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CX2SA > SCIENC 09.12.05 02:41l 72 Lines 3721 Bytes #999 (0) @ WW
BID : 4304_CX2SA
Read: GUEST OE7FMI
Subj: Astrophysicists weigh up risks
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Sent: 051209/0032Z @:CX2SA.LAV.URY.SA #:4304 [Minas] FBB7.00e $:4304_CX2SA
From: CX2SA@CX2SA.LAV.URY.SA
To : SCIENC@WW
Astrophysicists weigh up risks of cosmic wipeout
================================================
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.
Cosmic sterilisation
--------------------
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."
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