Strange Explosions

Or When to Take Big Risks

STATISTICIANS have a saying: ``There is a non-zero probability that the planet will explode in the next five minutes'', meaning, of course, that the probability of every conceivable event is greater than zero. You think, no doubt, that perpetual motion machines can never be built; that faster than light travel can never take place. But no true statistician would agree with that. He would agree that both accomplishments are extremely unlikely, but he would wince at the word ``never.'' How do you know, he would say, that the laws of nature are not going suddenly to change?

Normally this kind of remark can be dismissed as an academic joke with no relevance to the real world. But sometimes the probability of a catastrophic event seems to rise from the infinitesimal to the tiny, and people start getting excited about it. An example is an extraordinary new controversy about whether a laboratory experiment can literally destroy the Earth. I'm not talking about the possible release of a dangerous virus, but a change in the character of matter itself that might wreck the entire planet. In the words of the Rome University physicist Francesco Calogero, it could compress the planet to within a diameter of 100 metres but with all its original mass. This could be followed, he suggests, by ``an explosion of astronomical proportions'' that would wipe out all life. I'd be happy to announce that Calogero's warning appeared on April 1, but unfortunately this is not the case. It appears in a lengthy article in the autumn 2000 issue of Interdisciplinary Science Reviews, and it makes scary reading. Calogero is worried about the safety assurances accompanying a project to be carried out at the atom-smashing machine at Cern in Geneva called ALICE, short for ``A Large Ion Collider Experiment.'' The idea of smashing groups of very heavy atoms together at close to the speed of light - and my account of this is somewhat approximate—is to discover and create strange new forms of matter, or ``strangelets'', that might have been present at the Big Bang. Everything on Earth consists of the particles that make up the atoms of ordinary matter. But strange matter might consist of atoms that have been differently formed; and the two sorts might prove to be violently incompatible. In a worse possible case, one strangelet created by ALICE would attract an ordinary atom, join with it, and become a still larger strangelet. This process would continue until all surrounding matter had been rendered ``strange'', including the planet itself and everything on it. If not a colossal explosion, the result might be a black hole into which we would all vanish. Now the chances of anything like this happening are extremely remote, perhaps one in trillions over many years of running ALICE. We'd all be far safer smoking 200 cigarettes a day. And so the interesting question is whether the risk is worth it. On one hand we may acquire deep knowledge that may one day enable us to build starship engines. On the other we may become immediately extinct. Calogero's view (and mine) is that it's worth risking, but he accuses worries about the ``lack of candour'' of the experts weighing the risks. He deplores the experts weighing the risks of a ``lack of candour'' and of wishing to ``reassure the public'', rather than objectively assess the facts. And in one extraordinary case the journal Nature rejected a paper on the subject on the grounds that it would be of no interest to its readers! Perhaps there's another way of looking at it. If ALICE kills us all we won't know it and there'll be no regrets. But if the project gives us the ability to fly to the stars, posterity will be grateful for our heroic decision. Lets's go for it.