Meeting extraterrestrials: Should we contact aliens?

As you read this, the metal dishes of 42 radio telescopes, hidden in a little-visited valley in California's Cascade Mountains, are locked on to a star system hundreds of light years away. Together they will scan 10 billion radio channels, searching for signals deliberately sent by intelligent aliens or accidentally leaked from their planets. Then the dishes will turn to the next star and its satellites.

The 42 devices of the Allen Telescope Array (ATA) have already taken a preliminary look at Kepler-452b, the potentially habitable, Earth-like planet whose discovery was announced last week. And "so far, any inhabitants of Kepler-452b are remaining coy," admits Seth Shostak, of the SETI [Search for Extraterrestrial Intelligence] Institute, which runs the telescope. But Dr Shostak, its director of research, is anything but disheartened.

"Right now," he says, "there could be radio waves zipping through your body that have come from another planet. But if there are no signals, it would mean that, of the trillion planets in our galaxy – roughly 10 per cent of which are amenable to life – Earth is the only place with critters that have understood science and built technology based on it. So, if this is the only place in the galaxy with intelligent life, then Earth is some sort of miracle – and we scientists tend to think that, if you say something is a miracle, you haven't studied statistics."

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It seems that hopes for discovering intelligent alien life have rarely been higher. In the same week of the Kepler-452b revelation, the billionaire Russian internet entrepreneur Yuri Milner announced he was funding Breakthough Listen, a new, decade-long $100 million (£64 million) project dedicated to the quest. And the money, one of the biggest ever donations to the search for alien intelligence, led Professor Frank Drake, Chairman Emeritus of the SETI Institute and adviser to Breakthrough Listen, to declare: "We will have the most powerful and enduring search that's ever been launched."

Which, of course, does not alter the fact that so far we have found nothing. But, explains Dr Shostak, finding alien life was never going to be straightforward: "If aliens had been looking at Earth with a radio telescope, they would have found nothing during the first four and a half billion years. Earth may have had microbes, or dinosaurs, but we only became detectable around the time of the Second World War, with the invention of radar."

Another potential problem is that, while we search using our technology, the extraterrestrials may have devised a far more sophisticated means. "Maybe," says Dr Shostak, "we are sitting around like 15th-century inhabitants of the New World, waiting for drum beats to prove the existence of Europeans."

It isn't just Hollywood film makers who have considered this. In 2010, Professor Stephen Hawking warned against actively seeking to make contact, saying: "We only have to look at ourselves to see how intelligent life might develop into something we wouldn't want to meet." But, says Dr Shostak, it is already too late to hide. The signals that have leaked from Earth are now 50-60 light years out. Every day, our TV signals wash over another star system. Which does at least mean, says Dr Shostak, that "it's too late to worry about it". Besides, if we do discover something out there, we might find our reactions are strangely … human.

"In the summer of 1997," admits Dr Shostak, "the ATA picked up signals seemingly sent by extraterrestrial life. It was actually a [human-made] satellite sending signals that mimicked what we would expect from aliens. But for 16 hours we thought we might have found intelligent extraterrestrial life. And yes, I was nervous – because I thought I was going to have to reshuffle my entire diary, and wouldn't be able to make the party that was coming up that Saturday night."