Any black holes created at a new particle accelerator near Geneva will not make Swiss cheese of the nearby countryside. Nor will they gobble up Earth.
That’s the consensus of two new reports, including a safety review released June 20 by the European Organization for Nuclear Research, or CERN, the group that oversees the Large Hadron Collider (http://arxiv.org/abs/0806.3414).
Scheduled to start this September, the collider will be the most powerful particle accelerator in the world. Protons in the accelerator will reach energies of 7 trillion electron volts and smash into each other at nearly the speed of light, briefly re-creating the extreme densities and energies existing a tiny fraction of a second after the Big Bang.
Some people, including a group based in Hawaii that has filed a lawsuit against CERN, worry that those collisions could somehow generate stable black holes that might swallow the planet.
In fact, it is possible that the LHC, according to one theory, could be a veritable factory of mini-black holes — no larger than a thousandth of the diameter of a proton.
That theory proposes that gravity is weak, compared to the other forces in nature, because some of it leaks out into other, hidden dimensions folded up into sizes as small as 10-17 centimeters, a tiny fraction of the diameter of a hydrogen atom.
At the high energies and small scales probed by the LHC, gravity would become much stronger than it is in ordinary three-dimensional space. Gravity could then cram enough matter together to form microscopic black holes as often as once a second.
However, such black holes, according to research first reported by Stephen Hawking in the 1970s, ought to rapidly radiate away their energy and evaporate in an instant, before doing any harm. But even if Hawking is wrong, and tiny black holes linger, they still would not pose a danger, according to the new studies.
Study member John Ellis of CERN noted that the CERN safety report was independently reviewed by a group of 20 scientists outside CERN, including Nobel laureate Gerard ‘t Hooft, an expert on black hole theory.
The report also relies on a separate study, by Steve Giddings of the University of California, Santa Barbara and Michelangelo Mangano of CERN, set to appear in an upcoming Physical Review D.
Both studies reaffirm the findings of a 2003 CERN report that the high-energy collisions generated at the LHC would pose no danger to Earth.
The studies note that cosmic rays — charged particles from outer space that have energies far greater than those generated at the LHC — have pummeled Earth for billions of years. These collisions could have generated as many black holes as a million LHC experiments, yet the planet still exists. Cosmic rays also bombard dense stars — white dwarfs and neutron stars — yet those bodies endure despite the fact that any encounter with a black hole would consume these objects much more rapidly than they would Earth, notes Ellis.
The possibility of even creating tiny black holes at the LHC is “quite a long shot,” notes Giddings. But he’s hoping that long shot comes through.
“Not only would we learn things about gravity and the fabric of space-time, but we would apparently have direct evidence for extra dimensions of space,” Giddings says. It might also serve to unify gravity with the other forces in nature.