THE probability that dangerous Earth-devouring particles will be born at a
new particle accelerator in the US may be tiny, but scientists have played down
the devastating potential costs in their risk assessments, a physicist now
says.
Adrian Kent of Cambridge University accepts that the chances of catastrophe
are minuscule. But he claims physicists are not accounting for the scale of the
potential devastation鈥攖he destruction of the entire planet鈥攊n their
risk analysis. 鈥淪mall catastrophe risks are more costly than we鈥檝e generally
considered,鈥� says Kent.
Last year, sensational newspaper reports suggested that a new particle
accelerator, the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National
Laboratory on Long Island, could put the Earth in peril. The accelerator might
create blobs of matter called strangelets containing 鈥渟trange鈥� quarks, as well
as the usual 鈥渦p鈥� and 鈥渄own鈥� types in ordinary matter. If a strangelet were
stable and negatively charged, it might begin eating the nuclei of ordinary
matter, converting them into strange matter. Eventually this could consume the
entire Earth.
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Physicists reassured the public by pointing out that such a chain of events
is nigh-on impossible (快猫短视频, 28 August 1999, p 24).
The main reason for their confidence is that it鈥檚 very unlikely that strangelets
would be stable or negatively charged.
Astronomical evidence is also reassuring. Heavy ion collisions occur
naturally, for instance when cosmic rays smash into heavy nuclei on the Moon.
Yet the Moon has existed for 5 billion years without being devoured by a
ravenous strangelet.
Arnon Dar, Alvaro De R煤jula and Ulrich Heinz of the CERN particle
physics laboratory near Geneva used the fact that stars are not being changed
into strange matter at a significant rate to calculate the maximum probability
of the Brookhaven collider creating a dangerous strangelet during the
accelerator鈥檚 lifetime. The result was less than 20 chances in a billion, which
the team called 鈥渁 safe and stringent upper bound鈥� (Physics Letters B,
vol 470, p 142). Thus reassured, the Brookhaven lab set RHIC running in
June.
But Kent now argues that this probability is far from acceptable when
compared with risk assessments of other possible hazards, which factor in the
scale of the devastation if things go wrong. He points out that radiological
protection policy in Britain deems it unacceptable for solid nuclear waste to
pose more than a one-in-a-million chance of killing around five people a year on
average. To achieve the same level of risk, global annihilation by a strangelet
would have to have a probability of 1 in 10-15 or less, because it has
the potential to wipe out all 6 billion people on the planet.
John Marburger, director of the Brookhaven lab, does not accept this line of
argument. He says that the risk limit calculated by the CERN researchers was not
a safety assessment in the sense used in nuclear energy safety analysis. 鈥淚n my
opinion, no such risk assessment is possible,鈥� says Marburger. 鈥淲e do not know
how a `dangerous strangelet鈥� would be created, and we do not know the properties
of one if it were.鈥�
De R煤jula agrees. 鈥淲e鈥檝e been standing on our heads to try to convince
people it鈥檚 not true and to come up with limits on it, and this number comes
from very, very pessimistic assumptions.鈥� He says it is 鈥渁bsurd鈥� to take such a
minuscule maximum probability and multiply it by the number of people who would
die if a strangelet swallowed the world. 鈥淚t鈥檚 not going to happen,鈥� he says.