some people thought the lhc could create a black hole, which would be very dangerous. there are two reasons not to be worried. the first is that the lhc didn't do anything that the cosmic rays that hit the earth every day don't do, and these rays do not create black holes. the second reason is that even if the lhc did make black holes, they would be very tiny. the smaller a black hole is, the shorter its life. very tiny black holes would evaporate before they could hurt people.