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Nobody would argue that human beings appeared out of nothing. We are
complex creatures, and could not have arisen ‘just by chance’ out of a brew
of chemicals, even in some warm little pond of the kind envisaged by Charles
Darwin. Simpler kinds of living organisms came first, and it took hundreds
of millions of years of evolution on Earth to progress from single-celled
life forms to complex organisms like ourselves.

Could something similar have happened with the Universe? It is a large
complex system which, some cosmologists argue, cannot have appeared by chance.
Simpler universes came first, they say, and it may have taken hundreds of
millions of universal generations to progress to a universe as complex as
our own.

Lee Smolin, professor of physics at the Center for Gravitational Physics
and Geometry at the Pennsylvania State University, is a leading proponent
of this idea, which also takes on board notions about baby universes developed
by Andrei Linde of the Lebedev Physics Institute in Moscow and Stephen Hawking
of the University of Cambridge. One of the jumping off points for such speculation
is that the Universe we see around us seems to be in a very peculiar state,
not ‘typical’ of the way a universe might be expected to emerge from a big
bang. According to the basic laws of physics, universes should be much
smaller and shorter-lived.

The puzzle has become more pressing as evidence has mounted that the
Universe really did emerge from a big bang some 15 billion years ago. The
evidence suggests that the Universe was born out of a singularity – a point
of infinite density occupying zero volume – and that in the first split
second the tiny seed containing all the mass and energy in the observable
Universe went through a period of exponential expansion, known as inflation.

The key feature of inflation is that it stretches space-time – the three
dimensions of space together with time – by a very large amount, smoothing
out any irregularities that are present. Think of the difference between
the wrinkled skin of a dry prune and the smooth surface of the same prune
when it has absorbed its fill of water, then picture how smooth the skin
of the prune would be if it were inflated to the size of the Earth, and
you get some idea of how the process works.

But cosmic inflation happened on a much smaller scale, and had ended
by the time the Universe reached the size of a grapefruit. Around this time,
matter was distributed evenly – but not perfectly evenly. There were small
irregularities, or clumps of matter. Once inflation slowed, these clumps
had enough gravity to gather other matter around them. Since then, more
leisurely inflation has taken 15 billion years to expand the grapefruit
to its present size, with the clumps of matter yielding galaxies, stars
– and people.

At first sight, there is no obvious reason why the inflation process
should have gone on for just long enough and at just the right rate to produce
a Universe in which stars and galaxies could form. A shorter, less intense
burst of inflation would have left the matter too jumbled up, and the proto-universe
in danger of quickly recollapsing back into a singularity. A longer, stronger
burst of inflation would have spread the stuff of the proto-universe so
thin that no stars and galaxies could ever form.

Goldilocks effect

This problem of fine-tuning is generally regarded as the biggest difficulty
with inflation. It is essentially an example of the Goldilocks effect: why
is inflation, like so many other properties of the Universe, ‘just right’
to allow our Universe to exist. But the fine-tuning problem can be resolved
by taking on board the idea that the Universe itself is alive and has evolved.

A key feature of the argument is that the birth of the Universe – an
outburst from a singularity – is essentially a mirror image of the collapse
of a massive object into a black hole, which is an implosion towards a
singularity. It is 30 years since Roger Penrose, now at the University of
Oxford, and Hawking established that the equations describing the big bang
expansion of the Universe are precisely the time-reverse of the equations
describing the collapse of a black hole. But it was only in the 1980s that
cosmologists realised that our Universe may contain so much material, most
of it in the form of invisible, dark matter, that one day the enormous gravitational
force would first halt the present expansion and then reverse it, making
the Universe collapse back into a singularity that is a mirror image of
the one that gave it birth.

At about the same time, relativists realised that there is nothing
to stop the material that falls into a singularity in our three dimensions
of space and one of time from being shunted through a kind of space-time
warp and emerging as an expanding singularity in another set of dimensions
– another space-time. Mathematically, this ‘new’ space-time is represented
by a set of four dimensions, just like our own, but with all the dimensions
at right angles to all the familiar dimensions of our own space-time. Every
singularity, on this picture, has its own set of space-time dimensions,
forming a bubble universe within the framework of some ‘super’ space-time,
which we can refer to simply as ‘superspace’.

One way to picture what this involves is to use the analogy between
the three dimensions of expanding space around us and the two-dimensional
expanding surface of a balloon steadily filling with air. The analogy is
not with the volume of air inside the balloon, but with the expanding skin
of the balloon, stretching uniformly in two dimensions but curved around
upon itself in a closed surface.

Imagine a tiny pimple forming on the surface of the balloon, a small
piece of the stretching rubber that gets pinched off and starts to expand
in its own right. It develops into a bubble, attached to the original balloon
by a tiny, narrow throat – the black hole. And this new bubble can expand
away happily in its own right to become as big as the original balloon,
or even bigger, without the skin of the original balloon (the original universe)
being affected.

There can be many bubbles growing out of the skin (the space-time) of
the original universe in this way at the same time, all interconnected
by a system of black hole ‘throats’ – referred to as wormholes or tunnels.
And new bubbles can grow out of each new universe, ad infinitum.

Instead of the collapse of a black hole representing a one-way journey
to nowhere, Hawking, Linde and Smolin and others suggest that it is a one-way
journey to somewhere – to a new expanding universe in its own set of dimensions.
The dramatic implication is that many, perhaps all the black holes that
form in our Universe may be the seeds of new universes. And, of course,
our own Universe may have been born in this way out of a black hole in another
universe. What’s more, it turns out that the fact that the Universe seems
to be so efficient at the job of making stars and turning them into black
holes means that it is also efficient at making more universes.

This is a spectacular shift of viewpoint, and most cosmologists are
still struggling to come to grips with it. If one Universe exists, then
it seems that there must be many – very many, perhaps even an infinite number
of universes. Our Universe has to be seen as just one component of a vast
array of universes, a self-reproducing system connected only by the tunnels
through space-time, which in this view are perhaps better regarded as cosmic
umbilical cords that join a baby universe to its parent.

But there is still a puzzle of why inflation should have just the right
strength to lead to a universe like our own. The ‘natural’ size for a universe
is down in the subatomic region, on the scale of the Planck length, 10 ^-35
of a metre, the smallest ‘distance’ that can exist. This is where evolution
comes in.

The key element that Smolin has introduced is the idea that every time
a black hole collapses into a singularity and a new baby universe is formed
with a new space-time, the laws of physics that are born with it are slightly
different. The force of gravity, for example, may be a little stronger
– or weaker – in the baby universes than in the parent. The process, he
argues, resembles the way mutations provide the variability among organic
life forms on which natural selection can operate.

Each baby universe, says Smolin, is not a perfect replica of its parent
but a slightly mutated form. The original, natural state of a baby universe
may indeed be to expand out to a few times the Planck length, 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 inflation, a baby universe
will grow a little larger. If it becomes big enough, it may separate into
two or more different regions that each collapse to make a new singularity
and thereby trigger the birth of another generation of universes.

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 realm. 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 that are produced in each generation will be roughly proportional
to the volume of the parent universe. ‘The essential point,’ says Smolin,
‘is that the universes that reproduce the most successfully by leaving
the largest number of progeny dominate the ensemble after many generations.’

The Universe within

The end product should be not one but many universes, 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 suddenly
to organise themselves 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 like the one we live in.

Smolin has stopped short of suggesting that the Universe is alive. But
heredity is one of the defining attributes of life, and Smolin suggests
that 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 in evolutionary terms
are the ones that leave the most offspring. Provided that the random mutations
are indeed small, there will be a genuinely evolutionary process favouring
larger and larger universes.

Smolin’s ideas are far from being accepted. One criticism is his assumption
that the physical laws a universe is born with will be only slightly different
from those of its parent; they could equally be very different or the same.
‘I don’t go along with all the details of Smolin’s argument,’ says Paul
Davies of the University of Adelaide, ‘but it’s a welcome new way of looking
at the old problem of why the Universe is as it is.’

Before Charles Darwin and Alfred Wallace came up with the idea of evolution,
many people believed that the only way to explain the existence of so unlikely
an organism as a human being was by supernatural intervention. The apparent
unlikelihood of the Universe has similarly led some people to suggest that
the big bang may have resulted from supernatural intervention. Even respectable
cosmologists such as Davies and Frank Tippler of the University of New Orleans
talk of the new cosmology as revealing ‘the mind of God’ at work.

But if Smolin is right, there is no longer 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.

Further reading: In the Beginning by John Gribbin (Viking 1993). For
a detailed exposition by Lee Smolin on his ideas on the living Universe,
see his 1992 paper in Classical and Quantum Gravity (vol 9, p 173) and the
Syracuse University preprint number SU-GP-91/10-5.