Thursday, December 28, 2006

Apocalypse Now

How unlikely is a doomsday catastrophe? de Max Tegmark (MIT) e Nick Bostrom (Oxford)

«Numerous Earth-destroying doomsday scenarios have recently been analyzed, including breakdown of a metastable vacuum state and planetary destruction triggered by a "strangelet'' or microscopic black hole. We point out that many previous bounds on their frequency give a false sense of security: one cannot infer that such events are rare from the the fact that Earth has survived for so long, because observers are by definition in places lucky enough to have avoided destruction. We derive a new upper bound of one per 109 years (99.9% c.l.) on the exogenous terminal catastrophe rate that is free of such selection bias, using planetary age distributions and the relatively late formation time of Earth. (...)

We have shown that life on our planet is highly unlikely to be annihilated by an exogenous catastrophe during the next 109 years. This numerical limit comes from the scenario on on which we have the weakest constraints: vacuum decay, constrained only by the relatively late formation time of Earth. conclusion also translates into a bound on hypothetical anthropogenic disasters caused by high-energy particle accelerators. This holds because the occurrence of exogenous catastrophes, e.g., resulting from cosmic ray collisions, places an upper bound on the frequency of their anthropogenic counterparts. Hence our result closes the logical loophole of selection bias and gives reassurance that the risk of accelerator-triggered doomsday is extremely small, so long as events equivalent to those in our experiments occur more frequently in the natural environment. Specifically, the Brookhaven Report suggests that possible disasters would be triggered at a rate that is at the very least 103 times higher for naturally occurring events than for high-energy particle accelerators. Assuming that this is correct, our 1 Gyr limit therefore translates into a conservative upper bound of 1/103×109 = 10-12 on the annual risk from accelerators, which is reassuringly small.»
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