Back in 2000, when the Brookhaven Relativistic Heavy Ion Collider came on line, there was speculation that the high-energy subsatomic experiments might result in the catastropic destruction of the Earth. Implausibly, a subatomic-sized black hole or gravitational singularity, created in the accelerator, would accrete ordinary matter, eventually (in a flash) gobbling up the Earth. Or, alternately, a stable "strangelet" might accrete ordinary matter and convert it into strange matter. Poof!
The upshot of either scenario would be instantaneous destruction of the planet.
The Large Hadron Collider at CERN near Geneva comes on line next year, and scaremongers now raise the same concerns. It's rather like the anxieties of physicists before the first nuclear explosion in 1945: Would the blast at Alamogordo ignite the atmosphere by fusion and destroy the Earth? When the bomb exploded, the confidence of at least one physicist was briefly tested. Emilio Segre, an eyewitness and nuclear scientist, wrote: "We saw the whole sky flash with unbelievable brightness in spite of the very dark glasses we wore...I believe that for a moment I thought the explosion might set fire to the atmosphere and thus finish the earth, even though I knew that this was not possible." Why impossible? Physicists had done the calculations and decided the chances of catastrophe were infinitesimal.
A recent accessment published in Nature suggests that the risk from the present generation of accelerating machines is reassuringly less than 0.000000000001 per year. But not to worry. If the physicists suck the world into oblivion, it will happen so fast that we'll won't have time to wring our hands and rue.
Maybe those folks who are searching for signs of intelligent life in the universe are looking for the wrong things. Instead of tuning their instruments to the extraterrestrial equivalent of Beethoven's Ninth, they should look for brief, bright flashes of annihilation.