Book review by Anthony Campbell. Copyright © Anthony Campbell (2004).

Information is a buzzword whose meaning one might expect to be obvious
to everyone, judging from the frequency with which it is used. In fact,
however, von Baeyer tells us at the outset that we don't actually know
what information **is**, even though we can treat it mathematically
with great precision and can measure, market, regulate and tax it. In
this respect it resembles another equally abstract quantity, energy. The
concept of energy was analysed by physicists in the nineteenth century;
information theory is a twentieth-century contribution. But the message
that emerges from von Baeyer's book is that we are only at an early
stage in our understanding of the concept. which is now beginning to
ramify throughout the whole way in which we think about the natural
world.

Quite early on in this book it becomes clear that von Baeyer is writing
about the fascinating, if very abstract and difficult, boundary
that lies between science and philosophy. At the conclusion of his
opening section he brings up the celebrated dispute between Einstein and
Bohr concerning the right way to think about nature. Einstein held that
science ought to be able to tell us what things are, whereas Bohr
"believed that physics is not about ontology, the science of essences,
but about epistemology, the study of how we know what we know, and of
the the limitations to our knowledge." Bohr's philosophical position,
von Baeyer tells us, can be generalized to include not just physics but
all of science, and *science is about information*. The whole
book is really concerned with bringing out the implications of this
statement.

The development of information theory in the twentieth century came about thanks to Claude Shannon, who gave mathematical expression to ideas that had hitherto been expressed only vaguely, in verbal descriptive terms. Many other mathematicians, however, as far back as the seventeenth century, when probability theory was first developed, have played a part in shaping the classical notion of information. Von Baeyer provides an outline of how information theory underlies a number of scientific fields, including that most fundamental idea of classical physics, entropy.

One important concept that developed in information theory in the
twentieth century was that of *noise*. We usually think of this
purely as a nuisance, and engineers spend much time and ingenuity trying
to minimize its effects in their systems, but von Baeyer makes the
important point that noise is not merely unavoidable but is actually
indispensable. Without it, we would be overwhelmed by an irresistible
flood of information that would require an infinite amount of memory and
time to process.

In a sense, all the material that has been discussed up to this point is really a preliminary to what von Baeyer sees as the real importance of the information concept, which is its relevance to the quantum world. The key word in all this is the qubit, a contraction of "quantum bit". Von Baeyer pens a near-poetic description of this elusive object, which he pictures as "a soft, translucent sphere, a peeled seedless grape shimmering indistinctly in all the colours of the rainbow at once … an inexhaustible source of possibilities from which only one can finally be realized."

Many of us, I suppose, tend to think of quantum phenomena as taking place at an unimaginably tiny scale and as having no direct connection with the everyday world in which we live. But von Baeyer insists that this is the wrong way to view the matter. "The burning question for physics has become: how come we don't notice superposition in everyday life? or: how are the superpositions of the world at its fundamental level disguised to yield the stark outlines of the world our senses perceive?" The application of information theory to this question, he suggests, will ultimately provide an answer, though we may have to wait for the development of quantum computers for this to become available.

In the meantime, von Baeyer sees a pointer to how things may develop in
the work of Anton Zeilinger, Professor of Experimental Physics at the
University of Vienna. His experiments indicate that quantum effects are
not confined to very small objects like photons but can be demonstrated
to affect even buckyballs, large molecules containing 60 or 70 carbon
atoms. It seems that viruses will be next. Zeilinger is now working on a
theoretical approach to quantum mechanics, which he encapsulates in the
gnomic utterance: *An elementary system carries one bit of
information*. When expanded, this takes us back to Bohr and his
insistence that physics in general and quantum mechanics in particular
do not describe the world in itself but only what we can say about it.

This is a profound book, and, it must be said, not an easy one. The difficulty does not lie in von Baeyer's writing, which is commendably clear. But the ideas are intrinsically difficult and the reader needs to do quite a lot of work to grasp them. In one or two places, notably the description of a game involving the making of bead necklaces, which von Baeyer uses to illustrate quantum superimposition, the limits of non-mathematical exposition are reached and perhaps even surpassed; some diagrams might have helped. But the journey through these strange lands of thought is very much worth the undertaking.

%T Information

%S The new language of science

%A von Baeyer, Hans Christian

%I Weidenfeld and Nicolson

%C London

%D 2003

%G ISBN 0-297-60725-1

%P xiv + 258 pp

%K science

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