The living Universe
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- Date: 15 Jul 2006 20:47:08 +0200
The birth of the living Universe
John Gribbin PEOPLE are only slowly coming to terms with the full
implications of the COBE satellite's discovery of ripples from the birth
of the Universe. One of the most startling is that our Universe may be
just one among many, and that it has "evolved" from simpler forebears --
that it is, in some sense, alive.
Among other things, the COBE data seem to confirm that the Universe
emerged from a period of exponential expansion, known as inflation, at
about the time those ripples were imprinted on the background radiation.
At first sight, though, 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 can form. A
shorter, less intense burst of inflation would have left the proto-
universe too jumbled up, and also in danger of quickly recollapsing back
down into a singularity, while 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.
This fine-tuning problem is generally regarded as the biggest difficulty
with inflation. The problem is essentially another example of the
Goldilocks effect -- why is inflation, like so many other properties of
the Universe, "just right" to allow our (the Universe's) existence?
But the simplest version of inflation, complete with the fine-tuning
problem, can explain everything we can see, including the ripples in the
cosmic background radiation. And the fine-tuning problem itself can be
resolved once we realise that the Universe itself is alive and has
evolved.
Almost halfway through the 1990s, it seems that we know, more precisely
than anybody has ever known before, what the Universe is made of, as well
as how the Universe came into existence. "Dark matter", sufficient to make
the Universe closed upon itself like a black hole, is required to explain
how galaxies move, and the COBE ripples; it is just a matter of time
before the nature of the dark matter is revealed (indeed, some may already
have been detected -- Science, 25 September). And we know that the
ultimate fate of the Universe itself is that one day the present expansion
will be first halted and then reversed, so that it collapses back into a
singularity that is a mirror image of the one that gave it birth.
We actually live inside a huge black hole. And what's more, we have a
pretty good idea of what happens to anything that collapses towards a
singularity inside a black hole.
The idea of the Universe as a black hole is not new, although until
recently it was distinctly unfashionable. In the 1980s 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 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, which we can refer to simply as
"superspace".
One way to picture what this involves is to use the old analogy between
the three dimensions of expanding space around us and the two-dimensional
expanding surface of a balloon that is being steadily filled 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 black hole as forming from a tiny pimple 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. There is a new 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 at all. There can be many bubbles
growing out of the skin (the spacetime) of the original universe in this
way at the same time. And, of course, new bubbles can grow out of the skin
of each new universe, ad infinitum.
Instead of the collapse of a black hole representing a one-way journey to
nowhere, many researchers now believe that it is a one-way journey to
somewhere -- to a new expanding universe in its own set of dimensions.
Instead of a black-hole singularity "bouncing" to become an exploding
outpouring of energy blasting back into our Universe, it is shunted
sideways in spacetime.
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 own Universe may have been born in this way out of a black
hole in another universe. While the fact that the laws of physics in our
Universe seem to be rather precisely "fine tuned" to encourage the
formation of black holes means that they are actually fine-tuned for the
production of more universes.
This is a spectacular shift of viewpoint, which most cosmologists are
still struggling to come to grips with. 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 spacetime (perhaps better regarded as cosmic umbilical
cords) that join a "baby" universe to its "parent".
It is relatively easy to see how such a family of universes can continue
to exist, and to reproduce, once something like our own Universe exists.
But how did the whole thing get started? Where did the first universe, or
universes, come from?
The key concept is quantum uncertainty. This says that there is always an
intrinsic uncertainty in many physical properties of the Universe and
things in the Universe. The most commonly quoted example is the
uncertainty that relates the position of a particle to its motion.
Momentum is a measure of where a particle is going, and quantum
uncertainty makes it impossible to measure the position of, say, an
electron and its momentum at the same time. This is not a result of the
inadequacies of our measuring equipment, but a fundamental law of nature,
which has been thoroughly tested and proved in many experiments. An object
like an electron simply does not have both a precise momentum and a
precise position.
Another pair of uncertain variables linked in this way is energy and time.
Again, the uncertainty only applies on a subatomic scale, as far as any
practical consequences are concerned. But what quantum physics tells us is
that any tiny region of the vacuum, which we think of as "empty space",
might actually contain a small amount of energy for a short time. In a
sense, it is allowed to possess this energy if the Universe doesn't have
time to "notice" the discrepancy. The more energy there is involved, the
shorter the time allowed. But because particles are made of energy (E =
mc2), this means that particles are allowed to pop into existence in the
vacuum of empty space. They are made out of nothing at all, and can only
exist provided that they pop back out of existence again very quickly.
On this picture, the quantum vacuum is a seething froth of particles,
constantly appearing and disappearing, and giving "nothing at all" a rich
quantum structure. The rapidly appearing and disappearing particles are
known as virtual particles, and are said to be produced by quantum
fluctuations of the vacuum.
It may seem that quantum theory has run wild when pushed to such extremes,
and common sense might tell you that the idea is too crazy to be true.
Unfortunately for common sense, these quantum fluctuations have a
measurable influence on the way "real" particles behave. The nature of the
electric force between charged particles, for example, is altered by the
presence of virtual particles, and measurements of the nature of the
electric force show that it matches the predictions of quantum theory,
rather than matching up to the common sense way it would behave in a
"bare" vacuum.
What has all this got to do with the creation of universes? It all hinges
upon the fact that we live inside a black hole. In 1973, Edward Tryon, of
the City University of New York, suggested that our entire Universe might
simply be a fluctuation of the vacuum (Nature, vol. 246, p. 396). He
pointed out the curious fact that our Universe contains zero energy --
provided it is indeed closed and forms a black hole. The point Tryon
jumped off from -- the secret of making universes out of nothing at all,
as vacuum fluctuations -- is that the gravitational energy of the Universe
is negative.
The way to understand this is that if you think of a collection of matter,
such as the atoms that make up a star, or the bricks that make up a pile,
the "zero of gravitational energy" associated with those objects is when
they are far apart -- as far apart as it is possible for them to be. The
strange thing is, as the objects fall together under the influence of
gravity they lose energy. They start with none, and end up with less. So
gravitational energy is negative, from the perspective in which everyday
energy (the mc2 in those atoms and bricks) is positive. Any object in the
Universe, like a planet, or the Sun, which is not spread out as far as
possible literally has a negative amount of gravitational energy. And if
it shrinks, its gravitational energy becomes more negative.
The reason this was so interesting to Tryon is that the energy of all the
matter in the Universe, all the mc2, is positive. What's more, if you take
a lump of matter and squeeze it into a singularity, then at the
singularity the negative gravitational energy of the mass is exactly equal
and opposite to its mass energy.
Jordan's idea will not work for the formation of a star, because any star
trying to form from a singularity in this way will be inside a black hole,
invisible to the Universe at large. But it will work for the creation of
an entire universe, within the black hole.
Provided that the Universe is indeed closed, like the inside of a black
hole, the energy involved in making a universe from a singularity is
indeed zero! It is, in the words of Alan Guth, "the ultimate free lunch".
Quantum uncertainty allows bubbles of energy to appear in the vacuum, and
energy is equivalent to mass. According to the rules of quantum
uncertainty, the less mass-energy such a bubble has, the longer it can
exist. So why couldn't a bubble with no overall mass- energy last forever?
The snag with all this, and the reason why Tryon's idea didn't cause much
of a stir in 1973, is that whatever the quantum rules may allow, as soon
as a universe containing as much matter as ours does start to expand away
from a singularity, its enormous gravitational force (imagine the pull of
gravity associated with an object containing the entire mass of the
Universe in a volume smaller than an atomic nucleus) would pull it back
together and make it collapse back into a new singularity in far less than
the blink of an eye.
What Tryon was saying, in effect, was that not just virtual particles but
virtual universes might be popping in and out of existence in the vacuum.
In 1973, he had no idea how such a virtual universe might be made real.
But inflation provides a mechanism which can catch hold of a tiny,
embryonic universe during that split second of its virtual existence, and
whoosh it up to a respectable size before gravity can do its work. Then,
it will take billions (or hundreds of billions) of years for gravity to
slow the expansion, bring it to a halt, and make the universe contract
back into a singularity.
In the 1980s, this idea of a universe being created out of nothing at all
was developed by many researchers, including Tryon himself, Guth, and Alex
Vilenkin, of Tufts University. The consensus is that yes, indeed,
universes can be born out of nothing at all as a result of quantum
fluctuations. And the same powerful influence of inflation can transform
any baby universe in the same way -- it doesn't matter how much, or how
little, matter goes into a black hole to make the singularity; once the
new singularity starts expanding into its own set of dimensions to make a
new universe, the balance between mass energy and gravitational energy
means that the new universe can be any size at all.
But there is still a puzzle of fine-tuning, because there is no obvious
reason why inflation itself should have just the right strength to "make"
a universe like our own out of a tiny quantum fluctuation of the vacuum.
The "natural" size for a universe is still down in the subatomic region
where quantum effects rule, on the scale of the Planck length, 10-35 of a
metre. This is where evolution comes in. Nobody would argue, these days,
that human beings appeared out of nothing at all on the face of the Earth.
We are complex creatures that could not arise "just by chance" out of a
brew of chemicals, even in some warm little pond. 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.
The new understanding of cosmology suggests that something similar has
happened with the Universe. It is a large and complex system, which cannot
have appeared "just by chance" out of a random quantum fluctuation of the
vacuum. Simpler universes came first, and it may have taken hundreds of
millions of universal generations to progress from a Planck-length
fluctuation to complex universes like our own. Lee Smolin, of Syracuse
University, has been a leading protagonist for this idea, which also takes
on board notions about baby universes developed by Andrei Linde, of the
Lebedev Institute, in Moscow.
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 life forms on which natural selection can
operate. Each baby universe is, says Smolin, not a perfect replica of its
parent, but a slightly mutated form.
The original, natural state of such baby universes is indeed to expand out
to only about 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
several, different regions, that 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 that are
produced in each generation will be roughly proportional to the volume of
the parent universe. There is even an element of competition involved, if
the many baby universes are in some sense vying with one another, jostling
for spacetime elbow room within superspace.
In his published papers, even Smolin has stopped short of suggesting that
the Universe is alive. But heredity is an essential feature of life, and
this description of the evolution of universes only works if we are
dealing with 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.
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 (as nearly flat as possible), 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 suddenly 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.
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; 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 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.
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 in the context 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. The ripples in time traced out by the
sensors on board COBE are, on this new picture, just a tiny part of a much
more complex and elaborate structure, a structure which maintains itself
far from equilibrium, and in which universes in which the laws of physics
resemble those in our Universe are far more common than they ought to be
if those universes had arisen by chance.
The COBE discoveries do not mark the end of the science of cosmology, but
the beginning of a new science of cosmology, much bigger in scope, probing
further in both space and time than cosmologists could have imagined even
a few years ago.
http://www.lifesci.sussex.ac.uk/home/John_Gribbin/tlu.htm
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