By Roger HighfieldThe chances are there's life out there, but any messages could be thousands of years old and indecipherable.
Aliens are probably common. Because there are billions of trillions of stars in the cosmos, many astronomers think it would be highly improbable for Earth to be the only rock to harbour life.
Whether ET is intelligent is still hotly debated. But no one doubts that the receipt of a signal from another civilisation would be Earth-shattering. "It would surely be the greatest discovery of all time, eclipsing the findings of Newton, Dawin and Einstein combined," says Prof Paul Davies, a British cosmologist from the Australian Centre for Astrobiology at Macquarie University.
"The knowledge that we are not alone would affect people's psyche, and totally transform our world view," he said during a visit to Britain last week. "The mere fact alone would be disruptive. But imagine if we got some serious information from ET. Then all bets are off about what our future would be."
Prof Davies is among the handful of scientists charged with thinking through the implications of what to do in the event of "first contact" with an alien, sitting on one of a clutch of committees led by Dr Seth Shostak of the Seti (Search for Extraterrestrial Intelligence) Institute in California.
The hunt for ET's transmissions has proceeded in fits and starts since 1959, when Cornell University physicists suggested that extraterrestrial civilisations would find it easier to reach out across the galaxy with radio waves than pay a visit. Today, perhaps the best known is being conducted by the Arecibo radio telescope in Puerto Rico.
Millions of people have signed up for the Seti@home programme, downloading a screen saver that analyses Arecibo data for the University of California at Berkeley.
And a major new alien hunt facility is under construction: the Allen Telescope Array at the Hat Creek Observatory some 290 miles northeast of San Francisco. The first 42 of a huge array of 350 small radio dishes are about to go into operation next month, opening a new ear on the cosmos.
Prof Davies has now become the chairman of the International Academy of Aeronautics' Post-detection Committee, which includes his colleague Carol Oliver and the Astronomer Royal, Sir Martin Rees. "Cynics say it is the best committee to be on because you don't have to do anything unless ET calls," said Prof Davies. "That is not entirely true because I intend to spruce up the protocol and have a few fire drills."
Some years ago, international astronomical societies agreed on what they call a "Declaration of principles concerning activities following the detection of extraterrestrial intelligence", The first step, it says, is to "verify that the most plausible explanation for the evidence is the existence of extraterrestrial intelligence rather than some other natural phenomenon or anthropogenic phenomenon".
Unlike the events shown in the film Contact (in which Jodie Foster portrays the celebrated Seti researcher Dr Jill Tarter), "there will be no Eureka moment," according to Dr Shostak. Instead, there will follow a painstaking process of checking and verification to discern a hello from the crackle of cosmic radio waves.
There have been many false alarms. In 1977, the "Wow signal" was picked up by researchers at Ohio State University, and so named after a professor scribbled the exclamation next to a printout of the signal. No one has heard it since.
Another set of rapid pulsing signals caused great excitement, until they were shown to come from a hitherto unrecognised class of super-dense rotating neutron stars now known as pulsars. Other emanations have been traced to automatic garage doors, satellites and a host of other gadgets. And, of course, there are hoaxes.
Prof Davies points out that, if a signal is shown to be authentically alien, it is most likely from a civilisation that is stupendously advanced compared with our own: by the time we receive it, it is highly likely that the transmitting civilisation will be millions of years in advance of us - if it still survives, of course.
To date, unfortunately "there has been nothing to set the pulse racing". But if he does suffer palpitations, the protocol says that the team that discovered the signal should telegram the International Astronomical Union and the secretary-general of the UN (as well as their own government). The International Telecommunications Union in Switzerland should also be alerted; it has the power to stop transmissions and would be asked to clear the frequency band that the aliens were using.
The discoverer, the protocol says, should make the announcement "promptly, openly and widely through scientific channels and public media". Dr Shostak emphasises there will be no "X-Files-style cover-up", or pressure from authorities to classify the discovery. But, of course, there will be endless hand wringing over how to manage the announcement and what to do about leaks to the media.
Then comes the question of whether to reply to ET. In April 1989, the trustees of the International Academy of Astronautics approved a protocol that declared finally: "No response to a signal or other evidence of extraterrestrial intelligence should be sent until appropriate international consultations have taken place.''
One problem is that it is doubtful a response can be drafted in advance. The nature and wording would depend on the possible meaning of the incoming message. "It could be an e-mail between stars that was never intended for us," said Prof Davies. Indeed, there is much debate about whether an alien culture with different histories and physical forms will have the same description of reality at all.
Perhaps ET could invent radio technology without ever developing the concept of an atom. But it does seem likely she would use mathematics to advertise her intelligence, given that it is a universal language. This much was recognised long ago. In the early 19th century, the mathematician Karl Friedrich Gauss suggested etching giant geometric figures in the snow of Siberia as a way of attracting the attention of Martians.
There is, of course, a chance, that an incoming message may be sent in response to messages extraterrestrials have already received from Earth. Some of our radio and television from the Thirties and Forties is just now reaching some of the nearer stars. What would aliens make of news of Neville Chamberlain's return from his Munich meeting with Adolf Hitler?
The problem is, however, that these signals have only travelled around 80 light years, too little for even the most optimistic Seti sage to raise the chance of meeting up with another civilisation. We may have to wait millennia for a reply, and Prof Davies speculates that it would probably come from an "information processor" that will blur the distinctions we make today between living organisms and artificial non-living machines.
But we should not limit our horizons to radio transmissions alone. Nasa has already shown the way in this respect: elaborate messages have been put on spacecraft such as the Voyagers now leaving the solar system, including a record with Earthly sights and sounds, such as music from Bach to Chuck Berry.
A laser beam could also be used to send a message. Indeed, our cells may carry one, too, Prof Davies speculates. DNA is mostly "junk", but what if it contains a message from an ancient alien civilisation? "We must not close our minds to communication by quite different means," he said.
Seti is "a glorious but almost certainly hopeless quest", he admits. But that does not mean it is a waste of time: Seti has many important spin-offs, not least those that will come from forcing scientists to grapple with huge issues of what counts as life and consciousness and whether the organisation of the universe fosters the evolution of living things.
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