Shostak told a crowd at SETIcon last weekend in Santa Clara that "I actually think the chances that we'll find ET are pretty good. Young people in the audience, I think there's a really good chance you're going to see this happen."
Determining how many alien civilizations exist is the point of the Drake equation, named after Mountain View's own SETI (Search for Extra-Terrestrial Intelligence) Institute-employed luminary Frank Drake. The equation takes into account factors such as how quickly stars form, how many planets are habitable and how long it takes for radio messages to travel in space.
Because many of those factors are unreliable, answers to the question are mere estimates. The late Carl Sagan put the number of alien civilizations at 1 million, while science fiction writer Isaac Asimov put it at 670,000. Drake himself has the most conservative estimate at 10,000.
"These people may know what they're talking about," Shostak said. "If so, then we need to listen in the direction of a million or so star systems to have a good chance of finding ET. And that's something we could do in the next two dozen years."
With new technology SETI hopes to listen for signs of life in millions of star systems in earth's galaxy over the next 25 years. If the search for alien civilizations is like finding a needle in a haystack, "we know how big our haystack is " — there are several hundred billion star systems in our galaxy, Shostak said. So far, SETI has listened to only a small portion of that haystack — 750 star systems.
"SETI has been an enterprise for half a century now and we haven't found a signal" from intelligent life elsewhere in the universe, Shostak said. "Some people think that's significant but I don't think it is significant because we haven't looked at that many star systems."
SETI is listening for radio signals in the galaxy with a new array of 42 radio telescopes near Redding, but hopes to quicken the search for ET by expanding the array to 350 telescopes by raising another $35 million.
Shostak also bases his 25-year estimate on Moore's law, the well-known observation in Silicon Valley that a computer chip of the same size will double in power every two years. Computing power is a limiting factor in how quickly signs of alien life can be found via radio signals in the galaxy, Shostak said.
Deciphering a radio message from aliens may be another problem in itself, but simply having evidence that we are not alone would be world-changing, Shostak says.
SETI Institute, a 25-year-old group of over 100 privately funded Mountain View scientists, held its first ever convention on Aug. 13-15 at the Santa Clara Hyatt. SETIcon was attended by over 1,000 people, Shostak said.