The end of science? No, the beginning

It has become fashionable to speculate that science - specifically, physics, the king of sciences - may be coming to an end. Some physicists believe they are on the brink of finding a Theory of Everything which will describe all the forces and particles of nature in one equation that could be written on a T-shirt. Yet such an equation would not be the last word. You would still have to explain the complexity of the universe.

It is all very well speculating about probing deeper into the structure within the atom, but what about the structure in the universe at large? If the universe began in the hot fireball of a big bang some 15 billion years ago (as an overwhelming weight of evidence still suggests), how did it evolve to produce galaxies and stars, planets and people?

So, forget the end-of-science polemics. The most important science book published in 1997 carries the opposite message and a startling title, The Life of the Cosmos. It comes from Lee Smolin, a physicist based in New York, and it elaborates a theme developed over the past few years by Smolin himself, Andrei Linde in California, and a handful of other researchers. Their thesis is that the way the universe works can best be understood not simply by applying the rules of physics worked out by Newton and Einstein, but by taking account as well of the rules of evolution worked out by Darwin - the theory of natural selection. The universe and its main components (notably galaxies such as our own Milky Way) may literally be alive, and have evolved by natural selection from a simpler state to produce the complexity we see around us.

To take literally the equations of the general theory of relativity, the big bang itself emerged from a point of infinite density known as a singularity. There is another place where singularities occur: at the heart of a black hole. As Roger Penrose and Stephen Hawking proved in the Sixties, the expanding universe is described by exactly the same equations as a collapsing black hole, but with the opposite direction of time.

As far as I am aware, I was the first person to describe the universe as the inside of a black hole, in an unsigned editorial commentary in Nature. If all the complexity of galaxies, stars, planets and organic life has emerged from the singularity in which our universe was born, within a black hole, could not something similar be happening to the singularities at the heart of other black holes?

The most basic view of what might happen to a collapsing singularity to turn it into the kind of expanding singularity that we see in our universe is that there is simply a "bounce," turning collapse into expansion. Unfortunately, that will not do as an explanation. A singularity forming from a collapse within our three dimensions of space and one of time cannot turn itself around and explode back outwards in the same three dimensions of space and one of time. But in the Eighties, relativists realised that there is nothing to stop the material that falls into a singularity from being shunted through a kind of spacetime warp and emerging as an expanding singularity in another set of dimensions - another spacetime.

Mathematically, this "new" spacetime is represented by a set of four dimensions (three of space and one of time) just like our own but with all of the new dimensions at right-angles to all of the familiar dimensions of our own spacetime. Every singularity, on this picture, has its own set of spacetime dimensions, forming a bubble universe within the framework of some "super" spacetime, or superspace.

The dramatic implication is that many - perhaps all - of the black holes that form in our universe may be the seeds of new universes. And, of course, our universe may have been born in this way out of a black hole in another universe. This means that the universe may not be unique. Instead, it may be one of a population of universes, interconnected by what physicists call wormholes. The key element that Smolin has introduced into the argument is the idea that every time a black hole collapses into a singularity and a new baby universe is formed, the basic laws of physics are altered slightly as spacetime itself is crushed out of existence and reshaped. The process is analogous (perhaps more than analogous) to the way mutations provide the variability among organic lifeforms on which natural selection can operate. Each baby universe is, says Smolin, not a replica of its parent, but a slightly mutated form.

The original, natural state of such baby universes is to expand out to only about the Planck length (ie, the smallest scale on which any particle could have a meaningful existence), before collapsing once again. But if the random changes in the workings of the laws of physics - the mutations - happen to allow a little bit more expansion, a baby universe will grow a little larger. If it becomes big enough, it may separate into two, or several different regions, which each collapse to make a new singularity and thereby trigger the birth of a new universe. Those new universes will also be slightly different from their parents. Some may lose the ability to grow much larger than the Planck length and will fade back into the quantum foam. But some may have a little more inflation still than their parents, growing even larger, producing more black holes and giving birth to more baby universes in their turn. The number of new universes produced in each generation will be roughly proportional to the volume of the parent universe. There is even an element of competition involved, as the many baby universes are in some sense vying with one another; jostling for spacetime elbow-room within superspace.

Heredity is an essential feature of life, and this description of the evolution of universes works in a similar manner to living systems. On this picture, universes pass on their characteristics to their offspring with only minor changes, just as people pass on their characteristics to their children with only minor changes.

Universes that are "successful" are the ones that leave most offspring. Provided that the random mutations are indeed small, there will be a genuinely evolutionary process favouring larger and larger universes. Once universes start to be big enough to allow stars to form, in succeeding generations of universes there will be a natural evolution, a drift in the laws of physics, to favour the production of the kinds of stars that will eventually form black holes.

The end product of this process should be not one but many universes which are all about as big as it is possible to get while still being inside a black hole, and in which the parameters of physics are such that the formation of stars and black holes is favoured. Our universe exactly matches that description.

This explains the otherwise baffling mystery of why the universe we live in should be "set up" in what seems, at first sight, such an unusual way. Just as you would not expect a random collection of chemicals to organise themselves suddenly into a human being, so you would not expect a random collection of physical laws emerging from a singularity to give rise to a universe such as the one we live in. Before Darwin and Alfred Wallace came up with the idea of natural selection, many people believed that the only way to explain the existence of so unlikely an organism as a human being was by supernatural intervention; recently, the apparent unlikelihood of the universe has led some people to suggest that the big bang itself may have resulted from supernatural intervention. But there may no longer be any basis for invoking the supernatural. We live in a universe which is exactly the most likely kind of universe to exist, if there are many living universes that have evolved in the same way that living things on Earth have evolved.

The fact that our universe is "just right" for organic life-forms such as ourselves turns out to be no more than a side-effect of the fact that it is "just right" for the production of black holes and baby universes. Cosmologists are now having to learn to think like biologists and ecologists, and to develop their ideas not within the context of a single, unique universe but of an evolving population of universes. Each universe starts from its own big bang, but all the universes are interconnected in complex ways by black hole "umbilical cords," and closely related universes share the "genetic" influence of a similar set of physical laws.

But the realisation that our universe is just one among many, that it is alive and that no supernatural influences need be invoked to explain its existence is still not the most dramatic conclusion we can draw from the new cosmology. It is clear that the universe has not been set up for our benefit, and that organic life-forms on Earth are a minor side- effect of an evolutionary process involving universes, galaxies and stars. Nevertheless, the existence of life-forms such as ourselves is an inevitable side-effect of those greater evolutionary processes.

The same laws of physics apply throughout our universe and many other universes besides. Organic (carbon-based) material occurs in profusion between the stars of a spiral galaxy such as our Milky Way. This carbon- rich material seems to be crucially involved in the processes that allow gas clouds to cool and new stars to form, so a universe that is good at making black holes will also be good at making carbon-based compounds. Those compounds will undoubtedly seed any Earth-like planet that forms with each new generation of stars.

Astronomers calculate that there may be as many as 1020 planets suitable for life-forms such as ourselves. We see the components of organic life everywhere in the universe, and chances are that most of these 100,000,000,000,000,000,000 planets actually are carriers of our kind of life, in the same way that Earth is a carrier of life. The birth of the living universe inevitably gave rise to the birth of living planets. Which still leaves physicists the task of explaining just how complexity arose in a hot universe expanding out of a big bang. The end of science has been exaggerated. Indeed, you ain't seen nothin' yet.

This is an edited extract of an article appearing in the May edition of `Prospect'. `The Life of the Cosmos' by Lee Smolin will be published by Weidenfeld & Nicolson on 29 May.