The LHC will blast protons - one of the building blocks of atoms - at a velocity close to the speed of light, generating temperatures of more than a trillion degrees centigrade. Each proton beam will pack as much energy as a Eurostar train travelling at 150 kilometres per hour. The resulting collisions will hopefully replicate conditions found in the moments following the Big Bang - or the beginning of the universe - and scientists will study the fallout. Let's just hope nothing goes wrong!
And if you're worried that man's meddling is going to create a black hole under the Alps which will suck the Earth into it, then have a look at this to help calm your nerves.