NOTE: This article is for normal people, not scientists. The asterisks (stars) point to more scientific footnotes if you're interested.

You may have heard on TV (September 2008) about a large science experiment happening deep underground in a large tunnel straddling the French-Swiss border. You've probably been told that the purpose of the experiment is to re-create the conditions just after the Big Bang (the moment when the Universe is thought to have come into existence), and you might have heard about the possibility of tiny black holes (micro black holes) and other dangerous phenomena being created by the machine the scientists have built.

This machine is called the Large Hadron Collider or LHC, and in this article I would like to explain very clearly and in the simplest possible terms, one simple fact:

The LHC poses absolutely no risk to the existence of Geneva, planet Earth, humanity or the Universe.

In these terms, the LHC is completely harmless. In fact, two standard operational risks - the escape of liquid helium used to cool the machine, and the tiny beams of particles made in the experiment becoming out of control - are of much greater concern. Both of these risks are already accounted for and the worst possible outcome is that the machine itself would be damaged. Indeed, 1 tonne of liquid helium already escaped during a test in the first two weeks of operation (19th September 2008)¹, with no notable consequences other than causing a fire in the tunnel and a temporary delay while the damage is repaired.

What is the LHC?

To understand why the LHC is harmless, we have to understand what it does. Large Hadron Collider is a very posh way of saying that we take two beams of very tiny particles (called protons^*), point them towards each other and smash them together in a head-on collision. The point of this is to break the protons apart and find out what's inside, so we can see what they're made of^**. This will give us a much greater insight into how the Universe works.

It's all about energy

The LHC is not the first experiment of its kind. The LHC is built in a tunnel previously occupied by a similar machine called LEP II (the Large Electron Positron collider), which was in operation between 1989 and 2000². SLAC - the Stanford Linear Accelerator Center³ - houses a number of similar experiments and has been operational in one form or another since 1966. Other similar machines include the RHIC - Relativistic Heavy Ion Collider - in New York, and the Tevatron in Illinois. RHIC and Tevatron are both operational at the time of writing; RHIC is scheduled for closure in 2009 and Tevatron in 2010, which means the LHC will be the only high-powered such experiment in operation.

The reason we keep building new and bigger machines is that, as we delve into ever smaller particles, the energy you need to break them apart increases. Think how easy it is to burst a balloon open with a pin or by standing on it. Now think how hard it is to break open a walnut. To be able to look inside, we need to work harder and use more energy.

The concerns about the LHC are raised by two kinds of sceptics. One group opposes scientific research in general, beit because it might tell them something they don't want to hear, or because it's not humanity's place to meddle with God's creation. The other group is worried about the amount of energy the LHC smashes the particles together with.

The main accelerator at SLAC can accelerate particles up to 50 GeV (you don't need to worry about the unit of measurement, just the number). LEP II can accelerate them up to 100 GeV (twice as much). RHIC also operates at about 100 GeV and the Tevatron - the most powerful version of this experiment prior to the LHC - operates at 1,000 GeV. The LHC can accelerate protons to 7 TeV, or 7,000 GeV - 7 times more powerful than any previous accelerator.

In each case, safety objections were raised during the design and construction of each accelerator. In each case, the sceptics' fears were shown to be unfounded.

For those of you wondering why the LHC was built underground, it was for cost and logistical purposes, not due to safety concerns - a plot of land large enough for a 27km round tunnel isn't cheap, and the existing tunnel was already excavated prior to building LEP II there. The other currently-running accelerators are above ground.

Cosmic rays

Why aren't we worried about unleashing this amount of energy? In a nutshell, because it's pitifully small compared to what we are being bombarded with every second of every day. The energy with which particles are accelerated to in the LHC is equivalent to being hit in the face by a mosquito⁴. More pertinently, the Earth and everything else in the sky is being constantly bombarded by cosmic rays with much higher energy than anything being created at the LHC. When a cosmic ray strikes Earth, the effect is almost identical to when we bash two particles together in the LHC, except the cosmic ray is alot more powerful^***. This hasn't caused us any problems, and the Earth has been around for about 4,500,000,000 years, so there is no reason to believe the collisions in the LHC will be dangerous. A cosmic ray between 1 and 1,000 times as powerful as an LHC collision strikes the Earth's atmosphere about 250,000 (a quarter of a million) times per second^****.

Black hole hype

Why are so many people claiming the world will come to an end when the LHC is finally switched on properly? Media hype. It was during a thorough safety evaluation of the LHC that scientists themselves proposed the possibility of the so-called micro-black holes being created. These black holes would be created only in very special circumstances, and unlike normal black holes are completely harmless. Micro-black holes are also completely theoretical and have never been observed in the real world.

It is a little difficult to explain in laymen's terms why micro-black holes aren't dangerous, but you can try to think of it like droplets of water or a magnet. In a normal black hole, any nearby stuff gets sucked into the black hole and becomes part of it, just like drops of water or two magnetic objects stick together if they get close enough. The key here is close enough. A micro-black hole is so tiny that it cannot get close enough even to nearby tiny particles to start sucking them in. Black holes constantly lose the particles inside them much like a balloon slowly loses all the air inside it, and the micro-black holes are made from so few particles in the first place (just the two that have collided in the LHC), that they immediately disappear, and the particles which went into the micro-black hole come right back out again^*****.

Micro-black holes have never been observed. If the LHC can create them, then they have already been created by the much higher energy cosmic ray collisions with Earth. We are still alive, therefore they cannot pose any risk if they do exist.

Strangelets

There are alot of other reasons why some people are afraid of the LHC, but the one that has received most attention in the media is the potential creation of a special kind of matter called strange matter. The process by which this might happen is complex, but the crux of the fear is that strange matter - if it exists - is thought to immediately connect to other, normal matter that the rest of the world is made from, and turn it into strange matter. This would create a chain reaction where eventually everything becomes strange matter, destroying us in the process.

There are three main ways strange matter could be produced, and while I won't go into them here, the three possibilities were studied at length before the RHIC (mentioned earlier) was switched on. Of particular note is that strangelets (the catalyst for producing strange matter) are more likely to be produced in lower energy collisions due to the way they work. Since the LHC is vastly more powerful than the RHIC, the chance of strangelets being produced is proportionally lower. No strangelets have ever been observed at the RHIC.

Once again, if strangelets do exist, cosmic ray collisions with Earth would have already created them, therefore they must be harmless.

By the way, it was all irrelevant on 10th September

The media forgot to report a couple of small details on the day of all the press coverage when the LHC was switched on:

1. The operating energy was 450 GeV, which is 15 times less than the 7,000 GeV it will eventually operate at when fully commissioned, and less than half that of the Tevatron which is already fully operational. They were just testing it at low energy first.

2. They didn't actually collide any particles together. All of the safety concerns relate to what will happen when particles collide. On launch day, only one beam of particles was fired at a time in each direction to make sure that they went round the tunnel properly. No particles were aimed towards each other, and they will not be until at least March or April 2009.

Conclusion

The LHC was in design since 1994 and construction since 2000. It is interesting to note that the coalition of objectors known as LHC Defense⁶ chose to wait until March 2008 before filing a lawsuit against the US Department of Energy requesting an injunction to prevent the LHC from being switched on (the DOE is one of the major sponsors of the LHC).

The LHC will provide a huge increase in our understanding of the world around us. If you are in any doubt as to the usefulness or cost-worthiness of this project, consider that the invention of the world wide web was an indirect result of work on its predecessor, LEP II. The LHC will very likely produce other radical new technologies as well as providing experimental results we have been waiting for for many years. Among useful technologies already to come out of the LHC include the LCG (LHC Computing Grid) which provides a way to connect huge numbers of computers together to work on tasks much more efficiently than current networking technology allows. You might also consider that, for every month the US has spent in Iraq since 2003, we could have built two LHC machines^******.

If you'd like to read more detailed information about the safety of the LHC, please refer to the LHC Safety Assessment Group's independent report⁵.

Footnotes

* protons are part of the hadron particle family; the LHC will also collide lead ions in a separate experiment

** protons are composed of two up quarks, one down quark and some gluons; it is the quarks and gluons we are really trying to break apart, to produce the quark-gluon plasma thought to be present moments after the Big Bang

*** the comparison is not entirely valid because cosmic rays strike the atmosphere at an angle rather than head-on, so the average centre of mass energy is lower. For the purposes of demonstrating the LHC's safety, this inconsistency is inconsequential because some cosmic ray collisions will still have a much higher centre of mass energy than that produced in the LHC.

**** based on a cosmic ray-to-Earth collision energy of 10⁸ GeV or higher equating to a head-on collision energy of 14 TeV in the LHC, taking the maximum observed cosmic ray-to-Earth collision energy as 10¹¹ GeV, the number of collisions with Earth's atmosphere between this energy range as 5x10^-14 per second and the area of Earth's surface as 5x10¹⁸ cm². Figures taken from the LHC Safety Assessment Group report on the safety of LHC collisions⁵.

***** the process by which black holes lose matter is called Hawking radiation, and is the result of the quantum spawning/annihilation effect occurring at the black hole's event horizon (a pair of quantum particles is generated in the event horizon; one escapes, the other goes into the black hole and annihilates with its partner anti-particle, causing the black hole to lose mass and shrink).

****** LHC construction cost approximately $4 billion; expected operating cost over the experiment's lifetime $2 billion.

References

1 - Incident in LHC sector 3-4 - CERN Press Release

2 - The LEP experiments - CERN

3 - Stanford Linear Accelerator Center

4 - The safety of the LHC - CERN

5 - Review of the Safety of LHC Collisions - LHC Safety Assessment Group (PDF format)

6 - LHCDefense.org: The official site for citizens against the Large Hadron Collider