Elementary particle physics addresses the question, “What is matter made of?” on the most fundamental level – which is to say, on the smallest scale of size.

It's a remarkable fact that matter, at this scale, comes in tiny chunks, separated by vast empty spaces. This is radically different from our everyday experience, where matter appears to fill everything. Solids seem … well … solid, liquids are smooth and continuous, and even gases, such as the air in a room, occupy every nook and cranny. But the world of the very small is much more like the night sky, with pinpoints of light here and there, but mostly just nothing.

Even more surprising, these “chunks” come in a relatively small number of different types – there are protons and electrons, pi mesons and neutrinos, … only a few dozen in all. Again, this is totally different from our macroscopic world, where there are rocks and dirt clods, bananas and chimpanzees, trees, books, and people – variety without limit.

Most astonishing of all, the chunks of any particular type are not just “pretty similar,” like two Fords coming off the same assembly line, but absolutely utterly identical. There aren't fat electrons and skinny ones, or young electrons and old electrons, or happy electrons and sad electrons – if you've seen one, you've seen them all. There is nothing remotely like this absolute identicalness in everyday life – it is a quantum phenomenon, inconceivable in classical physics, where you could always, if necessary, paint a red spot on the object, or stamp a serial number on it.