Human beings have long been aware of the electric and magnetic forces around us, from the electrostatic charge built up by rubbing amber with fur, to the pull of the lodestone, 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 part of the 20th 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. And that enables the much weaker force of gravity - always attractive - to dominate at large scales, building planets, stars, and galaxies. Things would have been very different, had the charges not cancelled.

As far as we know, the charges of the proton and electron are opposite and exactly equal, even though the proton is far bigger, and composed of three quarks tightly bound within it, while the electron is a fundamental particle. But why are they equal? This is one of the deepest unresolved puzzles of fundamental physics, and forms the driving force of this book. To explore the clues we have, 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 at these short ranges, and the colour and flavour charges that drive them, as well as the parallels between them, giving tantalizing hints of a deeper unity of all forces that is the dream of grand unification theories. Seeking an answer to why matter is neutral brings us to fundamental forces and particles, the Standard Model, the recently discovered Higgs boson, and the implications of grand unification for the stability of matter. Within this compact volume, Close packs in an extraordinarily rich account of our current understanding and the efforts of the latest ambitious experiments to probe further, and test theoretical possibilities such as the decay of protons.