interpretive challenges
pynchonoid
pynchonoid at yahoo.com
Fri May 9 19:19:21 CDT 2003
Public release date: 7-May-2003
Contact: Claire Bowles
claire.bowles at rbi.co.uk
44-207-331-2751
New Scientist
Are aliens hiding their messages?
IF WE are not alone in the Universe, why have we never
picked up signals from an extraterrestrial
civilisation? This long-standing puzzle, known as the
Fermi paradox after physicist Enrico Fermi, who first
posed the question, is still one of the strongest
arguments against the existence of intelligent aliens.
But two physicists have come up with an intriguing
solution. They suggest a way in which aliens could
send messages to each other across space that not only
disguises their locations but also makes it impossible
for a casual observer to even distinguish the messages
from background noise. Messages sent by this method
could be criss-crossing our Galaxy without us ever
knowing.
At first glance, sending a message without giving away
your location appears impossible. If a signal - a
stream of photons - comes from a single source, its
origin can always be determined by measuring the
direction of recoil of a detector struck by the
photons. But Walter Simmons and his colleague Sandip
Pakvasa from the University of Hawaii at Manoa have
come up with a cunning way around this.
The signaller splits the message into two parts, so
that the photons are sent in opposite directions to
mirrors located far from the home planet. The mirrors
redirect the signals to the intended receiver, who
recombines the photons to reconstruct the message (see
Graphic).
The key idea is that the message is encoded not by the
pattern or sequence of photons sent over time, but by
their positions in space. For example, this can be
done by shining the light beam through a stencil.
If the image is tiny enough, Heisenberg's uncertainty
principle - which limits the amount of information
that can ever be known about a microscopic particle -
means that measuring the position of the photons makes
it impossible to gain accurate information about the
direction in which they are travelling. So if you
detected the message, it would be impossible to
determine the origin of the two beams. "The mere act
of reading the message introduces enough uncertainty
to make it useless for direction-finding," explains
Simmons.
Neither the intended receiver nor any eavesdropper
would be able to locate the home planet of the sender.
What's more, it would be impossible to detect the
message at all without extremely sophisticated
technology. In order to recombine the beams and
recreate the message you would need to detect the
arrival time of the photons extremely accurately to
identify pairs of photons split by the sender. "Such
photons are distinguishable from the background of
stellar photons because they arrive very close
together in time," says Simmons. "But any
eavesdropper, like us, might not realise this and see
only the background."
"The proposal is ingenious," says Jonathan Rosner, a
physicist at the Enrico Fermi Institute in Chicago,
although he says it is hard to tell if the method
could work in practice. Paul Shuch, director of the
SETI League in New Jersey, also points out that being
able to disguise a sender's location would be
extremely useful for secure military communications
here on Earth. "In a few decades, when it's
declassified, we may well find that such a technique
is already in use."
###
Marcus Chown
UK CONTACT - Claire Bowles, New Scientist Press
Office, London:
Tel: 44-207-331-2751 or email claire.bowles at rbi.co.uk
US CONTACT - Michelle Soucy, New Scientist Boston
Office:
Tel: 617-558-4939 or email
michelle.soucy at newscientist.com
New Scientist issue: 10 May 2003
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