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LHC: Safety analysis

An analysis of the risks associated with large particle colliders, using the Large Hadron Collider at CERN as an example.

Part 1: Overview and introduction

The Large Hadron Collider (LHC) is often described as “the biggest experiment ever,”1 and it lives up to its reputation. The LHC is housed in a 27km-circumference tunnel that crosses the French-Swiss border 4 times. It is expected (at the time of writing) to start operating 'sometime this year,' and when it does, it is expected to:

Unfortunately, this wonderful experiment could very well be delayed due to legal appeals for a restraining order.

Yes, you read that right. On March 21st, 2008,

"[Former nuclear safety officer Walter Wagner] and another critic of the LHC's safety measures, Luis Sancho, filed a lawsuit in Hawaii's U.S. District Court. The suit calls on the U.S. Department of Energy, Fermilab, the National Science Foundation and CERN to ease up on their LHC preparations for several months while the collider's safety was reassessed."2

The short answer to their lawsuit is "HAHAHA NO." However, a large number of people bleating is still a lot of noise, and it would be a terrible shame if the LHC project were put on hold or cancelled because of the monkeys in our minds. So there have been safety reports, such as the LSAG (LHC Safety Assessment Group) report3. Now, I think that should be the end of the issue - a group of highly trained professionals has looked at a lot of difficult maths and complicated data, and have decided the LHC poses no threat - but some people are happy to ignore this, or pretend they know better, or try to split the hairs even finer to find a way the world could still end.4

Arguing with this attitude is impossible, and thankfully these people are very much a minority. However, that's not enough of a reason to do nothing about it. Being, in my own delusions at least, something of a physicist, debator and good person, I have taken it upon myself to add another nail to the "LHC=bad" coffin.
Note: my physics isn't as good as I like to think it is. When I make some glaring error, tell me as soon as possible. The same applies to spelling, grammar and structural failures. More important note: I'm going to use symbols like × instead of *. I find the "keyboard maths" to be like poetry in Russian: it may very well be good, but I can't follow it at all. If your browser doesn't support these... well, if enough people complain, I'll probably change this.

The Opposition

Many claims, from the raving bonkers to the deserving-of-a-looking-at, have been made about the LHC. The most common claim by far is that it could create a black hole or micro black hole5, that would then proceed to swallow the earth. The second most common is that it would produce a "strangelet," a lump of "strange matter" that would convert the earth into more strange matter, Ice-Nine style. Other ideas include bubbles of 'true vacuum' that would destroy everything, as well as a variety of other ideas whose sanity is too low to justify being mentioned here.

Now the normal objection raised to these points is that all astronomical bodies (earth included) are frequently exposed to cosmic rays that have a far, far higher energy then anything some poxy little accelerator could cook up. And this is true: collisions in the LHC will have an energy of up to 14 TeV6, whereas cosmic ray collisions have been measured with energies of 1020 eV7(108TeV).

If you already know what an electronvolt is, skip the next few paragraphs, and please bear with me: there's no point preaching to the choir about this, so I need to make sure everyone reading this knows what's going on (I assume everyone has a working understanding of high school physics). People could click the links, but that can become confusing when each term you look up requires you to look up two or three more at least, as anyone who has tried to learn a piece of science from, say, Wikipedia will know. The problem isn't so bad here, but it's important to minimise people's confusion on issues like this.

"eV" means "electronvolt." It's a measure of energy used in physics for really, really tiny amounts of energy. One electronvolt is the energy needed to move one (unbound) electron through a potential difference of one volt, in a vacuum. It could therefore also be described as the energy gained by an electron when it is so moved. The trick is to imagine that the potential difference (voltage) is a hill, up which the electron climbs. Just as when you climb a hill, you gain gravitational potential energy, so a charged object moving 'up' a potential difference gains electrostatic potential energy.

Now, voltage/potential difference, is a measure of how much energy is given to each unit of charge. One volt = one joule/coulomb. The amount of energy expressed by an eV is therefore equal to one volt (the potential difference the electron is moved through) multiplied by the charge of an electron, 1.60217646 × 10-19.8 This means that an eV is equal to 1.60217646 × 10-19J.

It therefore sounds less than impressive to hear that building a massive, awesome machine nonetheless achieves energies of merely 14 TeV in a collision:
14 TeV = 14 Tera electronvolts
            = 1.60217646 × 10-19 × 1012 × 14
            = 2.243047044 × 10-6J
This is (roughly) 7140000 times less than the energies obtained in some collisions of cosmic rays with particles in the upper atmosphere:
1020 TeV = 1.60217646 × 10-19 × 1020
16.0217646J ÷ 2.243047044 × 10-6J = 7140000

The argument usually goes that if the LHC produces collisions energetic enough to produce black holes, strange matter or other threats to the continued existence of the earth, a cosmic ray collision would have done the same at least once in the last 4.6 billion years or so. The existence of the earth indicates that this has not happened, and hence will not happen in the LHC.

However, the Opposition is persistent, and they're not going to be fobbed off with any so-called scientists' crazy "facts," oh no. They're going to come up with a reason why the LHC can still destroy the world. In this case:

"a single rare high energy cosmic ray may involve a single proton impact with a relatively stationary particle on Earth and send all results safely into space, while collider collisions may involve thousands of protons (or protons to anti-protons) colliding head-on at 99.9999991% of the speed of light in both directions in temperatures lower than space with powerful magnetic fields to help focus all the energy to a single point in space and particles created may be captured by Earth’s gravity."9
Translation: the product of a cosmic ray collision would be travelling very quickly relative to the earth, but a product of a collider collision is relatively motionless. Hence, they claim, a cosmic ray collision product wouldn't stay near the earth, but a particle accelerator collision product would be trapped by the earth's gravity. I'll give some of the above statement a quick going-over in the appendix, but first I want to prove that, even if this were correct, the Large Hadron Collider would still not be a threat to the earth's continued existence.

So then: could the LHC really create a (micro) black hole? If so, is that a threat to the earth?

Forward to part 2 ⇒



1 - http://www.physics.org/featuredetail.asp?newsid=14
2 - http://cosmiclog.msnbc.msn.com/archive/2008/03/27/823924.aspx
3 - http://lsag.web.cern.ch/lsag/LSAG-Report.pdf
4 - http://www.lhcconcerns.com/LHCConcerns/Forums/phpBB3/viewtopic.php?f=18&t=254
5 - http://www.risk-evaluation-forum.org/anon1.htm
6 - http://physicsworld.com/cws/article/print/26015
7 - http://www.unisci.com/stories/20021/0322022.htm
8 - http://www.google.co.uk/search?hl=en&q=charge+on+an+electron&btnG=Google+Search&meta=
9 - http://www.lhcfacts.org/?cat=5

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