Hi, In the safety case for the new Large Hadron Collider (LHC), the possibility of creating artificial black holes is considered. The main argument for the case that there is nothing to worry about, is that cosmic rays collide regularly with atoms in the upper atmosphere with much higher collision energies than can be produced in the LHC... and yet the Earth is still here... That seams a reasonable argument. We can also note that generally speaking stars do not disappear randomly on a regular basis with no apparent cause. However, it is reasonable to ask why the Earth is still here if black holes are occasionally formed in the upper atmosphere. Some LHC critics argue that any possible micro black holes formed in the upper atmosphere have high velocities and would pass through the Earth with little fuss because they are moving too fast to significantly gravitationally interact with the Earth. There concern is that the collisions in the LHC are due to two particle beams moving in opposite directions would have a net momentum of zero and any micro black hole formed would be more dangerous than a natural cosmic black hole because it not moving fast and has more time to interact gravitationally with its surroundings. Of course that counter argument is based on the assumption that natural cosmic black holes are basically harmless because they pass rapidly through the Earth with greater than the required escape velocity. I do not find that a convincing argument. In the history of the Earth at least one natural micro black hole would in all probability have had a succession of chance collisions with particles in the air and in the body of the Earth itself, sufficient to slow the black hole to below the escape velocity. The high velocity of any natural black holes does not seem sufficient enough argument to explain the observed survival of the Earth. The other argument in the defence of the LHC safety case is Hawking radiation. The half life of a black hole is inversely related to its mass and for a micro black hole the lifetime is very brief before its evaporates in a burst of radiation. Critics counter that Hawking's radiation is only theoretical and has never actually been observed so in their view the safety case is based on something that not been proved empirically. I would add that even with Hawking radiation a rapid series of chance collisions after the formation of a natural black hole would allow it gain mass faster than it loses it through radiation...and yet the Earth is still here... I would like to add a third argument for consideration here. Imagine a micro black hole has managed to survive evaporating away at birth and finds itself at the centre of the Earth. The interior Schwarzschild solution tells us that the gravitational gamma factor at any location with a a massive body is determined by the enclosed mass AND the mass outside the enclosed volume. A quick calculation shows that when the mass of the Earth+micro black hole is taken into account there is no longer an event horizon anywhere inside the earth and the micro black hole is in fact destroyed (in that it no longer has the properties of being a black hole) by the mass of the Earth rather than the other way round. It turns out that micro black hole holes are quite delicate creatures that have to be carefully nurtured to survive. At the baby stage they have to be fed frequently at the correct intervals to avoid evaporating between meals until they get to a juvenile stage where their mass is self sustaining because they gain energy from the CMB faster than they evaporate. Even when they survive to that stage, care has to be taken not to overfeed the black hole, as it seems too big a meal (where the mass of the meal greatly exceeds the mass of the black hole) at any one sitting can cause them to choke and die.