Discovery
Getting a Message Across the Universe: Would E.T. Send a Letter?
Snail mail from outer space
March 10, 2006
The prospect of communicating with intelligent life beyond Earth has
long captured human imagination. For decades, scientists have been
sending hopeful messages in the form of radio signals into space and
patiently scanning the skies for signs that someone, somewhere, is
doing the same.
So far, that search has been fruitless. But we might be wise to look
as well as listen, says Christopher Rose, a physicist and professor of
electrical engineering at New Jersey's Rutgers University. By his
calculations, it's vastly more efficient to send large messages across
space not in the form of radio waves or beams of light, but in physical
packages. That's right: If we want to send a note to outer space, Rose
says, we should consider sending a message in a bottle.
Likewise, we should anticipate messages that might arrive here as
physical artifacts--embedded in a meteorite, perhaps, or falling to
Earth after hurtling across the cosmos on a comet's tail.
Rose and co-author Gregory Wright, a physicist at Antipodes
Associates in Fair Haven, N.J., published that surprising conclusion in
the journal Nature in 2004. But they did not set out to make headlines on the best way to contact "E.T."
Rose's research began with a grant from the National Science
Foundation to study how to make wireless communications on Earth more
efficient. The project's goal, he explains, was to figure out how to
"get the most amount of information across for the least amount of
energy." While investigating that subject, it occurred to him that this
work might have implications for interstellar communications as well.
In wireless communications, transmitting information with radio
waves makes sense because speed is a critical consideration. But in
some instances--such as when two people are just around the corner from
each other--it's more efficient, from an energy conservation
perspective, to simply deliver a letter than to use radio waves or some
other form of electromagnetic energy.
"That was the jumping off point," says Rose. "I thought, 'Huh,
there's a fundamental issue here. When is it better for me to hand over
the information than to radiate it?' And that was the kernel of the
idea."
Rose calculated how much energy would be required to ship a message
1,000 light years into space. A package traveling a million kilometers
an hour (about 670,000 miles per hour) would need a million years to
reach its destination. A radio transmission would get there in only a
fraction of that time--an obvious advantage when the sender can't
tolerate a delay, as in the case of cell phone conversations on Earth.
But when timing is irrelevant, Rose found that sending a physical message makes more sense.
The advantage exists because of the nature of electromagnetic waves.
Although electromagnetic radiation can travel very fast (in the case of
light, about 6.7 million miles per hour), it disperses and weakens
across space. That's why a flashlight beam only shines brightly enough
to see over short distances, and why a parent has to shout more loudly
at her child, the further away the child is.
In other words, the farther a light beam travels, the more it
spreads out. Any message encoded by it will have likewise faded in the
voyage. The same is true for radio waves: For a radio message to retain
its meaning over a long distance, it must be beamed out with high
energy. A message inscribed on an object, on the other hand, remains as
legible when it reaches its destination as on the day it was sent, no
matter how far it has gone.
What's more, once a physical message arrives at a given destination,
it stays there. A radio signal must be intercepted at the moment it
passes by in order to be "received."
While it would take a serious amount of protection--thousands of
pounds of lead, in Rose's estimation--to prevent damage by cosmic waves
in transit, the energy required to package information and hurtle it
across space would be far less than that required to beam out
high-powered electromagnetic signals on a regular basis. The further a
message must go, and the longer the message is, the greater the
advantage of sending that message in a physical form.
The advantage is strong enough, Rose says, to compensate for the
fact that thousands, or even hundreds of thousands, of messages might
need to be sent to cover the range of potential star systems that could
potentially pick up a single radio signal.
If, for instance, we wanted to send a very large message--say, all
of the information inside the Library of Congress--to a star 10,000
light years away, it would be a hundred billion times more efficient to
encode it in silicon chips than it would be to radiate the same amount
of information from the world's largest radio telescope.
The idea of sending physical objects into space is nothing new. When
NASA's Pioneer 10 spacecrafts went plunging into space in 1977, they
carried twin 12-inch disks bearing words, music and images selected by
a team of scientists to represent life on Earth. Now at the edge of the
solar system, the Pioneer 10 crafts may represent the best approach,
says Rose.
Like much good news, however, this discovery comes with a catch: A
physical package could not travel as fast as radio or light waves. At a
reasonable speed, Rose estimates a package could take 20 million years
to reach distant stars. That's but a blip in time, given the galaxy's
10 billion-year history, but it doesn't inspire hope for the kind of
"contact" made famous by Jodie Foster in the movie of the same name.
For simple messages meant to convey only "I am here," Rose says
radio waves are still more efficient. And because radio waves travel so
quickly, they offer the possibility of two-way communication. So the
efforts of researchers looking for signals with giant radio
telescopes--like those at the California-based SETI Institute--are
worthwhile, he says.
Still, says Rose, there's something to be said for sending a message
out for "posterity," and for devising ways to look for physical
messages that other life forms may have shipped across space, hoping to
find us.
Rose's Nature paper was the first quantitative comparison
of the costs of the different ways of delivering information across
space. Since then, Rose has been working on the next logical question:
If sending a physical message is the most efficient way to communicate,
in what form might these message arrive, and how should we look for
them?
He stops short of guesswork, though, preferring not to speculate
about what an extraterrestrial life form might say or why it might want
to communicate with people in the first place. For Rose, it's not about
psychology or science fiction: "It's just the physics, ma'am."
--Sarah Goforth
Investigators
Christopher Rose
Roy Yates
Related Institutions/Organizations
Rutgers University New Brunswick
Locations
New Jersey
Related Programs
Communications Research
Related Awards
#9973012 Interference Avoidance In Wireless Systems
Total Grants
$430,003 Related Websites
Christopher Rose's page on Cosmic Communications: http://www.winlab.rutgers.edu/~crose/cgi-bin/cosmicB.html
The Rutgers Wireless Information Network Laborator: http://www.winlab.rutgers.edu/pub/Index.html
NSF's Communications Research Program: http://www.nsf.gov/funding/pgm_summ.jsp?pims_id=5200
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