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Cosmic Evolution by Eric Chaisson, Harvard University Press, £18.50,
ISBN 067400342X

THE Universe is a conspiracy to defeat the degradations of time. It achieves
this end by delaying the arrival of thermal equilibrium with an array of
devices. Nuclear forces, rotational motions, energy exchanges and, ultimately,
the expansion of the Universe as a whole—all play their part in keeping
the Universe an interesting place for billions of years longer than it ought to
be. Within the smooth sea of material in the Universe, small variations grow as
time passes and develop steep gradients in density, temperature and pressure.
Islands of denser material condense and merge, forming galaxies, stars, planets
and—quite recently—people.

In Cosmic Evolution, Eric Chaisson presents this thermodynamic saga
as a single, seamless story of energy flow and entropic gymnastics. This is
ambitious, but it’s an important step: usually we get the tale told from just
one viewpoint at a time.

He makes a good job of weaving the entire story of complex evolution into a
single picture by unifying the whole under the theme of energy flow density. And
what is this phenomenon? None other than that physical quantity familiar to
astronomers as light-to-mass ratio. In Cosmic Evolution it’s used as a
simple measure of the rate at which systems utilise energy. But Chaisson gets
into less well-charted territory when he argues that energy flow density is a
reliable measure of complexity across the physical spectrum.

His premise is that high energy flow density means high complexity, so as
time passes, nature’s evolutionary arrow will point towards systems of
ever-higher complexity. He makes the case with interesting, simple calculations
of the energy consumption rates for plants and animals. To this he adds a study
of human activities of varying complexity, and the arithmetic of the food chain.
For example, in a year, a human might be supported by 300 fish, which eat 90,000
frogs, which eat 27 million grasshoppers, which devour 1000 tonnes of grass,
whose calorific value ultimately derives from the solar flux.

But like all attempts to capture something as diverse as complexity within a
single parameter, there are limitations. One of the biggest limitations is the
fact that energy flow measures reward inefficiency. Without a separate criterion
for assessing complexity, it’s all too easy to attribute high complexity where
there is only high energy consumption, as in a supernova explosion or even the
entire Universe. Also, when energy-consuming systems, such as bacteria or
nanotechnologies, become very small other quantum constraints enter the picture
to limit their size and power.

Chaisson’s fluent and accessible style hovers between the pop-sci and the
technical. But there is sometimes a problem of information flow density: at
times Chaisson tries to pack a little too much into too few pages, leaving the
reader feeling that facts and figures are there for the sake of completeness
rather than out of necessity.

An arguably bigger problem is that the field itself is at the lively debate
stage, so some of the late-breaking news in Chaisson’s notes tell a different
story from the main text. The most conspicuous example is that of the
cosmological constant’s possible role in the expansion of the Universe. This is
ruled out as unwanted by astronomers and unmotivated by physics in the main
text, but the notes report that recent observational evidence shows it plays a
major role.

That said, Cosmic Evolution is an illuminating book, and one that
should appeal to both scientists and general readers. Seeing how the expansion
of the Universe spawned all the living, evolving complexity around and within us
creates a fuller appreciation of the entwined laws and flaws of Nature. At the
very least, this is a book that will encourage a greater energy flow between
astrophysics and bioscience.