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With its 1,000-foot reflector dish, the Arecibo Observatory in Puerto Rico is the world's largest single-dish radio telescope and most powerful radar. Frank Drake used it in 1974 to send the first CETI message. Credit: NAIC/Arecibo Observatory/NSF |
The desire to contact intelligent
life on other planets is much older than the UFO craze and the SETI movement.
Several 19th century scientists contemplated how we might communicate with
possible Martians and Venusians.
These early proposals - which
predate by 150 years the first extraterrestrial message that was sent in 1974 -
were based on visual signals, as the invention of radio was still decades away.
In fact, as history shows, ideas
for interplanetary communication have largely been driven by whatever the
current technology allowed - be it lamps, radios or lasers.
"You go with what you
know," said Steven Dick, NASA Chief Historian.
Are we alone?
Over two thousand years ago, the
ancient Greeks argued over the existence of life
on other planets, but the idea really took off after the Copernican
revolution.
"Once it was realized that all
the planets go around the sun, it was not hard to imagine that the other
planets could be like Earth," Dick said.
Galileo, Kepler and others
considered the inhabitability of the planets, while being careful not to upset
Church authority.
"The idea blossomed in the 17th
century into the 'plurality of worlds' debate, but it remained
controversial," said Dick, who has written several books on the topic.
One of the most influential
proponents for extraterrestrial life was Bernard le Bovier de Fontenelle, who
wrote Conversations on the Plurality of Worlds in 1686.
Despite the interest, there was no
recorded discussion of how we might locate or contact these potential aliens
until more than a century later.
Crop triangles and burning canals
Florence Raulin-Cerceau of the
Alexandre Koyr? Center in Paris has documented the early attempts at
communication with extraterrestrial intelligence (CETI), or what is now
often called active SETI.
"As early as the 19th century,
inventors imagined "sky telegraph" equipment to communicate with the
supposed inhabitants of the solar system's planets," Raulin-Cerceau
recently wrote with her colleague in the French magazine Pour la Science.
The first of these inventors was Carl
Friedrich Gauss, the German mathematician. In the 1820s, he spoke of reflecting
sunlight towards the planets with his land surveying invention, the heliotrope.
He is also credited with the idea of cutting a giant triangle in the Siberian
forest and planting wheat inside.
"The size and color contrast
should have made the object visible from the moon or Mars, and the geometric
figure could only be interpreted as an intentional construction,"
Raulin-Cerceau wrote.
Twenty years later, the astronomer
Joseph von Littrow came up with a similar idea to pour kerosene into a
30-kilometer-wide circular canal that would be lit at night to signal our
presence.
Concentrated light
The second half of the 19th century
saw more realistic proposals, according to Raulin-Cerceau.
In 1869, the French inventor and
poet Charles Cros imagined using a parabolic mirror to focus the light from
electric lamps towards Mars or Venus. He figured the light could be flashed on
and off to encode a message.
"Cros granted that the planets
could be inhabited by beings not able to respond, but he was still persuaded
that 'the eternal isolation of the spheres [will be] vanquished,'" wrote
Raulin-Cerceau.
A light-based "Morse code"
was also considered by the British statistician Francis Galton in 1896. He took
care not to assume that Martians would have our same base-10 counting system,
as they probably wouldn't have 10 fingers.
Around the same time, A. Mercier, a
member of the Astronomical Society of France, devised a plan to place several
reflectors on the Eiffel Tower that could direct sunlight towards Mars. He also
considered using the moon as a giant screen on which to project light beams.
Could aliens have seen any of these
light displays?
"It depends on how much money
you think the Martians are spending on their telescopes," said Seth
Shostak of the SETI Institute.
Radio turns on
It is now generally assumed that
radio is a more suitable means of extraterrestrial communication. Radio waves
are less affected by cosmic dust than visible light, and there is less of a
radio background to deal with in the sky.
Two of radio's pioneers showed
interest in interplanetary radio communication. In 1901, Nikola Tesla reported
receiving a strange signal, possibly from Mars, on his giant transmitting tower
in Colorado Springs. Nineteen years later, Guglielmo Marconi told reporters
about his detection of radio emissions that appeared to come from outer space.
However, the switch to radio-based
SETI did not happen immediately.
As late as the 1920s, many people
(including Albert Einstein) still considered visual-based communication more
practical, since radio transmitters were not yet capable of focusing a beam on
a distant planet.
What's more, scientists gradually
became convinced that Mars did not have the right conditions to support life,
so any presumed extraterrestrials likely lived much, much further away.
"It seemed hopeless to receive
messages from other stellar systems, so people said 'Forget it.'" Shostak
explained.
It wasn't until 1959 that radio-based
SETI started to be taken seriously. In that year, Giuseppe Cocconi and Philip
Morrison showed that radar transmitters of the time were already powerful
enough to send signals many light years through space.
"If we can do it, then the
aliens might be doing it," Shostak said.
In the year that followed, Frank
Drake performed Project Ozma, the first radio sky survey to look for
intelligent signals.
And then in 1974 - a century and
half after Gauss - Drake transmitted the first actual SETI message using the
Arecibo radio telescope. Scientists are still waiting for a response.
- The
Search for Life in the Universe
- The
Man to Contact
- Video
- Listening for Life

