Basically, it collides particles at an extremely insane amount of velocity so that scientists will hopefully be able to provide new theories on the principles of matter. Proponents of the project (which takes place over several miles near Swiss and French borders on the outskirts of Geneva) say that the LHC (also lovingly called "The Big Banger," "Masta Blasta" and "Colossitron") is the means by which we'll be able to better understand the universe around us and our interrelationship with it.
From UK's The Guardian:
"Particle physics is the unbelievable in pursuit of the unimaginable. To pinpoint the smallest fragments of the universe you have to build the biggest machine in the world. To recreate the first millionths of a second of creation you have to focus energy on an awesome scale."
Sounds dreamy, eh? Well, all of the technical details aside, there are definitely two camps on this galactically-important subject: those who think colliding particles is the key to understanding our universe, and those who think the damned thing is going to create an uncontrollable black hole right here on Earth that will consume everything in its path and end life as we know it.
So far, no evidence has been found to support the world-ending theory of some, but those folks are getting their day: the LHC will be shut down for at least 12 months starting in approximately 2012. Apparently, some flaws in the design of the LHC have been found that could, given the right conditions, destroy the machine itself if allowed to crash shit together at full-power.
According to The Independent UK:
"Scientists in charge of the Large Hadron Collider (LHC) in Geneva announced yesterday that the machine will only be able to run on half energy before it is temporarily shut down in two years' time. Its full operating capacity designed to probe the frontiers of science will not be achieved until at least 2013 – several years later than planned."
I don't know about you, but when a machine that big is throwing particles around at greater-than-light speeds and the scientists say it can destroy itself if allowed to run at full power, I think they made the right choice to go at half-impulse for the remainder of the time until it's repaired...