Why LHC

Why do we need the LHC?
Because our current understanding of the Universe is incomplete.

The theories and discoveries of thousands of physicists over the past century have created a remarkable picture of the fundamental structure of matter, which is called the Standard Model of Particles and Forces. The Standard Model is by now a well-tested physics theory, used to explain and exactly predict a vast variety of phenomena. High-precision experiments have repeatedly verified subtle predicted effects. Nevertheless, physicists know that it can't be the end of the story, as it leaves many unsolved questions.

Among them, the reason why elementary particles have mass, and why their are different, is the most perplexing one. It is remarkable that such a familiar concept is so poorly understood! The answer may lie within the Standard Model, in an idea called the Higgs mechanism. According to this, the whole of space is filled with a 'Higgs field', and by interacting with this field, particles acquire their masses. Particles which interact strongly with the Higgs field are heavy, whilst those which interact weakly are light. The Higgs field has at least one new particle associated with it, the Higgs boson. If such particle exists, the LHC will be able to make it detectable.

Another puzzle concerns the existence of four different forces. When the Universe was young and much hotter than today, perhaps these forces all behaved as one. Particle physicists hope to find a single theoretical framework to prove this, and have already had some success. Two forces, the electromagnetic force and the weak force were 'unified' into a single theory in the 1970s. This theory was experimentally verified in a Nobel prize winning experiment at CERN a few years later. The weakest and the strongest forces, however, gravity and the strong force, remain apart. A very popular idea suggested by the unification of the forces is called supersymmetry or SUSY for short. SUSY predicts that for each known particle there is a 'supersymmetric' partner. If SUSY is right, then supersymmetric particles should be found at the LHC.

Antimatter poses another riddle the LHC will help us also to solve the riddle of antimatter. It was once thought that antimatter was a perfect 'reflection' of matter - that if you replaced matter with antimatter and looked at the result in a mirror, you would not be able to tell the difference. We now know that the reflection is imperfect, and this could have led to the matter-antimatter imbalance. The LHC will be a very good 'antimatter-mirror', allowing us to put the Standard Model through one of its most grueling tests yet.

These are just a few of the questions the LHC should answer, but history has shown that the greatest advances in science are often unexpected. Although we have a good idea of what we hope to find at the LHC, nature may well have surprises in store.

One thing is certain, the LHC will change our view of the Universe.