Everything around us – from life on Earth, to the stars themselves – is made of atoms. The word “atom” means “indivisible” because scientists used to believe that nothing was smaller than an atom. But the world is much stranger than that!
Atoms are made of three kinds of “subatomic” particles:
Electrons: particles with a negative electrical charge
Neutrons, which have a neutral charge
Protons: positively-charged particles
At the heart of the atom is its nucleus, which contains protons and neutrons. The electrons whiz in orbit around the nucleus. But we can never know with certainty where they are exactly and how fast they are moving.
These particles also each have a twin made of antimatter. The twins are exactly the same except for one thing: the “antiparticles” have an opposite charge.
But are subatomic particles made of anything? As it turns out, yes: quarks. These tiny objects are so miniscule they may just be points in space. An odd thing about quarks is they have fractional electric charges; this is in contrast with the other particles, which have charges of 1 or -1. Quarks, which are usually discussed in pairs, have whimsical names:
- Up/down: These two quarks have (2/3) and (-1/3) charge respectively
- Charm/strange: (2/3) and (-1/3)
- Top/bottom: (2/3) and (-1/3)
The 6 types of quarks are called “flavors.” Yes, that is the technical name for the kinds of quarks!
Quarks, too, have antimatter twins. These “antiquarks” have an opposite electrical charge. For example, an anti-strange quark has a charge of -(-1/3) or simply (1/3), and an anti-top quark has a charge of –(2/3).
Quarks never appear in isolation. They are social and can be found in “composite particles” with other quarks, so that the sum of the charge equals a non-fraction [an “integer”]. Composite particles made of quarks are called hadrons. There are two kinds of hadrons:
- Baryons: made of 3 quarks. Protons are baryons. They are made from 2 up quarks and 1 down quark: (2/3) + (2/3) + (-1/3) = (3/3) or 1. Neutrons are also baryons. They are made from 2 down quarks and 1 up quark: (-1/3)+ (-1/3) + (2/3) = 0 [a neutral charge]
- Mesons: contain 1 quark and 1 antiquark. Because mesons consist of matter and antimatter, they are extremely unstable and don’t typically live very long.
You may have noticed that I didn’t describe electrons as being made of quarks. That’s because they are not. Electrons belong to a different type of matter called leptons. There are 6 leptons; 3 have an electric charge and 3 do not. Like quarks, they appear to be tiny points without any internal structure. The types of leptons are:
- Electrons: negative charge
- Muon: positive charge
- Tau: charged like an electron [negatively], the tau has a lot more mass
- And 3 types of neutrinos: these are strange beasts because they have an extremely light mass, no electrical charge, and are difficult to find.
Whereas quarks are social, leptons are loners and are usually not found in groups. [Remember that electrons can be found circling above an atom’s nucleus.] But, like all other particles, leptons too have antimatter twins. “Anti-electron” is a mouthful; the electron’s antiparticle is called a positron.
Are quarks made of anything? As of yet, it appears not. But some physicists propose that all matter – even supposedly “fundamental” particles like leptons and quarks – are made of something tinier still: strings. These vibrating rings of energy are so small, we can’t see or even detect them. But only further experiments will reveal the truth about this lilliputian realm.