Re: I understood that tiny blackholes were very unstable.
well, the big 'uns, by all data to date are formed by a runaway fusion reaction of stellar scale pushing down towards the bottom of a gravity well on a core of neutronium ( itself generated by a runaway fusion reaction of stellar scale pushing... well you get the picture..).
Mind.. in absence of any matter or radiation they still evaporate, it just takes 100's of billions of years.
The little ones... well if the LHC manages to somehow bash things together so hard neutrons actually fuse ( which in and of itself should give off a pretty distinctive signal) and a black hole is created... you run into some interesting problems..
There's the Schwarzschild radius ( for all practical purposes, the event horizon) , for instance, which for a mass of the mount everest would be less than a nanometer, let alone for a couple of neutrons. The lifetime of such a black hole would be femtoseconds, if even that long. Even if one is formed, a black hole that size would not have time to interact with anything.
Mind.. I like worst case scenarios, so let's see..
The LHC does manage to create a black hole, and by sheer coincidence it's smack in the middle of the beam, so it actually gets fed mass and energy by the LHC itself. pretty scary stuff..
Until you realise that all that would happen is that the black hole could "eat" no more than the mass + energy in the beam. As impressive as the energies in the LHC are, that would still never amount to more than a couple of kilos in mass. Giving us a black hole that would be far less than a nanometer across, and doesn't live long enough to interact with anything it isn't fed directly.. Its disintegration at that mass would be a bit tricky though, it'd make a nice Bang!.
But even in that scenario all that would happen is that the beams in the LHC suddenly "disappear" , followed by the random destruction of a lot of expensive equipment ( and perhaps a bit of real estate). The black hole itself would never be able to "swallow the Earth" , it simply doesn't live long enough.