Probability of Spontaneous Annihilation of Earth

From this week's Nature (Tegmark and Bostrom, Nature 438, 754):

Fears that heavy-ion collisions at the Brookhaven Relativistic Heavy Ion Collider might initiate a catastrophic destruction of Earth have focused on three possible scenarios: a transition to a lower vacuum state that propagates outwards from its source at the speed of light; formation of a black hole or gravitational singularity that accretes ordinary matter; or creation of a stable 'strangelet' that accretes ordinary matter and converts it to strange matter. A careful study concluded that these hypothetical scenarios are overwhelmingly more likely to be triggered by natural high-energy astrophysical events, such as cosmic-ray collisions, than by the Brookhaven collider.

Given that life on Earth has survived for nearly 4 billion years (4 Gyr), it might be assumed that natural catastrophic events are extremely rare. Unfortunately, this argument is flawed because it fails to take into account an observation-selection effect, whereby observers are precluded from noting anything other than that their own species has survived up to the point when the observation is made. If it takes at least 4.6 Gyr for intelligent observers to arise, then the mere observation that Earth has survived for this duration cannot even give us grounds for rejecting with 99% confidence the hypothesis that the average cosmic neighbourhood is typically sterilized, say, every 1,000 years. The observation-selection effect guarantees that we would find ourselves in a lucky situation, no matter how frequent the sterilization events.


You'll be relieved to hear that the authors believe the annihilation rate to be no more frequent than every billion years-- based on natural phenomena. They make no promises about the frequency of intelligent species developing and annihilating their planets.