Its business is fundamental physics, finding out what the Universe is made of and how it works. At CERN, the world’s largest and most complex scientific instruments are used to study the basic constituents of matter — the fundamental particles. By studying what happens when these particles collide, physicists learn about the laws of Nature. The instruments used at CERN are particle accelerators and detectors. Accelerators boost beams of particles to high energies before they are made to collide with each other or with stationary targets. Detectors observe and record the results of these collisions.

In short, new stuff! Did you know that without particle accelerators, as at CERN, quantum mechanics would almost certainly never have been invented, and without quantum mechanics, transistors would almost certainly not have been invented, and without transistors, there would be no PCs and none of us would know you asked the question?!! The fundamental theories of physics are "almost finished". Everything you learn about physics in school can be shown to be a consquence of the "Standard Model of Particle Physics" following the laws of Quantum Mechanics OR a consequence of Einstein's theory of General Relativity. General Relativity describes gravity and works accurately for really large objects like planets. Quantum Mechanics works incredibly accurately for tiny particles inside atoms. Unfortunately the two theories actually contradict each other. They cannot both be right. There must be some scheme which incorporates aspects of both GR and QM. There are various theories which can do this, but experiments need to be done to find out what is really true. Something the LHC will defintely decide upon is the Higgs Boson: The Standard Model has an unfortunate flaw. It predicts the mass of all the particles is zero. This can't be right. The Higgs mechanism explains how particles might gain mass. It requires a new particle called the Higgs Boson. If it exists, LHC will find it. If the Higgs Boson is found, physicists rejoice - the theory that has been used for so many decades is right! But if the Higgs is not found, scientists will be agog with wonder! The Standard Model is WRONG! Everyone will be scrambling to come up with some new theory which explains things as well as the Standard Model. The good thing about all this stuff, is that understanding the world in more detail allows us to create things we could never have created without that knowledge. Things that can revolutionize the planet. Did you know the World Wide Web was invented at CERN? It was invented as a way to organize the reports that were being generated there, so that scientists could easily click to where they watned to go.