It was clear by the 1950s just how important the weak force is. However, its exact nature remained a mystery. There were tentative indications that it might be possible to unify electromagnetism and the weak force and describe them within a single theory of a combined electroweak force. But a vital ingredient was missing. How could both forces be different manifestations of a single force if one, the electromagnetic force, was a powerful long range force, whereas the other was a very weak force that only operated over length scales that are smaller than an atomic nucleus? In this chapter, we will see how this paradox was resolved. The answer came through the understanding of a subtle physical effect known as spontaneous symmetry breaking.

Half a century passed between the discovery of superconductivity and an explanation of its origin in terms of particle interactions. A British physicist Peter Higgs realised how a similar mechanism might be responsible for breaking the symmetries of the fundamental forces of Nature. His model was developed into a unified theory of the electroweak force by the American theorist Steven Weinberg. One of the predictions of this theory is the existence of a heavy particle that has become known as the Higgs. The quest for the Higgs is one of the main motivations for the construction of the world’s most powerful particle accelerator, the Large Hadron Collider at CERN.