SETI, the Search for Extra-Terrestrial Intelligence, is now more than fifty years old. In 1959, the Cornell physicists Giuseppi Cocconi and Philip Morrison published an article in the journal Nature proposing the idea that it might be possible to use microwave radio to communicate between the stars. The next year, in 1960, Frank D. Drake, a radio astronomer at the National Radio Astronomy Observatory in Green Bank, West Virginian carried out the first attempt to detect such interstellar radio transmissions. Drake named this first attempt Project Ozma, after the Queen in L. Frank Baum’s land of Oz. Oz, he said, was a place “very far away, difficult to reach, and populated by strange and exotic beings.”
Drake chose to listen to two nearby stars, Tau Ceti, which is located in the Constellation Cetus and Epsilon Eridani in the Constellation Eridanus. They are both about 11 light years away and are similar to the sun in age and brightness.
Unfortunately, no radio waves were actually detected during the time that Drake listened to those two stars, from April through July of 1960. Of course, he only listened to one channel during that time, the 1420 MHz line of neutral hydrogen because of its supposed astronomical significance. In fact, no artificial radio waves have ever been detected from anywhere in the sky during any SETI project.
The first scientific conference devoted to SETI research took place at Green Bank, West Virginia the next year, in 1961. Later, throughout the 1960’s, the Soviet Union performed a number of searches with omnidirectional antennas in the hope of picking up powerful radio signals. In 1966, American astronomer Carl Sagan and Soviet Astronomer Iosif Shklovskii wrote the pioneering book in the field entitled, Intelligent Life in the Universe.
In 1971 NASA funded a SETI study that involved Rake, Bernard Oliver of Hewlett-Packard Corporation and others. The resulting report proposed the construction of an Earth-based radio array with 1500 dishes known as Project Cyclops. The array was never constructed.
In 1974, after a major renovation of the radio dish, a largely symbolic attempt was made at the Arecibo Observatory in Puerto Rico to send a message to other worlds. It was aimed at the globular star cluster M13, which is 25,000 light years away. If that message is detected by anyone out there, we still have about 50,000 years to wait before we’ll receive their reply.
Most SETI research in the United States has been done by universities and private organizations. For one year in 1992 the U.S. Government funded the NASA Microwave Observing Program (MOP) which was planned as a long-term effort to conduct a general survey of the sky and to carry out targeted searches of 800 specific nearby stars. Congress soon eliminated the funding, but the project was resurrected by the nonprofit organization, the SETI Institute of Mountain View, California. MOP was renamed Project Phoenix and was directed by Jill Tartar. Project Phoenix observed about 800 stars over the frequency range of 1200 to 3000 MHz from 1995 through March, 2004. The search was sensitive enough to pick up alien transmissions of a gigawatt or more up to a distance of about 200 light years. The Arecibo message of 1974 was sent at that power level, for instance.
Today, the SETI Institute is still busy. It is collaborating with the Radio Astronomy Laboratory at UC Berkeley to develop a specialized radio telescope array for SETI studies. It is called the Allen Telescope Array, named after Paul Allen, the project’s primary financial benefactor. Paul Allen was a founder of Microsoft and he financed SpaceShipOne, which won the Ansari X-Prize in 2004. When completed, the full radio telescope array will consist of 350 or more radio dishes, each about twenty feet in diameter. The first portion of the array, made up of forty-two dishes, became operational in October, 2007. Unlike the first Ozma search in 1960, the Allen Telescope Array monitors hundreds of millions of radio channels all at once.
Detecting signals at interstellar distances will not be easy to accomplish. And even if there are civilizations out there, they may not be purposely transmitting. For instance, the Earth has been radiating radio signals, radar, and television signals for more than seventy years now, meaning that the earliest signals form a bubble out from Earth seventy light years in diameter, enveloping hundreds of stars. However, even if there were a civilization similar to ours within that distance of Earth, none of the SETI instruments currently operating would be able to detect such radio or television signals. At interstellar distances, they are just too weak to separate from all the more noisy radio signals put out by stars, dust and gas. They are lost in the static.
This is not to say that SETI is a waste of time, however. But it is to say that the absence of any detectable transmissions from beyond Earth thus far doesn’t prove that no one is out there. Given the size of the universe, it would seem an awful waste of real estate if we really are the only intelligent beings in it.