Researchers: ET should write, not call
By Robert Roy Britt
SPACE.com
Thursday, September 2, 2004 Posted: 4:04 PM EDT (2004 GMT)
(SPACE.com)
-- A fresh perspective on searching for aliens suggests ET is more likely
to send us something akin to a message in a bottle rather than relying on
energy-intensive, inefficient radio messages.
The professional
hunt for ET depend largely on huge telescopes that scan for electronic intelligence
in the ether, on the assumption that an brainy, technologically advanced
civilization might try to reach out to others, or that their communications
would leak into space.
But sending a signal across the cosmos is expensive
an inefficient, argues Christopher Rose, a professor of electrical and computer
engineering at Rutgers University. The idea is detailed in the August 25
issue of the journal Nature.
Tortoise and hare
Rose
and physicist Gregory Wright initially set out to learn how to send the most
information over a wireless channel. They then considered the amount of energy
needed to send a signal over greater distances. As logic suggests, more energy
is needed to send a message farther, and the signal weakens.
Radio
waves, laser beams or X-ray pulses and other electromagnetic signals all
travel at the speed of light. But the farther they go, the more they disperse.
That makes them harder to detect.
"Think of a flashlight beam," Rose said. "Its intensity decreases as it gets farther from its source."
Seth
Shostak knows about this problem. Shostak worked on the SETI Institute's
Project Phoenix, a just-finished search for extraterrestrial radio signals
(they didn't hear any) that was the most comprehensive so far. Not involved
in Rose's research, Shostak wrote recently that sending a barely detectable
radio-based signal across 100 light-years and in all directions would require
100 billion watts of power. Translation: You'd have to focus the output of
all American power planets to do the job.
Interstellar radio programs
face another problem in garnering listeners. Once an electronic signal passes
its intended recipient, it is gone for good. If the creatures on a target
planet have their electronic ears tuned to some other frequency when a signal
arrives, or if they have yet to develop the right listening technology, the
effort to make contact is wasted.
A written message in a space capsule,
however, could have landed on Earth millennia ago and await discovery. And
a spacecraft, once up to speed, can cruise for long periods with little additional
power input.
Time to spare?
The
downside to the message-in-a-bottle approach: Human technology, at least,
can't propel a spacecraft to even a significant fraction of light-speed.
So getting a note from one star system to the next would take more generations
than the average human mind can contemplate.
The most distant probe
sent by earthlings is Voyager 1, just crossing the outer boundary of the
solar system. After a 27-year journey it is 90 times the distance from Earth
to the Sun, or nearly 8.4 billion miles (13.5 billion kilometers). A radio
signal can go that far and back in about a day.
The next nearest stars,
in the Alpha Centauri system, are 4.3 light-years distant. That's more than
3,000 times what Voyager has so far covered.
However, so long as time
is not of the essence, Rose and Wright figure hard copy would be the preferred
method to talk across the stars.
"If haste is unimportant, sending
messages inscribed on some material can be strikingly more efficient than
communicating by electromagnetic waves," Rose said.
Outbound examples
Further, he points out, long messages are handled more efficiently by inscription.
NASA's
two Voyager probes exhibit such an effort. Each carries a 12-inch, gold-plated
copper disk with sounds and images that portray terrestrial life and culture.
The cost to send the records was practically inconsequential to the overall
price tag of the mission, whose main purpose was to study the planets.
Radio pulses announcing anything more than "we exist" would consume more energy (which requires money) for every word.
Rose
is not against listening. He just thinks looking might prove more fruitful.
He also notes that messages might not arrive as language, per se. Perhaps
organic material embedded in an asteroid, the Moon or a satellite of Jupiter
would reveal the presence of life elsewhere. That of course is not a new
idea. Other scientists have considered that unintelligent (microbial) life
could even travel between planets embedded in a rock kicked up by an asteroid
impact. No calling card required.
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