Safety at the LHC
The Large Hadron Collider (LHC) can achieve energies that no other particle accelerators have reached before. The energy of its particle collisions has previously only been found in Nature. And it is only by using such a powerful machine that phyicists can probe deeper into the key mysteries of the Universe. Some people have expressed concerns about the safety of whatever may be created in high-energy particle collisions. However there are no reasons for concern.
Modest by Nature's standards
Accelerators recreate the natural phenomena of cosmic rays under controlled laboratory conditions. Cosmic rays are particles produced in outer space in events such as supernovae or the formation of black holes, during which they can be accelerated to energies far exceeding those of the LHC. Cosmic rays travel throughout the Universe, and have been bombarding the Earth's atmosphere continually since its formation 4.5 billion years ago. Despite the impressive power of the LHC in comparison with other accelerators, the energies produced in its collisions are greatly exceeded by those found in some cosmic rays. Since the much higher-energy collisions provided by Nature for billions of years have not harmed the Earth, there is no reason to think that any phenomenon produced by the LHC will do so.
Cosmic rays also collide with the Moon, Jupiter, the Sun and other astronomical bodies. The total number of these collisions is huge compared to what is expected at the LHC. The fact that planets and stars remain intact strengthens our confidence that LHC collisions are safe. The LHC's energy, although powerful for an accelerator, is modest by Nature's standards.
TGVs and mosquitoes
The total energy in each beam of protons in the LHC is equivalent to a 400 tonne train (like the French TGV) travelling at 150 km/h. However, only an infinitesimal part of this energy is released in each particle collision - roughly equivalent to the energy of a dozen flying mosquitoes. In fact, whenever you try to swat a mosquito by clapping your hands together, you create a collision energy much higher than the protons inside the LHC. The LHC's speciality is its impressive ability to concentrate this collision energy into a minuscule area on a subatomic scale. But even this capability is just a pale shadow of what Nature achieves routinely in cosmic-ray collisions.
During part of its operation, the LHC will collide beams of lead nuclei, which have a greater collision energy, equivalent to just over a thousand mosquitoes. However, this will be much more spread out than the energy produced in the proton collisions, and also presents no risk.
Microscopic black holes will not eat you...
Massive black holes are created in the Universe by the collapse of massive stars, which contain enormous amounts of gravitational energy that pulls in surrounding matter. The gravitational pull of a black hole is related to the amount of matter or energy it contains – the less there is, the weaker the pull. Some physicists suggest that microscopic black holes could be produced in the collisions at the LHC. However, these would only be created with the energies of the colliding particles (equivalent to the energies of mosquitoes), so no microscopic black holes produced inside the LHC could generate a strong enough gravitational force to pull in surrounding matter.
If the LHC can produce microscopic black holes, cosmic rays of much higher energies would already have produced many more. Since the Earth is still here, there is no reason to believe that collisions inside the LHC are harmful.
Black holes lose matter through the emission of energy via a process discovered by Stephen Hawking. Any black hole that cannot attract matter, such as those that might be produced at the LHC, will shrink, evaporate and disappear. The smaller the black hole, the faster it vanishes. If microscopic black holes were to be found at the LHC, they would exist only for a fleeting moment. They would be so short-lived that the only way they could be detected would be by detecting the products of their decay.
...nor will strangelets
Strangelets are hypothetical small pieces of matter whose existence has never been proven. They would be made of 'strange quarks' – heavier and unstable relatives of the basic quarks that make up stable matter. Even if strangelets do exist, they would be unstable. Furthermore, their electromagnetic charge would repel normal matter, and instead of combining with stable substances they would simply decay. If strangelets were produced at the LHC, they would not wreak havoc. If they exist, they would already have been created by high-energy cosmic rays, with no harmful consequences.
Reports and reviews
Studies into the safety of high-energy collisions inside particle accelerators have been conducted in both Europe and the United States by physicists who are not themselves involved in experiments at the LHC. Their analyses have been reviewed by the expert scientific community, which agrees with their conclusion that particle collisions in accelerators are safe. CERN has mandated a group of particle physicists, also not involved in the LHC experiments, to monitor the latest speculations about LHC collisions; this group may be contacted at
lsag@cern.ch.
http://public.web.cern.ch/public/en/LHC/Safety-en.html