By Paul Rincon

Science reporter, BBC News

Atlas is the biggest experiment housed at the LHC Our planet is not at risk from the world's most powerful particle physics experiment, a report has concluded. The document addresses fears that the Large Hadron Collider is so energetic, it could have unforeseen consequences. Critics are worried that mini-black holes made at the soon-to-open facility on the French-Swiss border might threaten the Earth's very existence. But the report, issued the European Organization for Nuclear Research, says there is "no conceivable danger". The organization - known better by its French acronym, Cern - will operate the collider underground in a 27km-long tunnel near Geneva. This Large Hadron Collider (LHC) is a powerful and complicated machine, which will smash together protons at super-fast speeds in a bid to unlock the secrets of the Universe. Six "detectors" - individual experiments - will count, trace and analyse the particles that emerge from the collisions. Most physicists believe the risk of a cataclysm lies in the realms of science fiction. But there have been fears about the possibility of a mini-black hole - produced in the collider - swelling so that it gobbles up the Earth. Critics have previously raised concerns that the production of weird hypothetical particles called strangelets in the LHC could trigger the mass conversion of nuclei in ordinary atoms into more strange matter - transforming the Earth into a hot, dead lump. New particles The lay language summary of the report, which has been written by Cern's top theorists, states: "Over the past billions of years, nature has already generated on Earth as many collisions as about a million LHC experiments - and the planet still exists." The report added: "There is no basis for any concerns about the consequences of new particles or forms of matter that could possibly be produced by the LHC." If a black hole is produced, it might look like this in LHC data The new document is an update of the analysis carried out in 2003 into the safety of the collider by an independent team of scientists. The authors of the latest report, including theoretical physicist John Ellis, confirmed that black holes could be made by the collider. But they said: "If microscopic black holes were to be singly produced by colliding the quarks and gluons inside protons, they would also be able to decay into the same types of particles that produced them." The report added: "The expected lifetime [of a mini-black hole] would be very short." On the strangelet issue, the report says that these particles are even less likely to be produced at the LHC than in the lower-energy Relativistic Heavy Ion Collider (RHIC) in New York, which has been operating since 2000. A previous battle over particle accelerator safety was fought over the US machine. 'Fundamental question' The scientific consensus appears to be on the side of Cern's theorists. But in 2003, Dr Adrian Kent, a theoretical physicist at the University of Cambridge, wrote a paper in which he argued that scientists had not adequately calculated the risks of a "killer strangelet" catastrophe scenario. He also expressed concern that a fundamental question (how improbable does a cataclysm have to be to warrant proceeding with an experiment?) had never been seriously inspected. The LHC was due to switch on in 26 November 2007. The start-up has been postponed several times, however, and is currently scheduled for later this summer. The first delay was precipitated by an accident in March 2007 during stress testing of one of the LHC's "quadrupole" magnets. A statement carried on the Cern website from the US laboratory that provided the magnet stated that the equipment had experienced a "failure" when supporting structures "broke". It later emerged that the magnet had exploded in the tunnel, close to one of the LHC's most important detectors. No one was in the immediate vicinity of the test, so there were no injuries. The magnet problem was fixed shortly afterwards. In March, a complaint requesting an injunction against the LHC's switch-on was filed before the United States District Court for the District of Hawaii by seven plaintiffs. One of the plaintiffs had previously attempted to bring a similar injunction against the RHIC over safety concerns. Paul.Rincon-INTERNET@bbc.co.uk



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