by Frank Drake in 1961, The Drake Equation provides a way to determine
how many intelligent and communicating civilizations are present in our
The Drake Equation is
not “an end in itself” but provides a number of questions which need
order to reach an accurate conclusion – as we learn more from such
subjects as astronomy, biology etc…, our ability to answer
the questions will be enhanced.
The Drake Equation is:
= N* fp ne fl fi fc fL
N* represents the
number of stars in the Milky Way Galaxy
Question: How many
stars are in the Milky Way Galaxy?
estimates are 100 billion.
fp is the fraction of
stars that have planets around them
percentage of stars have planetary systems?
estimates range from 20% to 50%.
ne is the number of
planets per star that are capable of sustaining life
Question: For each star
that does have a planetary system, how many planets are capable of
estimates range from 1 to 5.
fl is the fraction of
planets in ne where life evolves
Question: On what
percentage of the planets that are capable of sustaining life does life
estimates range from 100% (where life can evolve it will) down to close
fi is the fraction
of fl where intelligent life evolves
Question: On the
planets where life does evolve, what percentage evolves intelligent
Answer: Estimates range
from 100% (intelligence is such a survival advantage that it will
certainly evolve) down to near 0%.
fc is the fraction of
fi that communicate
percentage of intelligent races have the means and the desire to
Answer: 10% to 20%
fL is fraction of the
planet's life during which the communicating civilizations live
Question: For each
civilization that does communicate, for what fraction of the planet's
life does the civilization survive?
Answer: This is the
toughest of the questions. If we take Earth as an example, the expected
lifetime of our Sun and the Earth is roughly 10 billion years. So far
we've been communicating with radio waves for less than 100 years. How
long will our civilization survive? Will we destroy ourselves in a few
years like some predict or will we overcome our problems and survive for
millennia? If we were destroyed tomorrow the answer to this question
would be 1/100,000,000th. If we survive for 10,000 years the answer will
When all of these
variables are multiplied together when come up with:
N, the number of
communicating civilizations in the galaxy.
– a brief biography.
in Chicago on May 28th, 1930 to Richard and Winifred Drake and raised in
Chicago's South Shore with sister, Alma, and brother, Robert, Frank
Drake became interested in science at an early age.
He and his friends
passed their time experimenting with motors, radios, and chemistry sets.
He was very interested in astronomy and he soon began to consider the
actual size of the universe and the possibility of the existence of
other planets and life on other planets. This seemed quite possible to
him but because of the religious convictions of his parents and teachers
he had little chance to discuss the subject of extraterrestrial life.
After high school Drake
enrolled at Cornell on an ROTC scholarship to study electronics. It was
here that he fell in love with astronomy and finally found someone else
who was considering the possibilities of life on other planets.
In 1951, during his
junior year he attended a lecture by Otto Struve, one of the world's
preeminent astrophysicists. Struve showed that there was mounting
evidence that planetary systems had most likely formed around half of
the stars in the galaxy, stating that life could certainly exist on some
of those planets. Drake realised that he had found someone who shared
Drake then served for
three years with the Navy to repay his scholarship and became the
officer on the USS Albany where he became highly skilled operating and
fixing the latest high tech electronic equipment.
Following his stint in
the navy, Drake attended Harvard graduate school to study optical
astronomy, the only summer position available being in radio astronomy.
His electronics experience in the Navy made him a “good man for the job”
as the radio astronomy equipment was constantly in need of tweaking and
repair. Drake became totally fascinated with radio astronomy.
After graduate school
in 1958 he got a position at the newly founded National Radio Astronomy
in Green Bank, West Virginia and in 1960 the first search took place.
This search was called “Project Ozma” by Drake,comprising of a two week
observation of the stars Tau Ceti and Epsilon Eridani. During the search
a false alarm, which turned out to be a terrestrial signal, caused some
excitement but other than that no signals were detected. Drake was not
In 1961 Drake and J.
Peter Pearman, an officer on the Space Science Board of the National
Academy of Sciences, organized the first SETI conference. The meeting,
held at the NRAO, comprised of a dozen or so scientists who were
interested in SETI and lasted 3 days.
Drake came up with the
now famous Drake Equation whilst preparing for this conference. Frank
Drake was primarily interested in the detection of planetary systems and
life, particularly intelligent life elsewhere in the universe and he
participated in Project Phoenix, the most powerful system for searching
for radio signals from other civilizations, employing radio
spectrometers that can monitor up to 15
million frequency bands simultaneously, on two polarizations, as well as
special signal detection instruments and software to search for a
variety of possible intelligent signal forms in the captured data.
Being portable, the
system can be transported to the world's largest radio telescopes, all
over the world and is being used to search for intelligent signals from
some 1,000 of the nearest solar-type stars and from star-rich regions of
the Milky Way..