What Are Subatomic Particles?

Question posed by Amy.

Atoms are the basic building blocks of all the elements in the periodic table, that come together to make everything we can see and interact with in the world around us. In around 450 BCE, Ancient Greek philosopher Democritus first used the term "átomos," which means "uncuttable," implying that atoms were the smallest particles of matter and could not be broken down into smaller particles.

He was wrong.


The Short Answer

Subatomic particles are particles that are smaller than atoms (hence "sub-atomic," where 'sub-' means 'below' or 'under'). Where atoms are the basic building blocks of matter, subatomic particles are the basic building blocks of atoms themselves.


The Quite A Bit Longer Answer That Builds On The Short Answer

There are two types of subatomic particles: elementary particles and composite particles. Both types are studied by the Particle Physics and Nuclear Physics fields of science. I'm going to type the names of some of them below, but first I'd like to ensure you that however weird these names look to you, you're not alone in thinking so! Some of the naming conventions are attempts to describe and label properties which are completely alien to us at the scales of existence that we're used to; others are particle physicist in-jokes which would be long and laborious to explain, and wouldn't raise so much as a giggle from most normal people anyway.

By MissMJ [CC-BY-3.0)], via Wikimedia Commons.
This can be thought of as a 'periodic table' for
the elementary particles.

Elementary Particles
In the Standard Model of particle physics, there are three categories of elementary particle:

• Quarks: These are divided into six 'flavours': up, down, bottom, top, strange and charm (see what I mean about the names?)
• Leptons: There are six different types of these, too: electrons (you know these!), electron neutrinos, muons, muon neutrinos, taus* and tau neutrinos.
• Gauge bosons: These are 'force carriers', and there are thirteen types: gravitons ('carrying' gravity), photons (electromagnetism), W⁺, W^- and Z bosons (all carriers of the 'weak force'), and eight types (known as 'colours') of gluon (carrying the 'strong force').

Composite Particles

Composite particles are simply** particles made up of two or more elementary particles. Protons, for example, are made from three quarks (two ups and one down). When elementary particles come together to make composite particles, they are said to be in a 'bound state'. Another particle you've probably heard of, the neutron, is a bound state of one up-quark and two down-quarks.

I think I'll stop there.

* "Tau" is prounounced like "ow" (as if someone thumps your arm) with a "T" on the front.

** Inasmuch as anything can be 'simple' in particle physics.