- Joined
- Oct 6, 2002
- Location
- Germany NRW
"Alien Landscape." Painting copyright 1998 Lynette Cook.
In 1961 astronomer Frank Drake wrote the
equation that put the search for alien
civilizations on a scientific footing and
launched the modern SETI movement.
How do the numbers look today?
Searching for extraterrestrial life has become a hot topic among astronomers, biologists, and the general public. But not many remember how the subject was jump-started more than 40 years ago.
In September 1959, physicists Giuseppe Cocconi and Philip Morrison published a landmark article in the British weekly journal Nature with the provocative title, "Searching for Interstellar Communications." Cocconi and Morrison argued that radio telescopes had become sensitive enough to pick up transmissions that might be broadcast into space by civilizations orbiting other stars. Such messages, they suggested, might be transmitted at a wavelength of 21 centimeters (1,420.4 megahertz). This is the wavelength of radio emission by neutral hydrogen, the most common element in the universe. Other intelligences might see this as a logical landmark in the radio spectrum where searchers like us would think to look.
Seven months later, radio astronomer Frank Drake became the first person to start a systematic search for intelligent signals from the cosmos. Using the 25-meter dish of the National Radio Astronomy Observatory in Green Bank, West Virginia, Drake listened in on two nearby Sunlike stars: Epsilon Eridani and Tau Ceti. His Project Ozma (named for L. Frank Baum's story Ozma of Oz) slowly scanned frequencies close to the 21-cm wavelength for six hours a day from April to July 1960. The project was well designed, cheap, simple by today's standards, and unsuccessful.
...
In 1960 Frank Drake used this 25-meter radio telescope at Green Bank, West Virginia, to carry out Project Ozma, the world's first systematic search for alien radio transmissions.
However, 40 years of SETI have failed to find anything, even though radio telescopes, receiver techniques, and computational abilities have improved enormously since the early 1960s. Granted, the "parameter space" of possible radio signals (the possible frequencies, locations on the sky, signal strengths, frequency drift rates, on-off duty cycles, etc.) is vastly larger than the tiny bit that has yet been searched. But we have discovered, at least, that our galaxy is not teeming with very powerful alien transmitters continuously broadcasting near the 21-centimeter hydrogen frequency. No one could say this in 1961.
Have we overestimated the values of one or more of the Drake parameters? Is the average lifetime of technological civilizations short? Or have astronomers overlooked some other, more subtle aspect?
get the Full and very interesing Story at SKY@Telescope
Sir Ulli
