Worrisome-sounding news in the blogosphere today: two scientists (Matthew Choptuik and Frans Pretorius) report computer simulations proving that black holes actually can form in a collision of two particles. At first glance it sounds like more fodder for those who oppose the Large Hadron Collider in fear of Earth-gobbling black holes.
So - scary, or not very?
I would say not very. We already knew, for all intents and purposes, that particle collisions could make a black hole at high enough energies. It's nice to see it actually happen in a full computer simulation of classical General Relativity, it doesn't add greatly to the debate, especially as the energies simulated were far beyond the LHC.
The LHC debate really hinges on two issues: 1) does "new physics" (such as extra dimensions) permit formation of holes at lower energies, such as found at the LHC; and 2) could those holes grow uncontrollably. Issue (2) is clearly the big one, and the general consensus is that tiny holes evaporate immediately and do not grow, but one can be forgiven for finding this less than fully reassuring.
Personally, I am not worried about rampaging black holes for the following reason. Powerful cosmic rays strike the Earth every second, many with energies far beyond those of the LHC. This has been going on for 4 billion years, so if black holes could form and grow from such collisions then the Earth would have been swallowed long before we ever materialized to worry about it.
I can't help but reflect how much fuss would have been spared had the U.S. gone ahead and built the SSC back in the 90's, before the possibility of black hole formation had even been imagined. Furthermore, physicists would have been spared two more decades of theorizing in a vacuum, with no data; and finally, the SSC was considerably more powerful than the LHC will be.
Ah, what might have been.