One hundred metres beneath the Geneva countryside, the final touches are being made to the world's largest piece of scientific equipment: the Large Hadron Collider (LHC) which will start operating later this year. The LHC is the most powerful particle accelerator - or atom smasher - ever built. It is capable of producing fundamental particles last seen a billionth of a second after the big bang, for a tiny instant of time. And it is capable of doing so not just once, but 40 million times a second, 24 hours a day.

Why would we want to do this? Well, it helps us understand what the universe is made of - in fact to understand what matter (all the "stuff" in the universe) itself is made of. You might already know that everything is made of atoms. Our search is for the ingredients of atoms: particles as small compared to an atom as an atom is compared to you. Our search is for the fundamental particles that populated the universe just after the big bang, before the universe had time to cool and join them up into not just atoms but stars, galaxies and, ultimately, us!

So far we've found that all matter in the universe is made of 12 types of matter particles (such as the one on the left) held together by four different types of forces. Despite many successes, the theory describing particle physics doesn't explain many of the fundamental features of matter. For example, at the moment we have no idea why there should be exactly 12 fundamental particles, or indeed how gravity fits in to the whole picture.

Even more worryingly, we have only been able to study the observable universe, which is a paltry 4 per cent of the entire thing. Some 23 per cent of the universe is made of mysterious "dark matter", whose presence is inferred from studying the effects of gravity on galaxies (see page 14). The rest is made of even stranger "dark energy", which is thought to be responsible for the acceleration of the universe.

The only way to solve these mysteries is by experiment. The LHC will accelerate two separated, counter-circulating beams of protons to almost light speed. When these beams have reached target energy, their path is altered to bring them into collision at four points around the 27km-long circular ring. Experiments have been built around these points to detect as many of the particles streaming out from a collision as possible. By analysing the electronic snapshots taken by the experiments we can infer what fundamental particles were originally produced in a collision, and how they behaved. If we see a new particle, or some strange behaviour that we don't understand, we could be on the way to answering some of our biggest mysteries.

The LHC and its experiments are so large that it has taken over 20 years to design and build them. Excavating the tunnel (above) used to house the LHC was Europe's second largest civil engineering project. The ATLAS experiment (below) is the size of a five-storey building, yet it contains detectors that can reconstruct the position of a particle passing through them to the precision of a tenth of a human hair's thickness.

It's not just the equipment that's huge: some 6,000 particle physicists from all over the world participate in the experiments. We have even had to invent new ways of computing to ensure we're able to analyse the data. Now, with LHC start-up imminent, we're finally confident that all the pieces are in place to allow us to study what we've never looked at before.

What will we find when the LHC reaches its highest energies in 2008? We have some ideas about what we might see based on our previous experiments, but anything is possible! We've never looked so deeply into the heart of matter before and that's what makes the whole adventure so incredibly interesting. Stay tuned, the beginning of the universe is on its way...

Tara Shears is a Royal Society university research fellow at the University of Liverpool


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