Extraterrestrial Life and Intelligence
Who's out there? Are we alone in the universe?
Scientists involved in SETI
— the Search for ExtraTerrestrial Intelligence
— are using modern technology to search for the answer to this fundamental
They listen for a signal from space. This arises more questions:
How do we know if a signal is from ET? And: what happens if we find
There is more than science
fiction and the X files to the search for extraterrestrial life
Over the last years,
scientists have developed a theory of cosmic evolution that predicts
that life is a natural phenomenon likely to develop on planets with
suitable environmental conditions. Scientific evidence shows that
life arose on Earth relatively quickly, suggesting that life will
occur on similar planets orbiting sun-like stars. With the recent
discoveries of extrasolar planetary systems, and the suggestive
evidence that life may once have existed on Mars, this scenario
appears even more likely.
The central question
of SETI science is not: "Is someone hiding aliens?"
But rather: "What is Drake equation ?"
This equation has played a more crucial role in SETI than an entire
season of X files broadcasts ...
This equation aims at
roughly estimating the number of (technological) civilizations that
might exist in the space.
In 1961, while working as a radio astronomer, Frank Drake conceived
an approach to bound the terms involved in estimating the number
of technological civilizations that may exist in our galaxy. The
identifies specific factors thought to play a role in the development
of such civilizations. Although there is no unique solution to this
equation, it is a generally accepted tool used by the scientific
community to examine these factors.
N = R* × fp × ne × fl × fi × fc × L
N = The number of communicative civilizations The number of
civilizations in the Milky Way Galaxy whose radio emissions are
R* = The rate of formation of suitable stars The rate of formation
of stars with a large enough "habitable zone" and long enough lifetime
to be suitable for the development of intelligent life.
fp = The fraction of those stars with planets The fraction of
Sun-like stars with planets is currently unknown, but evidence indicates
that planetary systems may be common for stars like the Sun.
ne = The number of "earths" per planetary system All stars have
a habitable zone where a planet would be able to maintain a temperature
that would allow liquid water. A planet in the habitable zone could
have the basic conditions for life as we know it.
fl = The fraction of those planets where life develops Although
a planet orbits in the habitable zone of a suitable star, other
factors are necessary for life to arise. Thus, only a fraction of
suitable planets will actually develop life.
fi = The fraction life sites where intelligence develops Life
on Earth began over 3.5 billion years ago. Intelligence took a long
time to develop. On other life-bearing planets it may happen faster,
it may take longer, or it may not develop at all.
fc = The fraction of planets where technology develops The fraction
of planets with intelligent life that develop technological civilizations,
i.e., technology that releases detectable signs of their existence
L = The "Lifetime" of communicating civilizations The length
of time such civilizations release detectable signals into space.