These dark materials

Simon Singh describes mankind's fascinating struggle to understand our increasingly improbable universe in Big Bang

Big Bang
by Simon Singh
544pp,Fourth Estate, £20

Simon Singh, in this very large book, presents a history of the evolving discovery of the universe from early historic times up to the 1990s. He shows how the term "universe" expanded in its definition from the Milky Way (some 100,000 light years across), through the realisation that we live in merely one "island universe" among many, with truly vast distances separating these islands. By the 1930s it had been discovered that these "islands" were indeed star systems, now called"galaxies".

Some galaxies are like our Milky Way, but most have very different shapes and sizes. Even more dramatically, the vast distances between these galaxies were observed to be increasing, with this expansion of the universe - by then redefined to include all of space-time - universally known as Hubble's law.

In parallel, the sun had been recognised as one star among very many, geologists had realised that our Earth was billions of years old, while nuclear fusion, transmuting the elements from hydrogen and helium into the stardust of oxygen and carbon, was identified as the energy source sustaining light and life for these eons. The origin of the chemical elements in stars was (more or less) understood by the 1960s, though it became apparent that hydrogen and helium must have a different, pre-stellar origin. This was soon known to be during the few minutes after the start of the Big Bang, the event in which space-time, and our universe, came into existence.

Through the 20th century a qualitative description of the objects - galaxies - that make up the visible universe was also becoming accepted. The new science of radio astronomy discovered enough hydrogen not yet formed into stars to show that the universe was roughly midway through its stellar-bright phase: by the 1960s it was known we were comfortably in orbit around a middle-aged star in a suburban part of an average galaxy midway through its life.

This Norman Rockwell-style universe soon collapsed under a barrage of unexpected discoveries: the residual heat from the Big Bang, itself the origin of the universe as we see it, was soon found (it is visible today as TV static), creating the science of origins, while technological advances allowed vastly improved direct study of the distant, and young, universe.

A huge convenience of observational astrophysics is the finite speed of light: as we look far away we unavoidably see objects as they were long ago, when the light left them. Thus astronomers see ancient objects as they were. By looking at different distances we see the evolving universe directly (raising fascinating issues about the meaning of "now"). These technological advances, however, finally forced astronomers to take our insignificance seriously. This "Copernican principle" reminds us we should not expect be too special: our eyes are adapted to detect predators (cave bears) and potential food, and not necessarily to allow an unbiased view of the nature of existence and energy. Remarkably, our minds can make this leap. Quantitative astrophysics soon discovered that what we see is not what we get: most matter does not shine in any waveband, light, heat, X-rays or radio. It is in fact dark. Ergo, dark matter.

The latest energy census suggests that everything which shines, and everything which is studied by scientists on Earth, is an almost irrelevant perturbation of reality. Matter like that of which we are constituted makes up a small percentage of the mass-energy of the universe. There is roughly 10 times as much dark stuff, of unknown nature but which is matter (it responds to and generates gravity), as there is stuff we can identify ("see").

Recently, amid much publicity, astrophysicists have discovered that there is roughly three times more of some other stuff, which is not matter, but which has pressure (it pushes, gravity pulls). This "dark energy" took control of the future of the universe around the time the sun and Earth were formed, and started accelerating the cosmic expansion. The universe today is expanding faster and faster, leading to a future that remains to be understood, but which may well be very lonely indeed. Exciting times.

By the 1990s, Singh tells us, the basic Big Bang model of the universe, with its many spectacular successes in describing what astronomers observe, was in place. Dark matter, dark energy and the continuing rapid progress in discovery, is summarised in an epilogue to Big Bang which claims that cosmology "evolves too rapidly for any book to be really up to date. The approach is based on brief biographies of key scientists through the discovery process: the book is a history of the key events in mankind's discovery of cosmology, and the current pre-eminence of the Big Bang model. It is not a history of the universe."

Singh tells his tale well, with chatty anecdotes leavening the astrophysics. Many highly motivated personalities are described - not all of whom separated personal dislike from professional competition. All, however, are keen scientists and are therefore subject to excitement, occasional success and - most of the time - frustrating hard work. One conspicuous and useful aspect of this book is the personalisation of the scientist and his/her motivation. I liked the quotation from Einstein: "I have no special talents: I am only passionately curious."

The great physicist Richard Feynman expressed the methodology of science beautifully: "It doesn't matter how beautiful your guess is or how smart you are or what your name is. If [your idea] disagrees with experience, it's wrong. That's all there is to it."

The progression of generation, testing, refuting, improving and developing ideas to understand the origin of everything is the story of this book. It is an interesting story. And it isn't finished yet.

· Gerry Gilmore is professor of experimental philosophy at the Institute of Astronomy, Cambridge University.

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