Since Emp. Peng. pointed the internet to me as the Rookery's resident expert on the Large Hadron Collider (and I would like to point out that, outside the Rookery, I am not much of an expert on the topic), I figured I should provide the rundown of the reasons that the LHC will not annihilate the planet. Actually, I will provide
a link to an actual astronomer who has actually gone to the LHC, explaining why the LHC will not annihilate the planet.
And a link to his followup post. While I am at it, I'll give a tip o' the beak to Phil Plait, my favorite blogger to whom I am not married. He has a marvelous way of making physics and astronomy comprehensible to those of us who decided not to take calculus.
There are two main reasons some people think the LHC may obliterate the planet. First, the collider may create little black holes, and having one of those on Earth is probably not a good idea, as far as the continued existence of the planet goes. For the second potential doomsday scenario, the collider might create theoretical particles called strangelets, and if too many strangelets get together, it will be like the Tribble episode of Star Trek, except that instead of William Shatner getting buried by Space Gerbils, all matter in the vicinity--including William Shatner, us, and any space- or Earth-based gerbils--gets converted into theoretical particles. Neither one of these is a cause for concern, though. The folks running the LHC, who would be right in the thick of any annihilation, aren't worried about it, and they understand the math behind why they are not. Since I do not understand the math, I will defer to them. The non-math-intensive reasons they are not concerned:
1. The physics that would allow for the creation of black holes in the LHC also require that the black holes evaporate. The physics that would allow for a black hole to not evaporate instantly do not allow for the creation of black holes under the circumstances that the LHC will provide. Either we get black holes that go poof! or no black holes at all. Whichever way it ends up, we are pretty much safe from finding out firsthand what spaghettification feels like. And, yes, "spaghettification" is the technical term for what happens when you are subjected to a massive gravity fields and your feet get attracted to the gravity well faster than your head.
2. No one is entirely certain strangelets are real. In the event that they are real, better circumstances than the LHC for creating them exist naturally on the Moon. Since the Moon has not been converted into Theoretical Space Gerbil Particles, odds are we won't be either when the LHC gets up to speed.