The quantum world: A concise guide to the particles that make reality

The ancient Greeks speculated that it might be air, fire or water. A century ago, physicists felt sure it was the atom. Today, we believe that the deepest layer of reality is populated by a diverse cast of elementary particles, all governed by quantum theory. From this invisible, infinitesimal realm, everything we see and experience emerges. It is a world full of wonder, yet it can be mystifying in its weirdness. Or at least it can often feel that way.

What you’ll find below is a concise, clear-eyed guide to the known particles and forces – from electrons, quarks, and neutrinos to photons and the Higgs boson – as well as the quantum laws and phenomena that give quantum physics its reputation for strangeness, including wave-particle duality, entanglement, and the uncertainty principle. You will also discover the hypothetical particles that could make sense of cosmological conundrums such as dark matter and dark energy, and the stranger things that might lurk beneath the quantum realm. Finally, you will have many of your questions answered, not least what is a theory of everything anyway?

MATTER

We start with what we pretty much know for sure. Visible matter consists of atoms, and at the centre of atoms are protons and neutrons. But even these aren’t elementary particles, as detailed by the current “standard model” of particle physics, our leading description of reality on the tiniest scales. So we begin, deep down, with what matter is really made of.