This week marked the 50th anniversary of one of the most ambitious, far-fetched and (at least so far) spectacularly unsuccessful undertakings in the history of science: the Search for Extraterrestrial Intelligence, or SETI project.

And one of its leading lights is now arguing that after five decades of intent listening for radio signals from outer space –- and being rewarded by nothing but fitful static from the rest of the universe – it's time for a different approach.

Dr. Paul Davies, a world-renowned cosmologist and astrobiologist at Arizona State University, has marked the project's 50th birthday by writing "The Eerie Silence: Why Do Aliens Ignore Us?" -- a brief history of a topic that has been touched on by hundreds of science fiction stories, movies or television shows.

"It was regarded as a quixotic enterprise at best in the early days. Back in the ‘60s one might as well have been saying you believe in fairies as work on SETI," Davies said in an interview with "It was seen as a crazy thing to do."

"Now the pendulum has swung the other way, so today I would say it receives widespread support. I might even say that the pendulum has gone a little bit too far: there's rather too much credulity in the scientific community for the possible existence of intelligent life. I think we have no evidence one way or the other. We should remain open-minded but skeptical."

"The Eerie Silence" is far more than just a history of SETI: it covers almost every topic related to the 50-year hunt for intelligent aliens, from an overview of its tentative beginnings at a West Virginia observatory to the philosophical underpinnings of the search for life, any life, beyond the confines of the Earth's atmosphere.

He pays tribute to pioneer SETI researcher Frank Drake, the astronomer who set up the first modern search for alien intelligence in 1960, calling it Project Ozma, after a character in the Wizard of Oz.

"There's not many people who would design an experiment, get null results for 50 years and still keep cheerful about it," he said. "It's astonishing."

But he argues in the book that after such a long silence, it's time for us earthlings to rethink the search for extraterrestrials entirely.

"It's a call to arms across the whole of the scientific community, saying ‘Let's not leave this to a small heroic band of radio astronomers,'" he said. "We need everybody to exercise our imaginations as to how alien technology might betray itself, what sort of footprint might it make … We shouldn't be fixated on radios."

Davies says we should all stop expecting distant alien civilizations to be beaming radio messages to us, or to be broadcasting so loudly in transmissions among themselves that we will be able to pick them up over the vast distances of interstellar space.

"I think that doing traditional SETI is very unlikely to succeed," he said. "We need to look at doing more things than just listening on the radio."

For instance, he suggests the existing banks of radio telescopes now dedicated to search for signals from outer space be allowed to search for radio beacons, automated radio broadcast stations set up by alien civilizations, which could keep beaming out a message long after those civilizations vanish.

"We could look for those, but I think that the problem with the way SETI is set up, both the hardware and the software, is that it's not directed at looking for a beacon."

Davies also raises the intriguing possibility that ET has already been here, millions of years ago, and left some trace of their presence, although he's quick to point out that he's a firm disbeliever in UFOs and alien abductions.

He suggests SETI expand to include searches for unusual geological, physical or even genetic evidence of alien presence, whether on Earth, elsewhere in the solar system or beyond. "We need to be mindful of anything that stands out; any anomaly; anything that doesn't look like it could have a natural explanation," Davies said.

"In other words, instead of looking for messages we look for signatures of technology, and we should look at anything that is weird, out of place, or not right; wherever it is, we should use the whole panoply of science, everything from nanotechnology and molecular biology right across to radio astronomy to find out what it is."

Despite the long silence, Davies believes the search is worthwhile. "Even if it doesn't lead anywhere, I think it's really important that we think deeply about such things as what is life, what is intelligence, what is the fate of mankind? Looking for intelligent civilizations out there is really in a sense looking for our own future," he said. "If the eerie silence out there is because all the other intelligent, advanced life forms have all blown themselves up then that's the fate that lies in store for us. These are deep questions which need addressing."

And besides, he continued: "It's a great way of getting young people involved in science. When you take surveys, there are two things [in science] that young people love. One is dinosaurs and the other is SETI."

Asked whether the search for intelligent life in space will ever succeed, Davies hesitates.

"It's certainly possible to argue that life is a freak accident that is confined to Earth and this is it. But I find that hard to swallow," he said. "As a human being I would just love to think that there are lots of aliens out there … but in terms of what are the chances it's very hard to put a number on it."

The Eerie Silence is published in Canada by Thomas Allen Publishers.