Numerous challenges exist in the search for life outside the Solar System. In order to search for a radio signal that could be classified as intelligent, most SETI projects make certain assumptions about what that signal will be like and where it will originate from. As a result, there has not yet been a truly comprehensive SETI search because searching for a radio signal from an alien civilization requires answers to as yet unanswerable questions.
Early SETI Experiments
In 1960, a Cornell University astronomer named Frank Drake conducted the first SETI experiments. He used a 26 metre radio telescope in Green Bank, West Virginia to listen to radio waves generated by the stars Tau Ceti and Epsilon Eridani. In 1971, NASA, in cooperation with Drake and several other astronomers conducted a study in which they proposed an array of more than 1,500 radio telescopes called Project Cyclops. Even though Project Cyclops was never built, it still had an influence on the thinking of SETI researchers and radio astronomers as well as on radio telescope design.
SETI and the Allen Telescope Array
For the past several years, the SETI Institute has been collaborating with the Radio Astronomy Lab at UC Berkeley, California. Their goal is to build a telescope array dedicated solely to SETI research. When completed, the Allen Telescope Array will consist of more than 350 individual dishes. Collectively, they will have the sensitivity of a single radio telescope 300 feet in diameter. As of September, 2007, 42 of the proposed 350 dishes have been built. Continued funding and the completion of the project is dependant up the performance of the 42 dishes that comprise the first phase of construction.
Optical SETI Searches
Some astronomers have considered the idea of searching for alien civilizations optically. Some astronomers have recently begun to consider the possibility that a sufficiently advanced civilization might use high powered lasers as a means of interplanetary communication.
There are two problems with this type of SETI search, however. The first problem is that lasers are monochromatic. This means that a laser is tuned to one particular part of the electro-magnetic spectrum. As a result it can only be seen by a telescope that is also tuned to that part of the spectrum. It has been suggested that an alien civilization seeking to make contact with other civilizations might utilize a variable system of laser pulses across a broad range of frequencies, increasing the odds of detection.
The second problem is that lasers are highly directional. They can also be blocked from our view by clouds of interstellar dust. As a result, Earth would have to be directly in the line of fire.
Where Are They?
In the 1950s, Italian physicist Enrico Fermi suggested that technologically advanced civilizations are common in the Milky Way Galaxy. If this is the case, then they should be easily detectable. “Where are they?” he asked.
One possible explanation for this apparent paradox is that while, primitive life is very common, complex intelligent beings are very rare.
However, as the number of extra-solar planets continues to grow, including a number of near Earth-sized planets, increasing attention is being given to the study of extraterrestrial life.
Works CitedSagan, Carl; Iosif Shklovskii (1966). Intelligent Life in the Universe
"SERENDIP". UC Berkeley. . Retrieved on Feb.24/09
Terdiman, Daniel. SETI's large scale telescope scans the skies. Cnet News. Published Dec.12/08. Downloaded Feb.24/09
Terdiman, Daniel and Isaac Gray.Searching the heavens for life. Cnet News. Published Dec. 12/08. Dowloaded. Feb.24/09
Exers, Ronald, D. Cullers, J. Billingham, L. Scheffer (editors) (2003). SETI 2020: A Roadmap for the Search for Extraterrestrial Intelligence. SETI Press.
Eric Jones, "Where is everybody?", An account of Fermi's question", Los Alamos Technical report LA-10311-MS, March, 1985.
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