Is Earth just an alien's lab?

Professional philosophers have shown little interest in space exploration." This comment appears on the first page of David Lamb's book, and is true enough, probably because very few professional philosophers have much knowledge of space research. But Lamb is an exception, and in producing a detailed study of the possibility of intelligent extraterrestrial life he has carried out a great deal of careful and painstaking research.

His approach differs from most other books on this absorbing subject, and he discusses all aspects of the question of life and intelligence beyond Earth. Beginning with a historical review, he continues with the scientific status of Seti - the Search for Extraterrestrial Intelligence - and then deals with a variety of associated topics, ranging from the detection of extra-solar planets to terraforming worlds such as Mars and Venus, flying-saucer reports and claims that Earth has been visited by aliens. He ends with a summary of the real chances that other intelligent races exist and, if so, how we could set about communicating with them if we were able to locate them.

He pays attention to some questions that are frequently glossed over, such as why should extraterrestrials want to make contact with us even if they knew of our existence - and what would be the benefits to us? Space scientists and philosophers may have rather different views, and Lamb is careful to give a wide range of opinions. He stresses that from the outset "Seti scientists have sought to distance themselves from Ufology and other branches of inquiry deemed to be pseudo-scientific", but he does give considerable space to some ideas that are not widely accepted by the scientific community. He is sympathetic to the ideas of Fred Hoyle and Chandra Wickramasinghe, according to which life on Earth was brought here by comets, and concludes that the theory "continues to gain in plausibility". He also describes Francis Crick's idea of "directed panspermia" - that life on Earth was deliberately seeded by highly advanced beings far away in the Galaxy. In general, philosophers are less likely than space scientists to be sceptical of ideas of this kind.

There is also the problem of what the author calls "the Great Silence"; why have we so far failed to pick up any messages from extraterrestrials? It may be because we are genuinely alone, or it may be because other intelligent beings are too far away; it may even be that the Intergalactic Council has "designated Earth as a nature reserve". The so-called peer hypothesis, due to Paul Birch in 1990, goes even further: we live in a universe created by super-intelligent beings. Again, philosophers may be more receptive than astronomers, and perhaps the author does not always make sufficient distinction between the possible and the wildly improbable.

Various methods of interstellar travel are discussed, mainly from a philosophical viewpoint. Certainly we are not yet ready to travel beyond the solar system. Whether "space arks" are practicable is very dubious, and all ideas of teleportation are no more than science fiction at present.

There are a few minor astronomical slips, but it would have been useful to point out that humanity cannot hope to migrate to Titan, Saturn's large satellite, when the Sun becomes a red giant star and increases in luminosity. Titan has a dense, nitrogen-rich atmosphere, but if the temperature were raised by only a few degrees, it would all escape. And the atmosphere of Io, Jupiter's volcanic satellite, is excessively tenuous; the density corresponds to what would normally be called an excellent laboratory vacuum. Life on Io is improbable to the highest degree.

But these are mere quibbles, and there can be no doubt that Lamb has written a valuable and important book. In some ways it breaks new ground, and it will appeal equally to astronomers and to philosophers. It is also written in a style that makes it accessible to readers with no previous knowledge of the subject. Few will quarrel with the sentiments in the last paragraph: "If extraterrestrial intelligence is found and contact is made, it will be truly important. If we do make contact our children will be astonished to discover that we made so little effort to do so, and then they will laugh at those who denied any possibility of contact. But if, after a massive search, we fail, that too will be important, as it will convince many of us that if this is all there is, we should do our best to protect it."

Sir Patrick Moore is an astronomer and the author of more than 60 books.