Earthlings can rest easy. The likelihood of a doomsday scenario in which Earth is destroyed in a freak astrophysical catastrophe is remote - about once in a billion years, according to a new calculation.
The calculation was made by Max Tegmark, an astrophysicist at MIT in the US, and Nick Bostrom at the University of Oxford in the UK. The story behind the work begins in 1999, when the media reported concerns that heavy-ion collisions at Brookhaven Relativistic Heavy Ion Collider could spark the destruction of Earth.
Possible scenarios included the formation of a black hole that would gobble up our planet and the creation of a stable "strangelet" that would then convert all normal matter to strange matter. A subsequent study by physicists in 2000 indicated that such events were a thousand times more likely to be caused by a natural event, such as cosmic-ray collisions, than by humans tinkering with a particle accelerator.
But Tegmark and Bostrom were concerned that this analysis could have given humankind a false sense of security, because of a "selection bias". This arises from the fact that if a planet were destroyed by such a catastrophe, there would be no observers remaining to record it.
As a consequence, just because Earth has avoided destruction so far does not necessarily mean that planetary catastrophes are extremely rare - it may just have been lucky.
So the pair took a different approach. For a range of possible rates of cosmic catastrophe, they used data on planetary formation rates to calculate the distribution of birth dates for intelligent species. Combining this with the age of the Earth, they calculate that at most one habitable planet is wiped out every 1.1 billion years.
“The bottom line of this is I think you don’t have to lose too much sleep,” Tegmark told New Scientist.
Tegmark and Bostrom did not limit their work to the hypothetical apocalypses outlined in 2000. They say the calculation should be valid even for cosmological events that have not yet been considered by humans. But it does not account for self-inflicted disasters, such as nuclear annihilation or extinction via engineered microbes. Those scenarios are still worrying, they say.
As for particle accelerators, the new research puts the chances of Earth being destroyed by a freak event at a high-energy physics experiment at about one in a trillion per year.
Samuel Aronson, associate director for high energy and nuclear physics at Brookhaven National Laboratory in Upton, New York, US, is reassured by the findings: “What I conclude from this, as apparently Tegmark and Bostrom do as well, is that human activities, including accelerator science, contribute a tiny amount to the extremely low probability of doomsday catastrophes from any source in our neighborhood.”
Journal reference: Nature (vol 438, p 754)
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