The bear necessities of life...

The 'just rightness' of the universe for life puts Paul Davies in mind of baby bear's perfect breakfast in Goldilocks . He hopes his think-tank will transcend subject boundaries in its quest to discover why the cosmos seems rigged.

For thousands of years, human beings have gazed in awe at the world around them and asked the big questions. How did the universe come to exist? Why is it arranged the way it is? Is there any meaning to it all? Questions of this sort are standard fare for priests and philosophers, but have usually been considered off-limits for mainstream scientists.

Increasingly, however, physicists and cosmologists have been prepared to confront such sweeping foundational questions, but in so doing they have provoked a bitter backlash from many of their more hard-headed colleagues.

In the 20th century, science advanced so rapidly that most disciplines fragmented into very narrow specialisms. It is only necessary to glance at the obscure titles of many science journals to see how apt is the well-known dictum that scientists know more and more about less and less. But towards the end of the past century there was a growing feeling that physical science might be converging on a grand unity, maybe even a final theory in which all the basic features of the physical world could be captured by a single mathematical statement - the famous "formula on a T-shirt". A longstanding contender was string theory, which attributes all the fundamental forces and particles of nature to the antics of little stringy loops vibrating in various patterns. Although cynics shrugged aside string theory and other ambitious unification programmes as a touch of millennial madness, the lure of complete unification remains a compelling goal for theoretical physicists.

Cosmology has also contributed to the vision of grand unification. Dramatic progress in observations using satellites and telescopes has enabled astronomers to piece together the story of the universe in unprecedented detail, right back to the first split second after the big bang, and has served to focus attention on tough conceptual issues such as what happened before the big bang and whether something (for instance, the universe) can come from nothing.

One result of this thrust towards a deeper and more integrated understanding of the universe has been a radical reappraisal of the laws of nature. Science is predicated on the belief that the physical world is ordered according to universal mathematical rules. When I was a student in the 1960s, the laws of physics were presented to us as "given"; nobody seemed to ask the obvious questions of where these laws came from or why they have the form they do. But the drive to amalgamate and unify the laws has thrown the problem of their origin into sharp relief. Could these laws have been different and, if so, what exactly determined the laws that the universe actually possesses?

A clue comes from asking whether there is anything special or unexpected about the observed laws, as opposed to the seemingly limitless possible alternatives. And, as it happens, the answer is yes. It has long been known that the existence of life in the universe depends rather delicately on a number of felicitous coincidences and special factors in fundamental physics and cosmology. Like Baby Bear's porridge in the story of Goldilocks, the cosmos seems to be "just right" for life - an intriguing property expressed bluntly by the late cosmologist Fred Hoyle as "a put-up job".

One way to think about this is to imagine playing God, using a sort of designer machine to make a universe. Imagine twiddling a knob and making, say, the electron a bit heavier or gravity a bit stronger. According to the standard models of particle physics and cosmology, there are 30-odd parameters that are undetermined by existing theory, so we might imagine a similar number of knobs. Calculations then suggest that meddling with some of the knob settings, even by a tiny amount, would prove lethal, stymying any chances that life could emerge in the universe. The knob settings that characterise the real universe look suspiciously like a fix.

One way to explain the impression that the universe has been cunningly rigged in favour of life is to appeal to the multiverse theory. Many cosmologists believe that the (as yet unknown) physical process that generated the big bang created not one but a vast ensemble of universes, of which ours is merely a single representative. Furthermore, they think the laws of physics we find in textbooks are not universal and absolute but, rather, "effective", valid for good approximation under the relatively low energies encountered in the lab. In the ultra-hot conditions of the very early universe, however, the true underlying laws would have been manifested, albeit fleetingly. Then, when the universe cooled during the first split second, the familiar bylaws emerged. Theoretical modelling suggests that this transition could have had a random element, leading to different bylaws in different cosmic domains, or "universes".

Take a God's-eye view of the cosmos and it would resemble an elaborate patchwork of universes, each characterised by its own distinct bylaws, randomly assigned. Very rarely, Lady Luck would generate a patch with all the right parameters to permit life. It would then be no surprise that we find ourselves located in such a bio-friendly Goldilocks universe, because we obviously would not be around to observe one hostile to life.

The multiverse theory, neat though it may be, has provoked a fierce response. The holy grail of theoretical physics is the creation of a comprehensive final theory that would be complete in all respects. It would describe a unique universe in which the values of all the apparently arbitrary parameters, such as particle masses and force strengths, would be explained in terms of the theory. There could be no cosmic patchwork, because only one possible universe could exist in conformity with the theory. The fact that this unique universe conveniently happened to be bio-friendly must then be accepted as an unexpected bonus, a sheer fluke.

This may seem a stretch, but if life and consciousness are shrugged aside as being of no significance - a point of view that many scientists hold anyway - then the flukiness is a non-issue.

Proponents of a unique final theory slam the multiverse idea as untestable, describing it as dangerous quasi-religious pseudo-science. Multiverse enthusiasts have in turn accused the unification theorists of promissory triumphalism because nobody has yet demonstrated a credible unique theory, let alone predicted the values of any Goldilocks parameters.

This acrimonious wrangling reveals deep divisions concerning the ultimate goal of science, the nature of physical reality and the place of conscious observers in the grand scheme of things. It raises far-reaching and unresolved problems, such as what is life and what is the universe? Over the past couple of decades, physicists, cosmologists, biologists and other scientists have discussed these foundational questions of science at a growing number of conferences and workshops, or expressed their opinions informally through websites such as www.edge.org or the Los Alamos electronic archive.

Earlier this year, I was invited to create a special research institute at Arizona State University dedicated to probing the conceptual foundations of science - a sort of cosmic think-tank. The institute fits squarely with a series of initiatives by ASU president Michael Crow, designed to transcend traditional subject boundaries and foster interdisciplinary research by making it easier for experts in different fields to work together on topics at the edges of their disciplines. And the "Goldilocks enigma", which cuts across conventional subject boundaries, provides a classic example.

A major focus of the new institute will be the study of origins: the origin of the laws of nature, the universe, of life and of consciousness, for example. The institute will host a series of workshops and visitor programmes and involve the wider public through special lectures and outreach projects. Although specific research themes are likely to be highly specialised, the broader results of our deliberations should be of great interest to non-scientists, too.

The entire scientific enterprise hinges on the assumption that nature is intelligible to human beings. Most scientists accept this premise as an act of faith and simply get on with the job. But when reflecting on the ultimate questions of existence, we cannot avoid addressing the puzzle of why mathematics and the scientific method work so spectacularly well in helping us to understand the physical universe. How are we able to unravel nature's mysteries in this way? Why can the human mind, a product of evolution, glimpse the hidden rules according to which the universe runs? The confluence of physics, cosmology and biology may provide the key, holding out the hope that we may one day discern the true place of humankind in the great cosmic scheme.

Paul Davies is author of The Goldilocks Enigma: Why is the Universe Just Right for Life?, published by Allen Lane, £22. He has been appointed director of a new cosmic think-tank at Arizona State University.