The LHC demystified or how to dispel misconceptions about the accelerator

As the start-up of the LHC approaches, some people are worried about the possible dangers posed by such a powerful machine. Here are a few key points to reassure them...

Drawing done by Rafel Carreras published in his book «  quand l’énergie devient matière... » This book explains particle physics and the notions of scale and energy in a simple and entertaining way. It is available in French at the CERN reception (only 5 CHF).

Does your neighbour think that the LHC’s collisions will transform the pays de Gex into a huge Emmental cheese? Do you get strange e-mails warning you that you’re going to be sucked into black holes in the accelerator? Of course you know that it’s all just pure fantasy, but do you know how to reply? You can start by reading the following explanations:

You are not going to be destroyed by a Big Bang...

The LHC’s beams do indeed contain a lot of energy, equivalent to a TGV travelling at 150 km per hour. But each beam contains 100 billion particles and only a few of them will collide at the beam crossing points. So only a tiny part of this energy will be released in the collisions. An energy of 1 TeV is often compared to that of a mosquito in flight. Thus the energy of two protons colliding in the LHC corresponds to that of a dozen mosquitoes. So in what way is this accelerator more extraordinary than a huge mosquito farm? The extraordinary thing is that it concentrates this energy into a minute space, smaller than an atom and in fact 10’000 billion times smaller than a mosquito. This is how in this infinitely small space the accelerator is able to recreate energy densities close to those that existed just after the Big Bang.

... or sucked up by a black hole...

In theory, the LHC can produce black holes, but only microscopic ones! Their energy would be the same as that of the collisions and would therefore be equivalent to that of several mosquitoes. These mini-black holes will exist only for a fleeting moment in time since, unlike their giant cousins in space, they will be unable to generate sufficient gravitational force to attract matter. In fact, since its creation some 4.5 billion years ago, the Earth has been bombarded from space by cosmic rays (particles) whose energies are much higher than those produced in the LHC. The Earth has apparently not been damaged by all these mini-black holes which should have occurred naturally.

... and you certainly won’t be contaminated

It is true that the LHC will produce a bit of radioactivity, but it will be confined to the core of the experiments and to the beam-stops and will not be detectable at the surface 100 metres above. In any case, the quantity of radioactivity generated at CERN cannot be compared with that produced by a nuclear power station. As the mosquito comparison demonstrates, the accelerators produce a small amount of energy, but it is concentrated into such a minute space that it is really huge on the subatomic scale. In contrast, electrical power stations must produce a great deal of energy to supply electricity to tens of thousands of homes. There is thus no comparison in the amount and quality of radiation produced. Some of the radioactive elements emerging from the core of a nuclear power station continue to emit radiation for several thousand years, and in some cases for several hundreds of thousands of years. Most of the radionuclides produced in accelerators have lifetimes of less than a few dozen minutes. And the longer-lived radionuclides belong to the "very low activity" category with a half-life of less than a few years. Nevertheless, even though the radioactivity generated at CERN is low, it is still monitored extremely closely, not only by the Laboratory itself but also by the competent monitoring authorities in Switzerland and France.

If these questions and answers do not allay your family’s, friends’, neighbours’ and e-mail correspondents’ concerns, CERN’s Communications Group advises you:

- to consult the following web pages:

- to consult the studies by a group of physicists on the safety of high-energy collisions in Europe and in the United States. It is also worth noting that these analyses have been peer-reviewed by independent experts. The reports can be downloaded from:

And if all these explanations are really not enough, the group of physicists can be contacted at the following e-mail address: