10 September 2008

Black holes and the end of the world

The media is full of horror stories of black holes that will swallow up the Earth when researchers turn on the world’s largest particle accelerator, the LHC at CERN near Geneva in Switzerland, on Wednesday, the 10th of September.

People become so fearful of the prophecies of doom that they call the researchers at the Niels Bohr Institute, who are involved with the experiments at CERN. Is it correct, that you want to create black holes and that they are really all consuming and will they bring about the end of the world? Many are really worried.

“The black holes that will potentially be created in the accelerator at CERN will be so microscopically small and they will exist for such an extremely short time, that they disappear almost before they are created. They simply disintegrate”, explains Jørgen Beck Hansen, who is a particle physicist at the Niels Bohr Institute and works with the experiment at CERN.

But many think that even though they are small, they could still be dangerous.

“No, they cannot be dangerous”, he says and explains, that in the 27 km long subterranean tunnel one will send particles around in the opposite direction from each other and accelerate them until they reach almost the speed of light, whereupon they are brought to collide with each other. The collision consists of two hydrogen-nuclei (protons). A proton is made up of even smaller particles, called quarks, and that is the why two particles can collide and potentially create a microscopic black hole.

But in order for that to even be possible the current standard theory would have to be dramatically altered. And if physicists actually succeeded in creating microscopic black holes they would be a billionth of the size of an atom and would exist for less than a billionth of a billionth of millionth of a second. They weigh almost nothing and do not have the time to swallow up anything at all.

Not cosmic vacuum cleaners
In order for a black hole to swallow up anything it needs to have an incredibly high density and in order to find that we need to look out in the universe. Black holes are created, for example, when large stars die in an explosion, where some of the matter is flung out into space, while the core itself collapses and creates a dense mass. The earth would, for example, shrink to a sphere of a few cm in diameter if it became a dense black hole.

A black hole has such a high density that the attractive force at a distance from the object is so strong that nothing can escape – not even light, which is why it is called a black hole. The nightmare scenario where black holes swallow everything originates from science fiction films where spaceships are sucked into the hole and disappear.

“Black holes are not cosmic vacuum cleaners. It is only when one comes close to the black hole that things are drawn into it. Otherwise an object could orbit neatly around a black hole just as the earth revolves around the sun because of its gravitational pull – or fly past”, explains astrophysicist Johan Fynbo, of the Dark Cosmology Centre at the Niels Bohr Institute.

Has always occured
But what if the theories are wrong? Could it then happen?

“No, absolutely not”, answers Jørgen Beck Hansen and explains that for billions of years the earth has been constantly bombarded by protons from the universe with much greater energy than that from LHC.  If black holes can be created at LHC, than they would already have been created in the much more numerous collisions of particles in the earth’s atmosphere – and “the earth has not succumbed after 4½ billion years in existence”, explains Jørgen Beck Hansen. “But we would like to study those types of collisions and therefore we need to create them ourselves”, he explains and looks forward to, that after 14 years of dedicated preparations, they can commence the research that can unravel many of the mysteries of nature and the universe.

Read about black holes and safety at CERN’s homepage: