The Goldilocks Enigma by Paul Davies

The prevailing view among scientists, says Paul Davies, is that life and consciousness are interesting bonus features of our universe, not essential components. Davies, however, thinks otherwise. His provocative and fascinating book argues that intelligent life is the reason why our universe exists.

Davies is a distinguished theoretical physicist and an acclaimed populariser of the subject, and this is not the first time he has strayed into territory more usually associated with theologians and philosophers. His previous books include The Mind of God (taking its title from Stephen Hawking's now notorious assertion that a complete theory of physics would unlock the Creator's intentions), and Davies won the Templeton Prize for progress in religion, worth more than half a million pounds.

It may come as a surprise, then, to find that the position he takes in The Goldilocks Enigma is one of complete agnosticism. Davies poses a great mystery - the fact that our universe appears tailor-made for life - and offers a number of possible solutions, including God, only to knock them down one by one.

To understand the enigma of the title, think of the way that stars burn. Stars are made of hot gas held together by gravity, and if the force of gravity were stronger than it is, stars would burn far more quickly and expire sooner. Our own Sun would have had a lifetime of only a few million years instead of the five billion it has already enjoyed, and life on our planet could never have had time to evolve. Equally, if gravity were weaker, then stars would burn too dimly, and their energy output would not support life. It seems that the strength of gravity, like Baby Bear's porridge, is "just right".

This kind of reasoning is known as the "anthropic principle", and gets a standard response from most scientists. The universe appears right for us, they say, because if it were otherwise then we would not be here to ask about it. Nature's rules are as random as a lottery ticket, and we happen to be lucky beneficiaries of the payout.

The snag, as Davies points out, is that while the lottery gets played every week, the universe began only once, so we are left wondering why nature chose the particular rules it did. Furthermore, the rightness extends to more than gravity; the tiniest changes in the laws of elementary particles would, he claims, make life as we know it impossible.

One answer could be that there are really lots of universes - a "multiverse" embracing every possibility - and Davies devotes the first half of his book to explaining how the multiverse theory has won support among cosmologists in recent years, thanks to developments such as cosmic inflation and dark energy. As with all Davies's books, the explanations here are clear and succinct; and in contrast with much popular physics writing of the last 20 years, there is a welcome tone of humility, perhaps because Davies has spent so much time conversing with people from disciplines outside his own. Though Davies clearly does not favour religious or mystical revelation over scientific deduction, he finds room to praise the insights of St Augustine, Leibniz and others, who approached the problem from a theistic perspective.

Since he is a physicist rather than a historian of ideas, one cannot expect Davies to go much further in acknowledging how modern physics was pre-empted by thinkers such as these, but the multiverse theory he describes closely resembles the so-called "principle of plenitude" - the idea that all things possible must be actual - which Arthur Lovejoy famously traced back to Neoplatonism in his classic study The Great Chain of Being.

So are we living in a multiverse? Davies remains "cautious". In a universe where everything is possible, it becomes possible that we are living in a virtual-reality fake, and since these fake universes take up little room there must be more of them than real ones, making us statistically likely to be prisoners of a Matrix-style con trick.

Leibniz had that one covered already: a beneficent God could never do anything so mean. Davies cannot resort to so comforting a notion; his colleague and fellow Templeton winner John Barrow has even impishly suggested that the architects of our fake world might give us hints of its falseness by tinkering with its laws as time goes on. Max Tegmark, another multiverse enthusiast whom Davies quotes, says our universe is real enough, but he offers an estimate in metres of the distance to the identical universe where another you is right now reading another version of this newspaper.

Davies is faced with a dilemma. He cannot believe in an intelligent designer, because of the classic "who made God?" argument. Equally, he cannot accept that our cosmos just happened to turn out right, nor that it is a dot in a multiverse of possible phonies. Davies's solution is a somewhat dramatic appeal to the more speculative corners of quantum field theory, general relativity and information theory.

Causality, he argues, could work backwards, so that the real cause of our universe is its endpoint. The point our cosmos is evolving towards could be one in which the whole of it becomes conscious. Philosophically minded readers might be reminded here of Spinoza, Kant, Schelling or Goethe, all of whom said strikingly similar things. Davies, it seems, is a new Romantic - if not a postmodernist.

This is a hugely enjoyable book, and in its first half a highly informative one, but sceptical readers will question its initial premise: the so-called enigma. People used to apply the Goldilocks argument to Earth's orbit, saying it was just the right distance from the Sun - but then it became apparent that far-off worlds such as Jupiter's moons might harbour life of an entirely different kind. Unless we can discover other beings elsewhere in our galaxy, all argument about whether life is an essential or superfluous part of the cosmos is pure speculation. Our conclusions, as Davies himself admits, are a matter of personal faith.