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Every bookshop in Britain now has a row of books on popular science. Next time you get a chance, take a look at the books booksellers think will sell, and you may be encouraged by the high-minded image they have of their customers. There is little here on the Internet, how motor cars work or how food technology is transforming our eating habits. Instead, the emphasis is on such areas as cosmology, with Paul Davies and John Gribbin to the fore, and on topics like evolution and consciousness, with Stephen Jay Gould still market leader despite heavy competition.

Ask people in the business why the apparently arcane topic of cosmology should be regarded as bestseller material, and they answer you in one word: Hawking. He is credited with creating science as a subject that sells books, and for the revelation that difficult and obscure material need not repel readers. At a time when dumbing down and the 30-second culture are fashionable concerns, this is a significant social phenomenon.

The figures given in this new, illustrated edition of A Brief History of Time support the idea that something changed in the world of publishing when Hawking came along. One copy of the A Brief History has been sold for every 750 people in the world: it has appeared in 40 languages: and it was in the Sunday Times bestseller list for 237 weeks, making it the all-time record-holder. Although Shakespeare and the Bible are excluded from the list, even they probably do not sell well enough week by week to challenge Hawking at his peak. The book remained in hardback for years, selling so well that the publishers avoided producing a paperback. When one finally appeared, the superb slogan for the marketing push was: "It's in paperback, and it's about time."

However, just as people did enjoy sex before the 1960s, so people did read about science before Hawking. Darwin was a substantial bestseller, as was James Jeans in this century. In the modern era, pre-Hawking, writers such as Patrick Moore, Carl Sagan, Isaac Asimov, Nigel Calder and Gould have sold well; and Moore's Sky at Night, now in its 40th year, is the longest-running show on television apart from the news.

But there can be no doubt that A Brief History has changed the way the public sees science. For one thing, it is written by a working scientist who puts himself in the narrative in the first person, such as where he refers to doing his PhD on gravitational collapse, a field pioneered by Roger Penrose. Plenty of other popularisers of science, including two snail specialists - Gould and Steve Jones - have written about their own research, but Hawking has had a vital role in letting the general public know that scientists are comprehensible, if not "normal" people.

The other fact about A Brief History that seems to have entered accepted wisdom is that it is more bought than read, and that it is more likely to be bought as a present for someone else than for one's own delight. Tales abound of copies read only as far as page 30 or thereabouts: and it is certainly true that I have given copies to both of my brothers-in-law but never owned one until the review copy of this version came along.

A Brief History's success was also obtained despite its almost complete lack of the high-quality illustrations that readers have come to expect from books such as Sagan's Cosmos and many other works of popular science. The present volume aims to fill that gap by providing images in addition to the text (which has also been updated). But the publishers have not made the mistake of piling on large numbers of pictures or of making them too large. Used in this way, the illustrations add to the words rather than overwhelm them.

But will this new edition sell well? If you are remotely interested in the subject, you probably already own essentially the same book. Will the new pictures add enough value to persuade you to acquire another copy, or give a second version to someone who got the book from you for Christmas 1991?

If not, you may miss a treat. The pictures include both portraits of scientists and diagrams and other visuals about such matters as the inflationary universe or black holes. As the media fascination with Hawking proves, people find scientists interesting: and anything that helps to unpack dense subjects such as alternative universes, or the concept of spacetime, is welcome. The book is also a far more pleasing and glossy object than the original hardback, while the paperback is a distinctly dowdy affair.

That said, how good is A Brief History? It begins in time-honoured history-of-astronomy mode with Kepler, Copernicus, Galileo, Newton and the rest, although here the story is told with far less subtlety than modern historians of science would regard as appropriate. Thus far, Patrick Moore could have done better, and indeed has done.

Beyond this point, where we enter the world of Einstein rather than Newton, the need for a high-grade guide such as Hawking becomes apparent. This is the territory first charted for the general reader by Steven Weinberg in 1977, in The First Three Minutes. His book has now been overtaken by new research, some of it covered in Weinberg's Dreams of a Final Theory, but it remains a valuable read, probably better than A Brief History.

Where Hawking wins out is in the effortless connections he makes between physics, cosmology and the place of humankind in the cosmos - which turns out to be pretty modest. Hawking is not a fan of the strong anthropic principle, whereby the initial conditions of the universe are thought to have been arranged so as to ensure our ability to complain about higher education funding in 1997 - but he sets out the case for and against it fairly.

The book, especially the new edition with material on wormholes and time travel, is as strong on speculation as on the observable universe. One of its strengths is to show that to a mind such as Hawking's, the two merge into one via mathematics (it contains hardly any equations and other mathematical apparatus; another sign of quality in a work of popular science).

So, can the reader really come out of Brief History with a working knowledge of modern physics and cosmology - and perhaps even an idea of what time is? Here the key is Hawking's chapter, "The arrow of time", which takes the subject on from Einstein's work, in which time was shown to be relative rather than absolute. Hawking's view is that the arrow of time is a fundamental aspect of our expanding universe. In discussing such issues as whether time would run backwards if the universe started to contract, Hawking raises debates and controversies in which he is a participant - and does not hesitate to admit his mistakes.

All in all, The Illustrated A Brief History is worth the asking price. And if you are visiting the South Sandwich Islands, Comet Hale-Bopp, or some other spot the original book has not yet reached, the locals will be very glad of a copy of either version.

Martin Ince is deputy editor, The THES.