Post a Comment On: Backreaction

Okay, that is my 3rd try to set up a blog. Be patient. My world is a fuzzy sphere and my English reliable only at the 95% confirmation level.

So, what's new today. I got an email from the German 'Federal Office for Information Security', Department "New Technologies". They are concerned (again!) that black holes at LHC are going to eat up the earth. Apparently that was triggered by this paper

http://xxx.lanl.gov/abs/gr-qc/0503053

Quantum character of black holes
Authors: Adam D. Helfer


Black holes are extreme manifestations of general relativity, so one might hope that exotic quantum effects would be amplified in their vicinities, perhaps providing clues to quantum gravity. The commonly accepted treatment of quantum corrections to the physics around the holes, however, has provided only limited encouragement of this hope. The predicted corrections have been minor (for macroscopic holes): weak fluxes of low-energy thermal radiation which hardly disturb the classical structures of the holes. Here, I argue that this accepted treatment must be substantially revised. I show that when interactions among fields are taken into account (they were largely neglected in the earlier work) the picture that is drawn is very different. Not only low-energy radiation but also ultra-energetic quanta are produced in the gravitationally collapsing region. The energies of these quanta grow exponentially quickly, so that by the time the hole can be said to have formed, they have passed the Planck scale, at which quantum gravity must become dominant. The vicinities of black holes are windows on quantum gravity.

I don't see how that makes black holes more dangerous than before. I admit, we don't really know what to do at the Planck scale. But for these things to become dangerous it would take significantly lowered temperatures (in comparison to the semi-classical result) for several orders of magnitude above the Planck scale.

Plus, I don't see how the temperature should be lowerd. It seems to me, Helfer's paper points out that we can't trust the calculation, but it doesn't say the emission rate would be such extremely lowered.

So I wrote the guy not to worry.