The Mangano-Giddings report on LHC safety is out! June 20, 2008
Posted by dorigo in news, physics, science.Tags: LHC, micro black holes, strangelets
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This just in: the report on the safety of the LHC is out. I have no time to comment it here, will do it tomorrow after a more thorough reading.
In order of increasing complexity, you can start from the CERN press release, look directly at the LSAG report, or concentrate on the physics in the paper by Mangano and Giddings.
After a spoiler warning, I can say that…
There is no danger, and we can go on with the LHC physics program!
Happy reading!
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A Quantum Diaries Survivor 
Hi Tommaso.
I glanced at Magano’s paper. I am please to see that someone really did take seriously the popular worries. I especially liked the argument of how the earth and the sun, over billions of years, would have stopped stable charged blackholes, of pertinent energies. They simply applied Bethe-Bloch! Very cute indeed. Nice excercise for students
This new report provides reasonable evidence that when a stray cosmic ray particle collides with Earth or a Neutron star, dangerous black holes are not produced.
Unfortunately for those of us who do research the details, the report does not directly address the safety of colliding thousands of tightly packed anti-matter particles head on against thousands of tightly packed matter particles at 99.9999991% of the speed of light with powerful magnets and exactly opposing momentums to focus the energy. Planned conditions at the LHC that might create dangerous black holes.
This report simply asks us to make one hell of an assumption, that a single cosmic ray particle impact with Earth or Neutron stars will produce the same results as colliding thousands of anti-matter particles head on against thousands of matter particles with powerful magnets and exactly opposing momentums to focus the energy. We are asked to accept that these conditions must create the same results, without a single scientific explaination to support what appears to me to be a rather far fetched assumption “hence neither will the LHC“.
LHCFacts.org
Each proton bunch includes 10^11 protons, but its size is several mm across, and several cm in length. The average distance between protons is astronomical, even by “chemistry” standards. 10^11 protons is about 10^-13 grams, distributed over something of the order of a cubic centimeter. Is 10^-13 gr/cm^3 what you call tightly packed matter?
Having looked through the reports, I see good things and bad things. The good thing is that the arguments against any danger from black holes are really tight. They are so tight that I am reluctantly willing to accept the absence of standard risk-analysis numbers from the report, ie clearly the expected number of deaths is negligible. The point is that the very physics that is used to argue in favor of danger can be turned around against it. If you don’t believe in Hawking evaporation, then what makes you think that black holes will be produced anyway? That is what I like to see.
The bad thing is the part of the Ellis et al report which deals with strangelets. There is a lot of hand-waving, and much of it amounts to “RHIC didn’t destroy the world, so why worry?”
Let me be clear again: I agree that the risk is tiny. But as a scientist, I don’t like words like “tiny”.
My lack of trust in hand-wavy arguments is based on reading the famous paper
http://arxiv.org/abs/hep-ph/9910333
I urge everyone to look at that and ask themselves how they feel about their bounds for a ten year run of the RHIC experiment of (Cases I-III): pcatastrophe < 2 × 10−11, pcatastrophe < 2 × 10−6,
pcatastrophe < 2 ×10−5. Commenting on these [to my mind shockingly large] numbers, they say: “We do not attempt to decide what is
an acceptable upper limit on [pcatastrophe], nor do we attempt a ‘risk analysis’, weighing the probability of an adverse
event against the severity of its consequences.”
Great, guys. You wash your hands and we are supposed to feel reassured? If these people didn’t take their job seriously, why should we trust Ellis et al?
By the way, one of the authors of the RHIC report subsequently wrote a paper with an interesting title:
http://arxiv.org/abs/physics/0511067
Let’s hope that the title does not come true in a more unpleasant way……..
All CERN has to do is to get together with some world-class actuaries specializing in risk analysis, give us the numbers, and engage in a frank public discussion as to what probabilities are acceptable. I’m sure it can be done and I’m sure that the numbers will be reassuring. But it hasn’t been done yet, and these reports are not a substitute.
The idea that black holes may be produced at LHC is based on large extra dimensional scenarios which are extremely unlikely. The main motivation for these scenarios is an alternative way to solve hierarchy problem, for which there is better solution, supersymmetry. The tevatron has been producing proton/antiproton collision now for several years at a very high energy. The LHC will only do some, but at a slightly higher energy.
Tom,
you raise a reasonable question, and I appreciate your point of view. I also usually either grin or frown when adjectives are used rather than figures. However, the fact that RHIC did not produce anything harmful is indeed a useful information when one wants to determine the threat at LHC. I hope the numbers you quote have decreased since RHIC started running.
Evil ST, I also like that argument. In fact, 2 TeV and 14 TeV are qualitatively the same thing. We are orders of magnitude below the planck scale, and we worry about going up seven-fold….
Cheers,
T.
This report is a good effort, and may well settle the issue. But, the Planck scale, the Planck scale? And who says that’s the scale that matters? Everybody is using Standard Model thinking to analyse quantum gravitational questions. A lot of assumptions are being made, probably very reasonable assumptions to be sure, but they need to be acknowledged as such, because from a legal point of view it isn’t at all clear to me that the physicists have a winning case yet.
Hi Kea,
that is true, assumptions are made here and there. Perhaps I see this as less troubling than you do, because I am accustomed, as an experimentalist, to neglect second-order effects, third digits in error bars, and stuff alike, while a theorist is always aiming at the perfect truth… In this case it does matter, but I think the paper by M and G is more or less as good as it gets…
Cheers,
T.
Many assumptions that might be for naught if… they can’t even find the Higgs. Nobody ever listens to me, but you might have a lot more than black holes to worry about when you put a tiny little needle against a highly inflated balloon:
http://www.lns.cornell.edu/spr/2006-02/msg0073320.html
I hate even bringing it up, because now I’m a fear-monger, but nobody pays any attention to them anyway, so I say… LET ER RIP, BABY!!!
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