Imagine standing on the west coast of Ireland a thousand years ago, told to remain on guard against a potential invasion. Then imagine looking out across the ocean, not knowing if there are any lands out there to be invaded from. Even if there are any lands, there is no way of telling whether they’re inhabited. You could spend your lifetime watching out for invaders who couldn’t exist.
This is roughly the position Paul Davies finds himself in. He is the chair of the SETI (Search for Extra-Terrestrial Inteliigence) Post-Detection Taskgroup. If we do ever establish the existence of sentient aliens, it is the task of his organisation to try to form the interface between them and humanity. He lives his life preparing for an event that not only may never happen, but which may never be able to happen. There may be no intelligent aliens, anywhere, ever.
Davies’ book The Eerie Silence: Are We Alone in the Universe? is both an important and a timely publication. Its importance is simply justified. There are only two possibilities: either the Earth is the only planet in the universe to harbour sentient life, or it is not. Each of these possibilities is, as Arthur C. Clarke famously noted, so astonishing as to verge on the incredible.
There is a good reason why this should be a problem now in a way that it has never been in human history. Until very, very recently (just two hundred years!) it was entirely rational to believe that humans were the only sentient species because the universe was a) very small and b) very young. The only rational explanation for the existence of humanity in such a universe was to accept the existence of a creator, who made us. All religions tend to assist that belief.
Our new understanding that the universe is very, very big, and very, very old, makes both our possible outcomes intensely weird. The idea that life exists on a single planet amongst all the billions of galaxies in the universe is unimaginably unlikely, unless some truly inscrutable deity gave life to one planet only, and created the rest of the universe as some kind of strange doodle on a scale that renders the Earth microscopically insignificant. This itself poses a major question about our conception of such a deity.
The alternative is that life exists on other planets. Yet mankind, as a species, has never had cause to believe this, because it has had zero evidence. Some people, such as Swedenborg, have believed that the universe teems with life, but that is just a matter of faith. The scientific answer has, up until now, always been a zero. We are alone.
The difference between mere faith and knowledge based on evidence is absolute. Proof of the existence of extra-terrestrial life would entail a greater revision of all our scientific understanding than any other single discovery in human history, because we would have to re-write the entire story of life, its evolution and the nature and extent of its existence. ‘Give me one microbe’, Archimedes might say, ‘and I will move the world.’ The discovery of sentient life would add a further dimension, as we discover whether it is similar in nature to our own or radically different, more advanced than ourselves or less so. Theists and atheists alike would have to readjust the very basis of their understanding of what it means to be alive, and to be human.
True, if we are alone in the universe we shall probably never be sure of that, although scientific detection methods will soon be able to demonstrate the non-existence of life in observable space. However, if life does exist elsewhere we are likely to detect it very soon. An American astronomer, Steven Vogt, recently claimed that the likelihood of life existing on the newly discovered exoplanet Gliese 581g was ‘100%’. This means that the publication of The Eerie Silence is exceptionally timely, because it would be too late to discuss how we should react to the discovery of alien life after it has already happened.
In his book, Paul Davies offers a completely dispassionate assessment of the state of our knowledge, and the ways in which we might seek for extra-terrestrial intelligence. What is remarkable is the fact that Davies, despite his position, retains a completely open mind about the possibilities and carefully maintains the scientific detachment necessary to avoid drawing unwarranted conclusions. After arraying all the evidence, the closing statement of the book is ‘we just don’t know’ (page 208, his italics). This means that the reader has confidence in Davies’ impartiality as he goes over all the necessary ground in an eloquent but concise series of chapters: whether life is unique, rare or commonplace, whether alien intelligence could exist, and what form it might take.
He deals with the two most common formulations of SETI, Drake’s equation and Fermi’s paradox, but goes much further than this. He explores whether alternative forms of life might already exist on Earth ( the ‘shadow biosphere’), and he scrupulously analyses the problem of the ‘Great Filter’. This is a mathematical model that explores whether intelligent life is likely to have time to evolve during the time when a planet’s conditions are able to sustain life, the so-called ‘habitability window’. This section is typical of the book in that it involves mathematics and requires close reading, but the arguments are lucidly communicated and their validity carefully weighed.
Davies goes far beyond the popular idea of aliens as obviously recognisable. In an important chapter titled ‘New SETI: widening the search’ he examines the possibility that alien intelligence might exist in forms we cannot easily imagine, and may not even recognise. He accepts that alien intelligence may well have passed beyond the biological stage, which our own computer-driven and technological culture suggests may happen to our own species eventually. He discusses, among many other things, Matrioshka brains, von Neumann machines and quantum minds. You feel that Davies would not be uncomfortable with Douglas Adams’ planets inhabited by ‘super-intelligent shades of the colour blue’. The beauty of The Eerie Silence is therefore that it deals with where we are now, with our primitive search for radio-based emissions from alien cultures, and where we might be in the future, when radio waves are seen as a temporary stage in our technological advancement.
As well as the purely scientific aspects, Davies considers the impact of any discoveries we may make. He examines the effects on science, philosophy and politics, and in particular religion. He suggests that an alien message would ‘shake up the world’s faiths’ (p188), but that Christianity would face the biggest challenge, because ‘Jesus Christ was the saviour of Homo sapiens, specifically: one planet and one species’ (p188). If sentient alien species exist, then either God has provided separate incarnations for each one (Davies entertainingly reports an Anglican priest as expressing this as ‘God taking on little green flesh to save little green men’ (p189)), or Christ’s incarnation was to save all sentient species, in which case the Earth is their spiritual home. If on the other hand aliens have no need of salvation, then they are unfallen and analogous to angels. All of these interpretations are uncomfortable, at least, and show the relevance of discussing the implications of alien contact even before we know such contact is possible.
The Eerie Silence will be superseded, because our knowledge of the universe outside our solar system is developing at a considerable rate. Nevertheless, the issues it raises and the thoughts it provokes merit wide consideration and debate in these years when we are just beginning to find the planets on which alien life could exist. Even if we do not have much time to reflect on these matters as we go about our daily lives it is comforting to know that there are people like Paul Davies standing on guard against a day that may never come – but which we would all find immensely exciting if it did. If there are sails out there, whether they belong to traders or an invasion fleet, he will be one of the first to know.