Monday, September 10, 2007

Getting naked at LHC, and black hole bombs?

I could be wrong, but I am pretty sure I have never seen CERN, or anyone else, mention the possibility of a naked singularity being created at the LHC rather than (or as well as) mini black holes. Yet it would appear that some credible physicist types think it is still an open question.

Here's an extract from the relevant paper, which is from 2002:
There is thus no compelling reason to discard the possibility that the collision of charged particles produces a naked singularity, an event which would probably be indistinguishable from ordinary particle production, with the naked singularity (possibly) behaving as an intermediate, highly unstable state. The phenomenology of naked singularities is probably rather different from that of black holes, as they are generally expected to explode in a very sudden event instead of evaporating via the Hawking process (at least in an early stage; see, e.g., [20] and Refs. therein).

We should however add that the present literature does not reliably cover the case of such tiny naked singularities and their actual phenomenology is an open question. A naked singularity is basically a failure in the causality structure of space-time mathematically admitted by the field equations of general relativity. Most studies have thus focused on their realization as the (classical) end-point of the gravitational collapse of compact objects (such as dust clouds) and on their stability by employing quantum field theory on the resulting background. However, one might need more than semiclassical tools to investigate both the formation by collison of particles
and the subsequent time evolution [20]. In particular, to our knowledge, no estimate of the life-time of a naked singularity of the sort of interest here is yet available.
I thought that naked singularities had been ruled out as a general concept a long time ago. (They are, as I understand it, the heart of the black hole without the cloaking event horizon.) It would seem from the above that no one has a clear idea how they would behave, or how long they would last. It seems to me something that the safety review for the LHC should address.

Another paper I recently found while trawling the 'net also raises issues I would like to see better explained. This is from someone at Princeton in 2002, and has the cheery title : "Explosive Black hole fission and fusion in large extra dimensions".

The paper seems to be mainly about "explosions" that could be caused by the evaporation process of micro black holes, including those that could be created at the LHC. What remains very unclear to the lay reader is whether the amount of energy involved in this is nothing to worry about, or not. But the paper does end with this curious section:
One cannot avoid considering bomb construction using either fission or fusion ignoring the problems of creating and handling small black holes. A black hole could be prepared close to its critical size ready to fuse and then activated by adding matter and reaching “critical mass”. Timing the fission process is more difficult, since the time for decay is determined by the Hawking radiation which cannot be hurried artificially, but perhaps it is possible to balance the Hawking radiation with incoming radiation until activation. However, these bombs have a big disadvantage, since if one is in possession of small black holes, one could collide them with very similar explosions occurring both in emitted energy and time scale (being a classical process), and since igniting the phase transition seems to be the more complicated process it would probably be disfavoured, and luckily not used for destructive ends.
Err, I wish physicists would be clear when they are using terms like "bomb" and "explosion" in papers which are discussing micro black holes whether they are presenting stuff which indicates possible danger.

This mention of a black hole bomb (and by the way there is another type I haven't mentioned yet) is completely unclear as to whether it is talking science fiction stuff centuries away, or something plausible anytime you can start creating mini black holes at an accelerator.

Some clarification is deserved, as with naked singularities.

(Oh, and the fact that micro black holes may be being created in the atmosphere 100 times a year is relevant to this too, I know. But I still worry about the "stationary" black hole or naked singularity as an issue at the LHC, as naturally occurring ones would normally have high velocity. Also, I am sure I have mentioned a paper recently which suggested that micro black holes may be harder to create than we think, even with large extra dimensions. Perhaps they are made by fluke in the atmosphere only very occasionally, causing events like Tungaska or some unaccounted for atomic blast signals detected by satellite? All possibilities should be addressed, I reckon.)

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