Add Yahoo as a preferred source to see more of our stories on Google. When you buy through links on our articles, Future and its syndication partners may earn a commission. The particles that are in ...

Every time I write about particle physics, I encounter a moment of uncertainty about a quantity that, at first glance, ought to be clear. How many kinds of elementary particles should I say there are?

The particles that are in an atom: protons, neutrons and electrons The particles that are in protons and neutrons: quarks The four fundamental forces: gravity, electromagnetism, the strong force and ...