S.E.T.I.

SETI is an acronym for the Search for Extraterrestrial Intelligence. It is the science of using telescopes, radio, and optical, to search the skies for signals from alien civilizations.

The idea of SETI began in 1959 with the publication of a paper in the British journal Nature by Giuseppe Cocconi and Philip Morrison. The paper discussed the possibility of the existence of alien civilizations and how we might be able to detect them. Their conclusion was that the easiest method of detection would be radio waves.

Radio waves were chosen because they are capable of traveling the vast distances between stars and can be generated with reasonable amounts of power. We have been sending radio waves out into space for more than sixty years. All of our radio, TV, satellite, and radar signals are currently spreading out throughout the galaxy. Perhaps they've already been detected by someone.

At the same time as Cocconi and Morrison's paper was published a young astronomer named Frank Drake was putting together plans for the first search. The search, named Project Ozma, was conducted in 1960. Over a two week period the stars Tau Ceti and Epsilon Eridani were scanned for alien signals. No signals were found but the search had begun.

In the 30 years since the initial Ozma search many others have been carried out with more sensitive equipment, over much longer time frames, observing thousands of other stars. So far no alien signals have been detected but we've really only begun to scratch the surface. There are an estimated 100 billion stars in the Milky Way galaxy alone! To complicate matters further there are millions of frequencies that a signal could be received on. It may be that we just haven't looked in the right place at the right time yet.

The Drake Equation was developed by Frank Drake in 1961 as a way to focus on the factors which determine how many intelligent, communicating civilizations there are in our galaxy.

Drake's Equation

N = N* fp ne fl fi fc fL
The equation can really be looked at as a number of questions:

N* represents the number of stars in the Milky Way Galaxy
Question: How many stars are in the Milky Way Galaxy?
Answer: Current estimates are 100 billion.

fp is the fraction of stars that have planets around them Question: What percentage of stars have planetary systems?
Answer: Current 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 sustaining life?
Answer: Current 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 actually evolve?
Answer: Current estimates range from 100% (where life can evolve it will) down to close to 0%.
fi is the fraction of fl where intelligent life evolves Question: On the planets where life does evolve, what percentage evolves intelligent life?
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 Question: What percentage of intelligent races have the means and the desire to communicate?
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 be 1/1,000,000th.

When all of these variables are multiplied together we come up with:

N, the number of communicating civilizations in the galaxy.

The real value of the Drake Equation is not in the answer itself, but the questions that are prompted when attempting to come up with an answer. Obviously there is a tremendous amount of guess work involved when filling in the variables. As we learn more from astronomy, biology, and other sciences, we'll be able to better estimate the answers to the above questions.

Try The Equation

For each variable choose what you think is the best answer from the combo box. After you've chosen all your answers press the calculate button and see how many communicating civilizations you think there are in the galaxy.

N* = the number of stars in the Milky Way galaxy:

fp = fraction of stars with planets around them:

ne = number of planets per star ecologically able to sustain life:

fl = fraction of those planets where life actually evolves:

fi = the fraction of fl that evolves intelligent life:

fc = the fraction of fi that communicates:

fL = the fraction of the planet's life during which the communicating civilizations survives:

N = the number of communicating civilizations in the galaxy =

SETI@home is a scientific experiment that harnesses the power of hundreds of thousands of Internet-connected computers in the Search for Extraterrestrial Intelligence (SETI). You can participate by running a free program that downloads and analyzes radio telescope data. There's a small but captivating possibility that your computer will detect the faint murmur of a civilization beyond Earth.

You can participate in the actual search!
Link to SETI@home

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