A major breakthrough in particle physics came in the 1970s when physicists realized that there are very close ties between two of the four fundamental forces – namely, the weak force and the electromagnetic force. The two forces can be described within the same theory, which forms the basis of the Standard Model. This ‘unification’ implies that electricity, magnetism, light and some types of radioactivity are all manifestations of a single underlying force called, unsurprisingly, the electroweak force. But in order for this unification to work mathematically, it requires that the force-carrying particles have no mass. We know from experiments that this is not true, so physicists Peter Higgs, Robert Brout and François Englert came up with a solution to solve this conundrum.
They suggested that all particles had no mass just after the Big Bang. As the Universe cooled and the temperature fell below a critical value, an invisible force field called the ‘Higgs field’ was formed together with the associated ‘Higgs boson’. The field prevails throughout the cosmos: any particles that interact with it are given a mass via the Higgs boson. The more they interact, the heavier they become, whereas particles that never interact are left with no mass at all.
This idea provided a satisfactory solution and fitted well with established theories and phenomena. The problem is that no one has ever observed the Higgs boson in an experiment to confirm the theory. Finding this particle would give an insight into why particles have certain mass, and help to develop subsequent physics. The technical problem is that we do not know the mass of the Higgs boson itself, which makes it more difficult to identify. Physicists have to look for it by systematically searching a range of mass within which it is predicted to exist. The yet unexplored range is accessible using the Large Hadron Collider, which will decide the existence of the Higgs boson. If it turns out that we cannot find it, this will leave the field wide open for physicists to develop a completely new theory to explain the origin of particle mass.