http://physicsworld.com/cws/article/...ected-energies
Micro black holes could form at lower-than-expected energies
Mar 15, 2013 16 comments
New simulations of head-on collisions of particles travelling at nearly the speed of light show that black-hole formation can occur at lower collision energies than expected, according to a team of researchers in the US. The researchers attribute this to a "gravitational focusing effect" whereby the two colliding particles act like gravitational lenses, focusing the energy of the collision into two distinct light-trapping regions that eventually collapse into a single black hole. Although the work shows that black holes can form at lower collision energies than expected, the team says that the result has no impact on real particle collisions taking place at the Large Hadron Collider (LHC) at CERN.
From 2008 onwards, when the LHC was first scheduled to be switched on, there were rumours about what the experiment might create – extra dimensions, sparticles and strangelets, vacuum bubbles and, of course, planet-destroying black holes. Although the experiment ran seamlessly from November 2009 for more than two years and scientists found no evidence whatsoever for the formation of micro black holes, the fascination with black-hole formation and evaporation continues – among researchers and the media.
Planck scales and beyond
Frans Pretorius and William East of Princeton University in the US want to better understand the dynamics of particle collisions at the super-Planck scale.
Planck units are a system of units comprised of the simplest algebraic combinations of the fundamental constants of nature – the speed of light c, Newton's constant G, Planck's constant h and so on. For example, a combination of the constants to form a unit of Planck energy (Ep) is about 2 × 109 J. Pretorius explains that a super-Planck-scale collision is a collision between two fundamental particles where the total energy (rest energy (Er) plus the kinetic energy) exceeds Ep. At the Planck scale, quantum-gravity effects are expected to start playing a role in the interaction. However, at energies greater than Ep (and no-one knows exactly how much greater), classical gravity dominates the interaction.
So the researchers wanted a completely classical calculation, and this, explains Pretorius, is the "crucial ingredient in the argument that super-Planck-scale collisions form black holes, regardless of any non-gravitational interactions between the particles". He goes on to explain that this is important, as
currently we do not know exactly what quantum-gravity interactions occur at the Planck scale. According to Pretorius, the new results suggest that for energies sufficiently above the Planck scale it does not matter – a black hole will form around the interaction, hiding all quantum effects, at least temporarily.