Intelligent Life in the Universe
"The Universe is populated by innumerable suns, innumerable earths, and perhaps, innumerable forms of life. That thought expresses the essence of the Copernican revolution. No revelation more striking has ever come from the scientific mind."
Robert Jastrow
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Frank Drake
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Classroom discussions about extra-terrestrial intelligent life typically begin with
an introduction to the Drake Equation. It was developed by Frank Drake in 1961
in order to codify the important factors that can be multiplied to determine
how many intelligent, communicating civilizations there are in our galaxy.
The Drake Equation
N =
R*
fp
ne
fl
fi
fc
L
R* is the total number of stars in the Milky Way Galaxy
fp is the fraction of stars that have planets around them.
ne is the number of planets per star that are capable of sustaining life.
fl is the fraction of planets in ne where life evolves.
fi is the fraction of fl where intelligent life evolves.
fc is the fraction of fi that communicate.
L is fraction of the planet's life during which the communicating civilizations live and attempt contact.
The resulting product, N, is the total number of communicating civilizations in the galaxy.
The amazing thing about the Drake Equation is that no matter how conservative you are
with the values of the individual factors, it leads to an incredibly large number of beings
out there, with radios, attempting to contact one another. Human attempts to connect with
a galactic community are only fledgling. The most famous and organized effort is called
SETI (Search for Extraterrestrial Life) which was founded by Frank Drake in 1961.
Anyone with an Internet connection can now join the effort by lending their
computer's idle time to analyzing radio signals from space in the hopes of finding
unnatural patterns. The computer sharing program is administrated by
SETI@HOME
at University of California Berkeley.
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Carl Sagan 1934 - 1996
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Carl Sagan Center for the Study of Life in the Universe
Named for the famous popularizer of astronomy,
SETI has created this team of diverse
researchers in a interdiciplinary field called "astrobiology."
Supporting institutions included NASA, the National Science Foundation, and major
universities. Research includes such related areas as
Astronomy, Chemical evolution, Origin of life, Biological evolution
Cultural Evolution, and active search for extraterrestrial intelligence.
Carl Sagan conceived the idea of a attaching a universal message to a spacecraft
destined to leave the solar system which might be understood by extraterrestrials that find it.
He succeeded in delilvering that message to interstellar space in the form of plaques,
attached to the space probes Pioneer 10 launched in 1972 and Pioneer 11 launched in 1973.
The message was designed to encode the most information possible in minimal space.
At the top is a diagram representing the hyperfine transition of neutral hydrogen. This is meant to convey
a unit of length (21 cm) which is used to indicate measurements elsewhere in the message.
The radial lines emanating
from a point show the relative distances to 14 pulsars from our Sun and the distance to
the galactic core.
This could conceivably be used by a clever species to identify our Sun's
location within the Milky Way Galaxy. A tick mark at the end of each line gives the Z coordinate
perpendicular to the galactic plane. The pulse rate of the pulsars is included, and since pulsars
slow their pulsing at a predictable rate, a successful decoding of the placque would also indicate
precisely "when" the spacecraft was launched. The image also includes a diagram of our solar system,
the spacecraft's route out of the solar system, and a silhouette of the craft itself.
UFO's, Alien Abductions, & Crop Circles
As exciting and as entertaining as the stories are,
astronomers as a group place very low confidence in theories that include
visitation to Earth by extraterrestrials. There are two main reasons for this skepticism.
First of all, with thousands of anecdotes of contact, there should be at least
one sample of empirical evidence; something besides hearsay. Second, astronomers
appreciate the extent of the problem of the vastness of space and time. It is an axiom
that there is much we don't know. But if beings
adventured across the void to find us here, then they likely left home long before
we even existed. This would be an astonishing coincidence, especially if their
objective was to vandalize our corn.
So here is the conundrum. Any beings truely intelligent enough
to make the trip, would know enough to call first. Calling first is cheap, and polite.
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ASTRO 101
