Humans have long been aware of the electric and magnetic forces around us, and scientific investigation showed that the two are intimately connected as electromagnetism. Lightning shows how devastating electricity can be in nature, while humans learned to exploit the flow of negatively charged electrons that make up an electric current. In the early twentieth century, the experiments of Ernest Rutherford showed that at the heart of atoms lies a positively charged nucleus. The positive charge comes from protons. Atoms are neutral because the charges of the electron and proton cancel out.

The charges of the proton and electron are opposite and equal, even though the proton is bigger. But why are they equal? This is one of the deepest unresolved puzzles of physics. Frank Close takes us on a journey into the quantum subatomic world of particles. He describes the strong and weak forces that operate alongside electromagnetism, the color and flavor charges, as well as the parallels between them, giving hints of a deeper unity. Seeking an answer to why matter is neutral brings us to fundamental forces and particles, the Standard Model, the Higgs boson, and implications of grand unification for the stability of matter. Close packs in a rich account of our current understanding and the latest ambitious experiments to probe further, and test theoretical possibilities.