At this point almost everybody knows what LHC is. There is more than enough media hype around it, and especially around its "danger to the whole planet". There is even a lawsuit about it already... While it is nice that people who are far from science are interested in this topic, it is a bit annoying when people try to give advice without even understanding the subject they are speaking about. Unfortunately, this is exactly the case with the LHC.
According to the media, there are two ways in which LHC can destroy our planet: by creating micro black holes (that would tear the planet apart) or by creating a so called "strange matter" capable of converting our planet into a "strange star". I am not going to attack the people who are behind this ideas, but I do think that this ideas don't have a sufficient logical basis.
Lets examine both of the ideas.
Micro black holes: It is not yet even an accepted theory that they may be created in the conditions provided by LHC. It would be wrong to disregard it because of this, but even if such holes will indeed form there is no reason to be afraid from them.
Black holes are dangerous because of their gravitational pull. This pull is so strong that even light cannot escape the event horizon of a black hole. But why black holes have such a strong gravitational pull? In order to have gravity you need mass, the bigger the mass the more force you will get. The cosmic black holes we often hear about have the mass of at least 3 suns (this is the theoretical minimum, usually they are much large). LHC is not capable of creating such a cosmic black hole - it would require a totally insane amount of energy.
Micro black holes are very different from the cosmic black holes. Their mass is very small, and they also don't light escape their event horizon. How they manage to do this if their mass is very small? The answer is very simple. A black hole must satisfy the following equation (more precisely it should be less than and not equality) :
R - radious of the black hole. M - mass of the black hole. G - gravitational constant. c - speed of light.
Any object that satisfies this equation is a black hole. G and c are constants, M is the mass of the micro black hole created by LHC and is therefore also unchangeable. So the only way to create a block hole is by making the radios smaller. The micro black holes are nothing more than a very, very well compressed matter.
LHC is capable of very high energies but they are very small when compared to mass energy.. The energy needed to produce even 1 kg of matter is much more that what is LHC capable of.
Even if a micro black hole would be produce this way it would have no impact on the world around. More precisely, the effect of such a block hole on the objects around it would be exactly the same effect its mass was causing before it was compressed. Noticeable difference would be visible only a very tiny scales - radius of an atom for example. Creation of such a black hole, if it is possible to to create a all, would in no way harm the world - unless it will start growing.
It is very easy to prove that this will not happen, but it is more difficult to understand. The reason is the same as with the "strange matter" .
Strange matter : First of all it is a totally theoretical object. It was never seen, not even in a lab. This is not enough to say that it doesn't exist, but it is enough to say that LHC will not produce any. This is so because LHC energy is much lower than Cosmic rays energy. If it is possible for LHC to destroy the earth by producing micro black holes or strange matter, so it is for these rays. Since we are still not destroyed, there is no reason to worry.