The reality is that intelligent life is probably out there

AT THE Nuffield Radio Astronomy Laboratories at Jodrell Bank this week a major new collaborative research project has begun. Together with colleagues from the SETI Institute in Mountain View, California, astronomers are attempting to detect faint radio signals from intelligent life elsewhere in our Galaxy.

This research, called Project Phoenix, uses the University of Manchester's 76-metre Lovell radio telescope and the 305-metre US radio telescope based at Arecibo, in Puerto Rico. By using two telescopes it is possible to discriminate between signals of an extraterrestrial nature and those that are from within the Solar System. This will be the most sensitive and comprehensive search for extraterrestrial signals ever carried out.

Whether or not we are alone in the universe is a question that has vexed humankind for many centuries. But we are privileged to live in an era where the technology exists to make a serious attempt at its resolution. A belief in the existence of extraterrestrial life is often as personal as religious conviction and perhaps as much based on faith. But scientifically the possibility cannot be discounted and, perhaps more than any other time in history, the subject can rightly be regarded as a respectable discipline.

Before we even begin such a search we must address the question of whether there is some chance of success. For example, can we estimate the number of civilisations within our own Milky Way galaxy? This is a question that has been asked many times, but scientists now believe they now have a reasonable knowledge of the factors involved in producing such civilisations.

The rate of formation of suitable stars - that is, ones which are hot enough to sustain life and live long enough to allow life to evolve - is a crucial starting-point. Astronomers can easily assess this rate of formation at about one star per year. However, these stars also need to have habitable planets.

Only in the last five years has astronomical science found evidence that at least some stars (other than our own star, the Sun) have planetary systems. Current belief is that perhaps one in 10 stars have planets orbiting them. But we also require that these planets are warm enough to have liquid water, a basic component of life on Earth and presumably life elsewhere, and are large enough to retain an atmosphere that can both provide protection and sustenance to developing life.

Next we must assess the fraction of these suitable planets that actually develop life. Since life developed on Earth almost as soon as conditions were right, it is reasonable to suppose that life would form on any such suitable planet. But we cannot assume that these lifeforms will evolve into "intelligent" beings. It took 3,000 million years for intelligent beings to develop on Earth, which may mean the process is difficult and therefore uncommon. But it may be reasonable to assume that any intelligent lifeforms will then go on to develop the necessary technology with which to attempt interstellar communication.

The final critical question is how long such an advanced civilisation survives. Humankind has only been transmitting radio signals since the 1920s and if our civilisation were destroyed tomorrow, through our own negligence or some natural catastrophe, we would only have existed as an "intelligent civilisation" for a tiny fraction of the lifetime of the Earth.

It may be that other civilisations in the universe come and go in this way, sparking into existence for only a brief time. Then our chances of detecting these civilisations is very small. But if these civilisations can exist for millions of years, we have a good chance of finding at least some of them. Given optimistic guesses, where possible based on scientific and sociological evidence, most predictions imply there would be many thousands of such civilisations. Our searches will only be successful if some of these have a willingness to attempt to communicate with others.

The present attempt at detection is technically the most sophisticated and comprehensive search yet performed. The advanced radio receivers used at Jodrell Bank and Arecibo detect a broad band of radio frequencies. This band is split up into hundreds of millions of very narrow channels, each one only 1 Hz wide. Computers then search each channel simultaneously for patterns in frequency or time that indicate whether a continuous or pulsed signal is present. Any prominent candidate signals are then looked at more closely to determine their origin and nature.

We are looking for a signal that is obviously coming from beyond the Solar System and which cannot be due to any known natural process. Obviously, signals from other distant civilisations are likely to be very faint, so Project Phoenix concentrates on star systems relatively close by; within about 200 light years of Earth.

Those involved in this kind of research have no hidden agenda. Strict protocols for announcing discoveries to both the scientific community and the media are already in place. The detection of a signal from another civilisation would surely have a profound global impact. Studies to assess the public's likely reaction to such a discovery have concluded there would be confusion and excitement but little panic or hysteria.

But the world is unlikely to change radically overnight; rather, a slow realisation and yearning for more information is likely to follow. We will know very little about this extraterrestrial life. We have no way of knowing how such life may differ or be similar to us and we must consider the possibility that the civilisation might not be benign before we attempt communication.

We must bear in mind that any signals we send in reply will take many years, perhaps centuries, to reach their destination. This would be perhaps the most frustrating part of our greatest revelation

It is difficult to assess the chances of success for Project Phoenix. Since the experiment is targeting only nearby stars, we would be fortunate indeed to find them this time around. However, if we don't attempt such a search our chances of success are zero.

But failure, if it comes, will not necessarily mean we are alone, perhaps only that we have not yet looked hard enough. In that case we should look to the prospects of future generations attempting to answer this same question. Whatever one's personal beliefs, if we succeed, it will represent the greatest discovery we shall ever make.