Finding life on other planets (Aliens!) is a tantalising prospect that occupies our daydreams. And yet with the constant onslaught of new technology are we fast approaching a time when it could become a reality?

By Bruce Dorminey

To humans, the idea of being alone in a Universe at least 10 to 13 billion light years across is disconcerting. The philosophical ramifications of being alone in such an overwhelming expanse of spacetime cannot be overstated. Given everything we know about the current rate of star and planetary formation, however, it would seem illogical that we should be the only sentient beings in the Universe. And given what we do know about the structure of life here on Earth and of molecules found thus far in the interstellar medium, it would appear that carbon could be the key to life's development anywhere in the Universe.

While we can only continue to speculate about the extraterrestrial development of life and intelligence, we do know that carbon production is based on the rate of star formation. Estimates by the Hubble Space Telescope strongly suggest that carbon production peaked almost 7 billion years ago. Given the time span necessary for biological evolution as we know it, some theorists now believe that it is highly unlikely that the Universe could have seen the first carbon-based intelligent life any sooner than 3 billion years ago, or when the Universe was already more than 10 billion years old. In other words, the evolution of extraterrestrial intelligent life could be a very "recent" cosmic phenomenon. In fact, as Mario Livio from the Space Telescope Science Institute and Charles Lineweaver from the University of New South Wales in Sydney have both pointed out, the Universe may only just be awakening to an epoch of intelligent life. As Lineweaver has noted, at this stage in our own development, it is impossible to know whether we have come late or early to the cosmic party, but in the long history of our Universe, we might be relative newcomers.

What kind of transport and communications can we expect ET to have?

If there are extraterrestrial civilizations capable of communicating as we do, shouldn't it follow that the same basic physics also held for their evolution? Life as we know it, has its best chance of developing on an Earth-like, fast-rotating planet in orbit around a Sun-like star, which has a hydrogen-burning phase that would provide a stable environment for life to evolve. And even with those parameters in place, ETs would likely emerge only after their home world had developed some sort of genetic code. They would also have to become cognizant enough to communicate with each other. Yet in order to communicate over interstellar distances, extraterrestrials would first have to overcome the gravity of their own planet. In order to communicate with us, as Seth Shostak of the SETI Institute frequently points out, they would have to develop the dexterity to build technology and telescopes.

If they chose radio, they could easily overcome the universal cacophony of background noise in the electromagnetic microwave region (1,000 to 100,000 megahertz). Just above the terrestrial TV and FM bands, it is relatively quiet. There, only a trace of background radiation from the Big Bang remains. (This is an effect anyone can hear in the form of soft constant static when flipping the dials on an FM radio.) However, the pursuit of ET in the radio spectrum has a short history. Although decades, even centuries earlier, there were many ideas about how to signal or find extraterrestrial civilizations, the genesis of modern SETI really began only some 40 years ago.

In a paper published in Nature in 1959, the Cornell University physicists Giuseppe Cocconi and Philip Morrison suggested that the most effective way of communicating across galactic distances had to be via radio waves. At about the same time, Frank Drake, a young radio astronomer at the National Radio Astronomy Observatory in Green Bank, West Virginia, was working on a pet project named Ozma. (The name came from the mythical Princess Ozma, featured in L. Frank Baum's fabled Land of Oz: a place far, far away, populated with strange and exotic beings.)

NRAO and Associated Universities Inc. The 26 metre (85 foot) Tatel Radio Telescope which was built in 1958.

Drake became the first radio astronomer to attempt to detect interstellar radio transmissions from an extraterrestrial intelligence. On April 8, 1960, he used the novel combination of sensitive new receivers and a 26-metre radio telescope to survey several nearby stars, the first of which was Tau Ceti, an early-morning star in the Cetus constellation some 3.3 parsecs (a parsec being a distance of approximately 3.26 light years) from Earth. Drake picked up a strong signal almost as soon as he began scanning with his single, 100-hertz receiver at the 21-centimetre emission line (1,420 megahertz), which is the emission frequency of cold hydrogen from interstellar space. Yet some weeks later, Drake learned that the "signal" was really terrestrial interference from a secret U.S. military project.

Despite this frustrating experience with radio frequency interference (RFI), Drake's efforts prompted a request from the National Academy of Sciences asking that he organize a 1961 meeting to discuss the budding Search for Extraterrestrial Intelligence, or SETI and shortly thereafter the institute was founded.

As University of Arizona astronomer Neville Woolf points out, looking for evidence of ETI in the radio spectrum could well be futile, because the ETI may have long moved on to more advanced forms of communication, which our own technologically primitive civilization has yet to realize. "Radio SETI is a noble search", says Woolf. "Yet, if we were to look for ETI technologies by looking for giant steam engines, people would laugh because they would say that's old technology. But what's old on the scale of a Universe that's 10 billion years old?

Ly Ly/SETI Institute An Artist's Conception of the Allen Telescope Array, due to go into full operation by 2005 in the California Sierra mountains northeast of San Francisco. With its eventual collection of more than 1,000 antenna, its SETI target list will ultimately number as many as a million stars.

In truth, no matter how dogged our efforts to find extraterrestrial intelligence, and how advanced the technologies, SETI astronomers may still miss the mark. "Back-of-the-envelope" calculations on the median age of possible extraterrestrial civilizations suggest their technologies would be several million years ahead of ours. Thus, trying to detect their communications or signals in the radio and optical spectrums may indeed be as futile as trying to log on to the Internet by banging on a "talking" drum. How can we second-guess an extraterrestrial civilization that could be millions of years ahead of us, if we cannot accurately envisage what Earth technology will bring in only several hundred years? We've moved from basic laptop computers to wireless Dick Tracy-style communicating watches in 10 years. What will be wrought in 10 million years? As Stuart Bowyer, a retired Berkeley radio astronomer and long-time SETI advocate, reminded me, we are simply stuck with the physics that we understand thus far. Bowyer believes that even if other civilizations are very advanced, communication in both the radio and optical spectrums will remain viable, and, therefore, should remain central to SETI's overall approach. He asserts that in the next 40 years, or by the time NASA and ESA have produced high-resolution images of an extra-solar "earth", SETI astronomers will have had a "fair chance" of finding extraterrestrial technology.

The Pioneer F spacecraft, destined to be the first man made object to escape from the solar system into interstellar space, carries this pictorial plaque. It is designed to show scientifically educated inhabitants of some other star system, who might intercept it millions of years from now, when Pioneer was launched, from where, and by what kind of beings. (With the hope that they would not invade Earth!)

But even if a signal, or "leakage", is detected, it would be doubtful that we could decipher it, unless it was intended as an all-points-directed beacon designed to be decipherable for any civilization that lay in its beam. Certainly, signal detection would confirm that we were not alone in the Universe, but true interstellar communication, even over short distances, would necessitate a transgenerational attitude of collective long-term effort. Signals sent and returned over distances as short as 10 parsecs would require a round-trip communication transit of at least 65 years, or basically a human lifetime. Sustaining such interest in the public at large may prove to be optimistic at best. Imagine a student in a third-grade class some time in the future: the teacher announces that SETI astronomers have just detected a signal containing a message from an intelligent technology-bearing extraterrestrial civilization on an Earth-like planet circling a nearby star. The announcement would initially be greeted with emotions ranging from excitement, consternation, curiosity, and bewilderment. Universities would likely offer whole new curricula based on how Earth's religions and philosophies would be affected by the news. The Nobel Committee would award prizes, and the media would have a field day. But by the time the message had been deciphered, and the international community had agreed upon and sent humanity's response, the student would hear the news of ET's reply as he was "getting the gold watch" at his retirement party. So, dreams of interstellar E-mail are slightly optimistic.

While profound certainly, the detection of an alien intelligence, even within 100 parsecs from Earth, would not be something that most people would think about on a day-to-day basis. Life would simply go on.

An Abridged extract from 'Distant Wanderers' by Bruce Dorminey (C) By permission of (Copernicus Books,$29.95/£22) An imprint of Springer-Verlag New York, Inc Available to buy from Amazon.co.uk and Amazon.com. Bruce Dorminey was a winner in the Royal Aeronautical Society's Aerospace 1998 Journalist of the Year Awards. He writes about astronomy and astrophysics for numerous publications. This is his first book.