particles; they like to be by themselves. Quarks, on the other hand, are very social and are only found in groups. So they combine to form composite particles.

Because composite particles are combinations of other particles, they are not considered fundamental particles.

Composite Particles

Composite particles are particles that are made up of more than one quark, and like other particles in physics, they have a name. These are called hadrons and come in two different classes:

  1. Mesons - hadrons that are made up of 2 quarks (1 quark and 1 antiquark)
  2. Baryons - hadrons that are made up of 3 quarks

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