alines are real......

In February 2008, Nasa sent the Beatles song, Across the Universe, across the universe. Pointing the telescopes in its Deep Space Network towards the north star, Polaris, astronomers played out their short cosmic DJ set, hoping that it might be heard by intelligent aliens during its 430-year journey to the star.

The hunt for intelligent species outside Earth may be a staple of literature and film – but it is happening in real life, too. Nasa probes are on the lookout for planets outside our solar system, and astronomers are carefully listening for any messages being beamed through space. How awe-inspiring it would be to get confirmation that we are not alone in the universe, to finally speak to an alien race. Wouldn't it?

Well no, according to the eminent physicist Stephen Hawking. "If aliens visit us, the outcome would be much as when Columbus landed in America, which didn't turn out well for the Native Americans," Hawking has said in a forthcoming documentary made for the Discovery Channel. He argues that, instead of trying to find and communicate with life in the cosmos, humans would be better off doing everything they can to avoid contact.

Hawking believes that, based on the sheer number of planets that scientists know must exist, we are not the only life-form in the universe. There are, after all, billions and billions of stars in our galaxy alone, with, it is reasonable to expect, an even greater number of planets orbiting them. And it is not unreasonable to expect some of that alien life to be intelligent, and capable of interstellar communication. So, when someone with Hawking's knowledge of the universe advises against contact, it's worth listening, isn't it?

Seth Shostak, a senior astronomer at the Seti Institute in California, the world's leading organisation searching for telltale alien signals, is not so sure. "This is an unwarranted fear," Shostak says. "If their interest in our planet is for something valuable that our planet has to offer, there's no particular reason to worry about them now. If they're interested in resources, they have ways of finding rocky planets that don't depend on whether we broadcast or not. They could have found us a billion years ago."

If we were really worried about shouting in the stellar jungle, Shostak says, the first thing to do would be to shut down the BBC, NBC, CBS and the radars at all airports. Those broadcasts have been streaming into space for years – the oldest is already more than 80 light years from Earth – so it is already too late to stop passing aliens watching every episode of Big Brother or What Katie and Peter Did Next.

The biggest and most active hunt for life outside Earth started in 1960, when Frank Drake pointed the Green Bank radio telescope in West Virginia towards the star Tau Ceti. He was looking for anomalous radio signals that could have been sent by intelligent life. Eventually, his idea turned into Seti (standing for Search for Extra Terrestrial Intelligence), which used the downtime on radar telescopes around the world to scour the sky for any signals. For 50 years, however, the sky has been silent.

There are lots of practical problems involved in hunting for aliens, of course, chief among them being distance. If our nearest neighbours were life-forms on the (fictional) forest moon of Endor, 1,000 light years away, it would take a millennium for us to receive any message they might send. If the Endorians were watching us, the light reaching them from Earth at this very moment would show them our planet as it was 1,000 years ago; in Europe that means lots of fighting between knights around castles and, in north America, small bands of natives living on the great plains. It is not a timescale that allows for quick banter – and, anyway, they might not be communicating in our direction.

The lack of a signal from ET has not, however, prevented astronomers and biologists (not to mention film-makers) coming up with a whole range of ideas about what aliens might be like. In the early days of Seti, astronomers focused on the search for planets like ours – the idea being that, since the only biology we know about is our own, we might as well assume aliens are going to be something like us. But there's no reason why that should be true. You don't even need to step off the Earth to find life that is radically different from our common experience of it.