Frank Close delves into fundamental particles and forces to find clues to a deep unsolved mystery of physics: why is matter neutral? 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...