Not too hot Not too cold Why is the Universe just right for human life?

Alastair McKay talks to Astrobiologist Paul Davies

TO explain the question he is posing, Paul Davies likes to talk about turtles. He has an anecdote which is attributed to both Bertrand Russell and the 19th century philosopher William James, concerning a lecture about the nature of the Universe. Halfway through the talk, a woman stands up and heckles the lecturer, saying that she knows how the universe is constructed. The Earth, she says, rests on the back of a giant elephant, which stands on the back of a giant turtle. The lecturer attempts to mock this suggestion by asking what the turtle is standing on. “You may be very clever,” the woman replies, “but you can’t fool me. It’s turtles all the way down.” It is obviously absurd to claim that the Earth is held up by an elephant on top of a stack of turtles, but the conventional explanations are no less problematic. At a certain point, the question departs the realm of strict logic, and becomes one of faith. The thing that supports this stack of turtles – what Davies calls a superturtle – can be God or science, but every explanation hits trouble when it reaches the vanishing point. If a beginning to the Universe can be established, what was there before, and what caused that beginning? These are not easy questions, even to an eminent physicist such as Davies, who did a great deal to popularise the subject in his 1992 book, The Mind Of God. That book took its cues from the concluding sentence of Stephen Hawking’s A Brief History Of Time, which suggested that the discovery of a complete theory of everything would be the ultimate triumph of human reason, “for then we would truly know the mind of God”.

Davies is an accomplished media performer – a regular on BBC radio – and worked at the universities of Cambridge, London, Newcastle and Adelaide, before taking up his current position at Arizona State. His interest in physics and cosmology has expanded into astrobiology, which attempts to explain the Earth’s origins, and takes him into that curious no-man’s land between Darwin and Jesus, where the word “God” is employed to symbolise everything from a bearded benefactor to the symmetry of an exploding void.

Davies knows this territory well, and is a concise, quick communicator, though it is a surprise to realise that even theoretical physicians have thoughts they would rather keep off the record. (His thoughts on the recent row about string theory must remain private.) He is aware, too, that even when employing the sci-fi metaphors of popular science, much of what he says will be incomprehensible. Once the tape machine is packed away, he tells me that many people know less than they think they do. “Ask them to explain what an atom is, and they’ll dry up pretty quickly.”

The Mind Of God was an accessible book, but Davies’s latest work, The Goldilocks Enigma, is chewier. Goldilocks is invoked as the book explores the question of why the Universe – like Baby Bear’s porridge – is “just right for life”. So the truth about existence is somewhere between a fairytale and a fruit machine.

Well, sort of. Forty years ago, Davies says, the Big Bang was one of many theories about how the Universe began. In the mid-1960s, physicists discovered heat radiation which confirmed the idea that the origin of the Universe was hot and explosive. During the 1980s and 1990s, satellites began to map out this radiation, which allows scientists to be confident about the physics until a trillionth of a second after the Big Bang.

“The Universe now is very complicated. But as you go back it gets simpler . That snapshot shows how extraordinarily simple it was. We know when the Universe began, how fast it’s expanding and something about what it’s made of.” But Davies does not stop there.

“It’s always hard for ‘why?’ questions to be tackled by scientists. They tend to work on mechanisms: how. Physicists like to think the laws of physics are the ultimate laws of nature. It’s the bedrock of reality. I just keep asking: well, where do they come from? And why have they got the form that they do, as it’s easy to imagine a different set of laws. Why? Who got to choose?”

The book does a thorough job of itemising the various theories of the Universe before the Big Bang. The default theory is that there is one Universe, which was started by a Big Bang. As this moment was the beginning of time, there was no before. “St Augustine in the fifth century proposed that the world was made with time and not in time. Einstein showed us 100 years ago that time was part of the physical universe – it’s not a separate thing. So if we’re talking about the origin of the Universe, it has to be the origin of space, time, and matter.”

If the Big Bang was the origin of the Universe, then the question of what happened before becomes a theoretical cul de sac. Davies cites Stephen Hawking’s comparison with the question: “What lies north of the North Pole?”

“If you had lived 1000 years ago and didn’t know about the spherical earth and cartography, you could sit at a dinner party berating a mariner, saying, ‘Why don’t you have an answer to the question?’ And the mariner would say, ‘Nothing lies north of the North Pole.’ The detractor would say, ‘You say there’s a land of nothing? What’s in this land of nothing? Is it hot, is it cold?’ The answer is there is no such place as north of the North Pole. It’s a mathematical absurdity. Same thing with the origin of time and the Big Bang. There isn’t a state of nothing there, there is no such place. No such time.”

That is the simple model, and Davies agreed with it until recently. Lately, he has been tempted by the idea that there wasn’t a single Big Bang. “There are bangs going on throughout space throughout time, and there’s this vast ensemble, a multiverse of universes.

“Either the Big Bang was a supernatural or a natural event. If you’re a scientist, you don’t want to believe in supernatural events. If it’s natural, there’s a physical process that can bring it about, and so if it can bring it about once, it can bring it about any number of times.”

The capsule version of Davies’s favoured theory is that the Universe both explains and fine-tunes itself. “There’s a sort of feedback loop between sentient beings and the laws that have given rise to them.” Further explanation of this requires a good deal of hand-waving. “But I have tried to go a bit beyond making those obvious statements and describe a mechanism by which this could take place.”

Theologians and physicists have a shared legacy, he says, of looking outside the Universe for answers. Theologians favour God, while scientists rely on the laws of physics.

“That’s always been a mystery. Why is the world mathematical? Stephen Hawking asks, ‘What is it that breathes fire into one set of equations and makes the Universe we describe?’ I’ve tried to suggest a new way of looking at the laws of physics as not being some pre-existing transcendent forms or relationships, but being inherent in the Universe itself, like a program being run on the great cosmic computer. So the Universe and its laws are somehow co-explanatory and co-emergent.”

At which point one may begin to sympathise with Andrew Marr, who (paraphrasing slightly) concluded Davies’s visit to Radio 4’s Start The Week with the observation: “My head hurts.”

It is tough stuff, but Davies is capable of playful inquiry. He indulges, and does not entirely reject, the notion we are creatures living in a matrix designed by superior beings, and is receptive to my suggestion that one of the problems of understanding this field is the inadequacy of the language.

“I wonder if we’re simply baffled because our minds have been built by evolution, just like our bodies. There are certain ways that we have to think about the world, like cause and effect, ‘what is a rational argument?’, and things like space and time, and all of these are part of what we’ve inherited from surviving in the jungle. As we go along asking questions framed in this way, we may never get the ultimate answers.

“That doesn’t mean there are no answers, but it may mean we need to await the arrival of machine intelligence. It could really be like Douglas Adams’s The Hitchhiker’s Guide To The Galaxy, where the great machine would come up with the answer .”

Some parts of Davies’s thinking seem to exist as a kind of riddle – a high-concept version of the conundrum about chickens and eggs. On the God question, he says that theologians must go beyond proving that God exists – they must also prove that he is unique: “Otherwise there could be a multiplicity of gods. If you’ve got all possible gods, you’ve got to choose this god.

“You’re right back to the same problem. And that has a neutering effect. Because if God is necessarily as God is, then God will necessarily make the Universe as it is, so why do we need the God anyway, because it was a necessity? And if it’s not a necessity, then it could have been otherwise, so that’s not an explanation. That makes the Universe seem like a whim.”

Confused? You should be. These are questions which no-one has yet managed to answer without invoking faith. The faith can be in God or in the laws of physics. Davies’s contribution is to suggest a mechanism by which these laws could have adapted. This includes the suggestion that what happens in the later stages of the Universe could influence how it came to exist. This may sound like science fiction, he concedes, but it doesn’t break the rules.

Davies has been involved in this argument for most of his career. One of his early works (“a very bad book”), God And The New Physics, was a speculative mix of cosmology and theology.

“Very little was understood about these things and I wanted to come up with some way of matching the science to the theology. But immediately you hit this argument: one person will say scientists will never give a complete explanation, we have to have a God, and the other person will say, ‘Why do we need a God, because who made the God?’ You get into this sterile debate which is being recycled .

“One person says it’s much easier for me to believe there’s an intelligent God who has made the Universe, than to believe that it’s just magically there, with all the properties it’s got, and Richard Dawkins will say it’s much easier to believe that the Universe exists and evolves its complexity than that a being as complex as an almighty God is already there. Well, you’ll argue forever. You can’t prove or disprove the other person’s position – you’re just arguing over whose superturtle is easier to accept on faith.

“There’s got to be a third way where we escape from having to depend on a superturtle; it’s only your cultural prejudice that would leave you to believe a designer superbeing is better or worse than a magical set of laws that just happens to exist.”

I tell him I like the notion of superturtles.

“Well,” he says, “some people are prepared to die for their superturtle. That’s the depressing thing.”

The Goldlilocks Enigma (Allen Lane,  £22) is out now

22 October 2006