Book review: A Universe Tuned for Life

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A Universe Tuned for Life
John Pea***

The Cosmic Landscape: String Theory and the Illusion of Intelligent
Design. Leonard Susskind. xii + 403 pp. Little, Brown, 2006. $24.95

Does God exist? Most scientists would probably prefer to avoid
confronting this question in their professional lives, but the growth
of the "intelligent design" movement makes it harder for them to
maintain such distance. Intelligent design appears to be a rediscovery
of the 19th-century argument from design, which perceived the manifest
hand of a Creator in complex biological mechanisms such as the eye. The
fallacy in this view is well exposed in, for example, Richard Dawkins's
The Blind Watchmaker, which details how evolution can yield living
structures of almost arbitrary complexity from a basic set of building
blocks. The genetic record essentially exhibits this process at work,
including the sobering fact that you and I share more than 20 percent
of our genes with worms. Nothing in life is certain, but our common
genetic heritage with such primitive creatures is surely proof beyond
reasonable doubt of the operation of evolution. The fact that this
assertion can be disputed is a disturbing symptom of the growth of
irrationality in the modern world.

Even if the evolution-deniers could be persuaded of their errors,
however, the intelligent-design argument would still need to be
confronted on a wider stage. A cursory search of the Internet yields
many who think that the Earth is surprisingly well fitted for life and
that this happy situation must result from the efforts of a designer.
Most astronomers would say that, on the contrary, this match between
our biological needs and the nature of the Earth is the result of a
simple selection effect: There exist innumerable planets, and life will
not be found on those that are too hot or too cold. The bias that
arises from selection effects is often called "anthropic," although
this is an unfortunate name because it apparently implies that the
universe wants to create creatures like us, whereas the existence of
life on Earth is a random outcome of the disinterested laws of physics
and probability.

In an everyday analogy, winning the lottery does not prove that God
exists (although it might feel that way to you). After all, there were
many other ticket holders who were unsuccessful. In the same way, we
could have inferred that the universe is probably full of planets at
varying distances from their central stars long before we had the
telescopes to detect them.

So far so good, but we are not finished. There are aspects of the laws
of physics themselves that seem puzzling when the origin of life is
considered. A good example is Fred Hoyle's discovery that stars very
nearly fail to make carbon and that only a peculiar coincidence in
excited energy levels permits this process to happen. More radically,
cosmologists have established over the past decade that the energy
density of the vacuum is not zero: Perfect emptiness still weighs
something, impossible though that sounds. The energy density of the
vacuum is tiny compared with the result of any attempt to predict it
using particle physics, but this fact is a good thing: Galaxies, stars
and planets would fail to form if the vacuum density were much higher
than the observed level. This conclusion, which no scientist contests,
sounds like intelligent design on the largest scale-the whole
universe being carefully set up so that we could come into being. It
seems as though, in Hoyle's words, "a superintellect has monkeyed with
physics." Could this be true?

At first sight, this ultimate design argument does seem impressive. But
a consideration of why Earth is amenable to life suggests a way out of
the paradox. Recall that it is the diversity of planets that allows
selection of the environments that best match life in general. The
resulting conclusion is inevitable: If the laws of physics seem
strangely tuned to permit the creation of life, there must exist an
ensemble of universes with a variety of laws of physics.

The idea that many different laws of physics are possible has been the
subject of speculation for years, but a firmer foundation has emerged
recently from string theory, the "theory of everything" in physics. As
a leading string theorist, Leonard Susskind is well placed to explain
these developments. In 2003 (see http://arxiv.org/abs/hep-th/0302219),
he coined the term landscape to summarize two related ideas. The first
is that the mathematical edifice of string theory predicts many
possible consistent laws of physics, not only the ones that we happen
to observe. Furthermore, it is possible within modern inflationary
cosmology to have a "multiverse" where all these possibilities actually
exist in different regions. Not all string theorists accept this
conclusion; if true, it represents the crushing of their dream that
string theory would ultimately explain why nature has had to function
in the way that it does.

Because the landscape idea has broad implications, it is good to see
that in his new book, The Cosmic Landscape, Susskind has cast the
arguments into a form suitable for a general readership. It is clear,
though, that Susskind is not just intent on educating readers-he
wants to pick a fight. The subtitle of his book is String Theory and
the Illusion of Intelligent Design. This is not just entertainment for
the scientifically curious lay reader but also opposition to the whole
march of religious fundamentalism. Susskind lays out his position from
the start, with a quote from Laplace about having no need for the
hypothesis of God. This confrontational approach will probably do no
harm to sales.

To present his case, Susskind has to outline particle physics as far as
the Higgs field, introduce the main landscape idea by exploring the
consequences of varying the Higgs field, explain why the Standard Model
is too complicated to be fundamental, explain string theory and its
history, and justify in terms of the topology of Calabi-Yau manifolds
why there are so many possible incarnations of particle physics. On the
way, he has to explain most of cosmology-how we know there is vacuum
energy, why inflation was invented as a theory of initial conditions
and how inflation allows for an ensemble of universes. Finally, he has
to explain the general idea of the anthropic principle and show how
observational selection can exploit the string/inflation ensemble of
different universes with differing laws of physics, so that we find
ourselves in a universe tuned for life, without the slightest need for
a divine guiding hand.

Covering all of this territory in less than 400 pages is a huge
challenge, one that Susskind meets extremely well. He uses helpful
diagrams and vivid analogies to illuminate the concepts. And the
structure of the book is engagingly quirky. Susskind mixes explanation
with personal anecdote and interleaves different topics so that the
reader doesn't become disheartened by having to follow a long and
complex argument all in one go. This is not to say that the average
reader will find the book simple to absorb, because there is a lot to
take in-both in terms of concepts and of history. One of the many
virtues of Susskind's presentation is that it gives some good insights
into the history of string theory, starting with its origins as an
attempt to model strongly interacting particles as rubber bands.

Nothing is perfect, of course. Some of the key points really need a
longer explanation in order to make sense to an unprepared reader. I
think anyone coming fresh to the cosmological constant here would
struggle, for example, especially as the idea of this long-range
repulsion is introduced before any of the other material about
cosmology. Also, Susskind is sometimes happy to use more sophisticated
concepts that may stump nonmathematical readers. An example is plotting
a "two-dimensional" landscape as a surface with the Higgs field
depending on x and y coordinates that are the electric and magnetic
field strengths. This leap of casting the quantity of interest as an
abstract space is automatic to a physicist, but a little more sympathy
for the novice at such points might have helped.

Also, I was less than happy with some of the description of cosmology.
Susskind seems to think that astronomical data have confirmed the
reality of inflation, which is not so (although inflation is
undoubtedly consistent with current observations). In terms of history,
Edwin Hubble gets the usual overexposure, and it was amusing to read a
detailed description of how Hubble measured redshifts, whereas in fact
almost every redshift Hubble used was measured by Vesto Slipher, who
had established the general tendency for galaxies to be redshifted by
1917 (compare Susskind's assertion that in 1917, "as far as [Einstein]
or anyone else knew, the galaxies were stationary").

Finally, the language of the book will often seem a little cryptic to
non-American readers: What is a BB ball? At least a "Rube Goldberg
machine" is explained in the index, although all British readers will
of course know that the inventor of absurdly elaborate machines was
Heath Robinson, who was Goldberg's elder by nine years.

These obligatory small criticisms should in no way detract from
Susskind's tremendous achievement. This book is a fine piece of popular
science writing, but it is particularly significant for the timeliness
of its message. Susskind emphasizes that the whole structure of the
universe requires an active Creator no more than does the human eye or
the temperature of the Earth. At a time when more and more people seem
happy with a creation that took place 6,009 years ago, this lesson
needs repeating.

In the end, however, good though this book is, I was left feeling that
the argument was not carried to its logical conclusion. Despite his
justified scorn for intelligent design, Susskind retains a hint of this
worldview in his own attitude. It was Galileo who said that the book of
Nature is written in mathematics, and almost all physicists subscribe
to this view. When we contemplate the power and simplicity of
constructions like general relativity, there is a temptation to carry
intelligent design to an extreme in which God wrote the equations, from
which all else follows. Frequently this perspective is quite explicit,
as with Einstein (recall Bohr's admonition, "Stop telling God what to
do!"). The landscape picture derails this thinking to some extent, but
Susskind just transfers the quasi-religious awe to string theory, whose
mathematical results he repeatedly describes as "miraculous."

But if life on Earth is a random accident in a universe where only
chance yielded laws of physics suitable for life, why stop there?
Perhaps string theory itself is nothing special and only part of a
wider spectrum of possible prescriptions for reality. If the search for
a unique and inevitable explanation of Nature has proved illusory at
every step, is it really plausible that suddenly string theory can make
everything right at the last? Reading Susskind's book should make you
doubt that possibility, in which case we may have reached the end of
the search for underlying simplicity that has driven physics since the
beginning. A comment made by Steven Weinberg in his 1977 book The First
Three Minutes sums things up well: "The more the universe seems
comprehensible, the more it also seems pointless." Pointless to look
for meaning in our existence in the universe, and also (according to
Susskind) pointless to look for meaning in physics. To a physicist,
this is a pretty depressing conclusion, but there is some consolation:
The beauty we perceive in the laws of physics perhaps tells us as much
about the human aesthetic response as it does about any fundamental
design of the universe. In short, physics is a human creative art on
the same level as painting and music, and that is reason enough to be
proud of what the subject has achieved.
Reviewer Information

John Pea*** is a professor of cosmology and postgraduate coordinator
in the Institute for Astronomy at the University of Edinburgh. His
research interests, which are in theoretical and observational
cosmology, include large-scale structure, galaxy formation and
evolution, evolution of active galaxies, and gravitational lensing.

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