What is an electron? If you asked a physicist, you wouldn't hear about colour, or texture, or even shape. You would hear about an equation — in particular, the Dirac equation, a piece of mathematics that explains, with incredible accuracy, the behaviour of particles. And according to Roger Penrose, the Dirac equation is just one reason why we might suspect that the world itself is mathematical. Because the philosophical question is whether maths is just a language we have invented, or whether it

Electrons Are Not What You Think