Ever since Galileo turned his telescope on Jupiter and saw the dance of its orbiting moons, we have become used to the notion that there is more to the universe than meets the eye. Not content with finding new moons, predicting comets or revealing planets, the astronomers of the 20th century radically expanded our horizons, and definitively toppled mankind from its place at the centre of things. First they found we are situated in the suburbs of a galaxy far larger than anyone had ever supposed, and then that this galaxy is surrounded at almost unimaginable distances by almost unfathomably many other galaxies, which are all rushing away from each other at almost unbelievably high speeds as the universe expands. But as the 20th century came to an end it became clear that even this immensity is only a small fraction of the universe that surrounds us. Look up into a clear night sky, and the light which you see is produced by celestial bodies made from a type of matter representing only 4% of the stuff of creation  a figure which gives Richard Panek the title of his pacy account of how astronomers realised new depths to their ignorance.

Panek opens his story in characteristic fashion when a brown-bag lunch in 1965 is interrupted by a telephone call. The Princeton physicist who picks up the phone announces to his colleagues that they've been scooped  a couple of astronomers at a rival institution have discovered the cosmic background radiation that he and his colleagues were planning to look for. For Panek, this faint radiation arriving from all directions is the first experimental confirmation of big bang theory, and the moment at which cosmology made the transition from celestial just-so story to science. It also launched an astronomical revolution as scientists tried to answer the obvious question posed by a theory which posits that the universe began in a super-dense explosion: how will it end?

Astronomers tackled this final question by searching for distant supernovas  massive stars that die in brief explosions as bright as an entire galaxy. Measurements of their brightness and their spectra could determine if the gravitational tug of matter would be strong enough to pull the universe back into a big crunch, or whether it would go on expanding for ever. Panek follows the competition between a team of Stanford particle physicists, which began searching for supernovas in the early 1980s, and a looser alliance of astronomers set up in the early 90s, as they struggle with intergalactic dust, lost data and the weather in pursuit of tiny glints in the vastness of space which are visible for a matter of weeks.

This is a story full of observational conundrums, throwing light on theoretical explanations as small problems provoke wider questions. The puzzles of galactic rotation, where both galaxies and clusters of galaxies seem to be spinning so fast that they ought to be tearing themselves apart, are given a whole chapter, while the standard model of particle physics, which provides a list of possible candidates to hold them together, is given only a paragraph. Panek has clearly got to know the major papers in the field as well as the scientists themselves, quoting from email correspondence and interviews he has conducted to give a rich portrait of modern scientific life. But the lack of images in the book often leaves him performing descriptive somersaults in an attempt to conjure up pictures of colliding galaxies, or diagrams of instrumentation and results which could easily have been included. There's even a moment where scientists at a conference rejoice to have "something to see"  another graph which is not included in The 4% Universe.

Panek's scientists are a brave, dedicated and informal bunch, always only a whisker away from running out of funding, who dare to challenge received wisdom, follow hunches and seem to do most of their best work over beer and pizza. The intense competition, where a speaker at a conference can lament that a graph is "about 45 minutes out of date" following an earlier presentation, finds the group of astronomers  set up along unusually democratic principles in the hierarchical world of modern science out of distaste for its politicking  embroiled in a bitter dispute over priority, as a new standard model of cosmology is forged.

It is an unnerving picture of the world, where precise determinations have been made of quantities which no one fully understands. The major component of the universe, making up 73% of its substance, is "dark energy"  so called because no one has the faintest idea what it really is. Next, with 23%, comes "dark matter"  so called partly because you can't see it with a telescope, even though it seems it must be there to hold the structures of the universe together, but also because there are only hints and suppositions as to what this mysterious substance might be. The remaining 4% is the stuff of you and me, and of the "next Newton", who Panek suggests will be required to unite the physics of the very small with the physics of the very big and shed some light on all this darkness. It is perhaps a sign of the health of modern science that the harbingers of so much doubt have met with such acclaim.