- The SETI Institute focuses on the Search
for Extraterrestrial Intelligence. There are two key words here: intelligent
and extraterrestrial. If you utter them in the same breath you will be
transformed into Dr. Jekyll and Mr. Hyde. At times they make you sound
like a weirdo, and at other times like an insightful visionary.
- Corbis Tarzan wasn't alone in the world,
but he matured with no idea that people existed
- This is because encountering extraterrestrial
intelligence is highly unlikely in anyone's daily routine, and also highly
suggestive of a person's imagination. For whatever the reason "
psychological, socio-political or purely scientific " the issue of
extraterrestrial intelligence resonates deeply in our minds. But how real
- Picture Tarzan in the middle of the African
jungle with a vine, a fig leaf, and a tree house. His mission: to communicate
with the nearest intelligent beings. So far, chimpanzees have paid him
a measure of attention but he's run out of bananas. Exploration is impractical
because of the density of the vegetation. He's not even certain there's
anyone beyond his neighborhood trunk. So unless he can think of a brilliant
idea, he's stuck babbling with the chimps.
- Our situation in the cosmos isn't unlike
Tarzan's. Humanity is uncertain whether other intelligent species exist
beyond its own planet and exploring nearby systems takes too long compared
to the human life span.
- There are many trees in the jungle, thinks
Tarzan, any one of them might host another tree house or a habitable cavity.
Tarzan will find himself imagining a thousand different kind of tree trunks
and the species living in them. Maybe he'll start counting the number
of trees and speculate on the probability one is inhabited by intelligent
- Astronomers are counting the number of
stars in our galaxy. The latest estimate puts that number at two to three
hundred billion stars. The probability that a stellar system hosts intelligent
life is quite uncertain. The probability that an intelligent species "
if any " is attempting to communicate with us is even more uncertain.
- NASA A galaxy is capable of hosting
millions of intelligent life forms
- There are many unknowns: the percentage
of stars with a planet, of those, how many support life or can, and of
those, would the inhabitants be able to communicate or interested in communication,
and so on. Estimates range from a dozen to a million possible intelligent
extraterrestrial civilizations in the Milky Way Galaxy alone.
- If Earth is any example, one planet out
of nine hosts life, and one species out of billions has a higher intelligence.
Given these numbers, even with 300 billion stars the estimate of advanced
extraterrestrial civilizations is a handful, if that. In fact, given these
numbers it seems highly unlikely that we would even exist. The strongest
argument for intelligent extraterrestrial life is that we are here. This
argument is moot if you believe humanity is special.
- So we speculate on the numbers. One million
advanced civilizations in the Milky Way implies an average separation
on the order of 500 light-years. That is, at the speed of light (One light-year
is the distance traveled in one year at the speed of light or 5.9 trillion
miles. 1 trillion = 1,000 billion) it would take 500 years to send a message
and another 500 to get a reply.
- It is more efficient at this stage of
the game to send waves rather than astronauts to far-flung systems. In
fact, it is even more efficient to plainly listen. SETI is about listening
efficiently and sending messages efficiently.
- In the jungle Tarzan might light a fire,
but there's little chance someone will see it because of the vegetation.
He might try a thousand different things but his best bet is to hit a hollow
tree trunk or scream audibly. The problem is how to distinguish his voice
from all the jungle noise.
- Since the recipient's unique trait compared
to the environment is intelligence, then Tarzan's sound will have to be
intelligent. Possibly, his timbre will follow a mathematical sequence
or represent a universal constant (such as the speed of light). Tarzan
opts for sound inflection, being smart enough to emit his message in the
audible part of the spectrum.
- Because hydrogen is one of the most common
elements in the universe, and it naturally emits at a very specific radio-frequency,
astronomers expect intelligent signals in the neighborhood of that frequency.
So why haven't astronomers detected a greeting message yet?
- Perhaps the answer lies in a recent discovery.
In 1998, a previously unknown tribe of natives was spotted in the Brazilian
jungle. Even with supersensitive satellites and industrial activity barely
60 miles away, we were unaware of their existence for almost the entire
20th century. Likewise, although bombarded by radio and television waves,
they never detected them.
- So whether we are the Amazon natives
of the cosmos, or the advanced civilization we claim to be, one thing is
for certain: It's not because we're alone, that someone isn't out there.