A Quantum Diaries Survivor

Black holes hype does not decay February 3, 2009

While the creation of black holes in the high-energy proton-proton collisions that LHC will hopefully start providing this fall is not granted, and while the scientific establishment is basically unanimous in claiming that those microscopical entities would anyway decay in a time so short that even top quarks look longevous in comparison, the hype about doomsday being unwittingly delivered by the hands of psychotic, megalomaniac CERN scientists continues unhindered.

Here are a few recent links on the matter (thanks to M.M. for pointing them out):

• One blog
• A MSNBC piece
• Another blog

The source of the renewed fire appears to be a paper published on the arxiv a couple of weeks ago. In it, the authors (R. Casadio, S. Fabi, and B. Harms) discuss a very specific model (a warped brane-world scenario), in whose context microscopic black holes might have a chance to survive for a few seconds.

Never mind the fact that the authors say from the very abstract, as if feeling the impending danger of being strumentalized, “we argue against the possibility of catastrophic black hole growth at the LHC“. This is not the way it should be done: you cannot assume a very specific model, and then draw general conclusions, because others opposing your view may always use the same crooked logic and reverse the conclusions. However, I understand that the authors made a genuine effort to try and figure out what could be the phenomenology of microscopic black holes created in the scenario they considered.

The accretion of a black hole may occur via direct collision with matter and via gravitational interactions with it. For microscopic black holes, however, the latter (called Bondi accretion) is basically negligible. The authors compute the evolution of the mass of the BH as a function of time for different values of a critical mass parameter , which depends on the model and is connected to the characteristic thickness of the brane. They explicitly make two examples: in the first, when ,  a 10 TeV black hole, created with 5 TeV/c momentum, is shown to decay with a roughly exponential law, but with lifetime much longer -of the order of a picosecond- than that usually assumed for a micro-BH evaporating through Hawking radiation. In the second case, where , the maximum BH mass is reached at after about one second. Even in this scenario, the capture radius of the object is very small, and the object decays with a lifetime of about 100 seconds. The authors also show that “there is a rather narrow range of parameters […] for which RS black holes produced at the LHC would grow before evaporating“.

In the figure on the right, the 10-base logarithm of the maximum distance traveled by the black hole (expressed in meters) is computed as a function of the 10-base logarithm of the critical mass (expressed in kilograms), for a black hole of 10 TeV mass produced by the LHC with a momentum of 5 TeV/c. As you can see, if the critical mass parameter is large enough, these things would be able to reach you in your bedroom. Scared ? Let’s read their conclusions then.

“[…] Indeed, in order for the black holes created at the LHC to grow at all, the critical mass should be . This value is rather close to the maximum compatible with experimental test of Newton’s law, that is (which we further relaxed to in our analysis). For smaller values of , the black holes cannot accrete fast enough to overcome the decay rate. Furthermore , the larger is taken to be, the longer a black hole takes to reach its maximum value and the less time it remains near its maximum value before exiting the Earth.

We conclude that, for the RS scenario and black holes decribed by the metric [6], the growth of black holes to catastrophic size does not seem possible. Nonetheless, it remains true that the expected decay times are much longer (and possibly >>1 sec) than is typically predicted by other models, as was first shown in [4]”.

Here are some random reactions I collected from the physics arxiv blog -no mention of the author’s names, since they do not deserve it:

• This is starting to get me nervous.
• Isn’t the LHC in Europe? As long as it doesn’t suck up the USA, I’m fine with it.
• It is entirely possible that the obvious steps in scientific discovery may cause intelligent societies to destroy themselves. It would provide a clear resolution to the Fermi paradox.
• I’m pro science and research, but I’m also pro caution when necessary.
• That’s what I asked and CERN never replied. My question was: “Is it possible that some of these black might coalesce and form larger black holes? larger black holes would be more powerful than their predecessors and possibly aquire more mass and grow still larger.”
• The questions is, whether these scientists are competent at all, if they haven’t made such analysis a WELL BEFORE the LHC project ever started.
• I think this is bad. American officials should do something about this because if scientists do end up destroying the earth with a black hole it won’t matter that they were in Europe, America will get the blame. On the other hand, if we act now to be seen dealing as a responsible member of the international community, then, if the worst happens, we have a good chance of pinning it on the Jews.
• The more disturbing fact about all this is the billions and billions being spent to satisfy the curiosity of a select group of scientists and philosophers. Whatever the results will yield little real-world benefit outside some incestuous lecture circuit.
• “If events at the LHC swallow Switzerland, what are we going to do without wrist watches and chocolate?” Don’t worry, we’ll still have Russian watches. they’re much better, faster even.

It goes on, and on, and on. Boy, it is highly entertaining, but unfortunately, I fear this is taking a bad turn for Science. I tend to believe that on this particular issue, no discussion would be better than any discussion -it is like trying to argue with a fanatic about the reality of a statue of the Virgin weeping blood.

… So, why don’t we just shut up on this particular matter ?

Hmm, if I post this, I would be going against my own suggestion. Damned either way.