BOOK REVIEW / When is a stone not a stone?: 'Virtual Worlds' - Benjamin Woolley: Blackwell, 16.95

AMONG Dr Johnson's many famous, no-nonsense ripostes was his refutation of Bishop Berkeley's proposed non-existence of the material world. When Boswell remarked that Berkeley might be wrong, but was impossible to refute, Johnson kicked a large stone. 'I refute it thus,' he claimed, referring to the pain in his toe. Today, given the latest virtual reality technology, Johnson could not be so sure, either of the stone or of his own pain. The questions that run through Benjamin Woolley's excellent book about virtual reality - how real is reality? is it, after all, just an illusion? - will give sleepless nights to those who think Bishop Berkeley safe in his philosophical grave.

'Virtual reality' is the technology that links human perception to a computer-generated, all-embracing, 'felt' image of an artificial reality. The virtual reality subject wears a set of paraphernalia - computer screens before his eyes, 'effectors' covering his body - that simulate a 'real' experience in every detail. He finds himself thrust bodily (or so he feels) into an artificial world, seeing its sights, feeling his own supposed interaction with simulated objects.

The promoters of virtual reality spare no adjectives in singing its praises and potential. 'We are on the brink,' claims writer Howard Rheingold, 'of creating any experience we desire.' Speaking of a recent conference on the subject, the Sixties drug guru Timothy Leary described it as 'one of the most important meetings ever held by human beings'.

Benjamin Woolley is not so sure. Behind all the hype he sees more PR hype. 'When I first donned a virtual reality rig, the last thing I thought of was reality . . . Nevertheless I found it exciting - not intuitively, but intellectually.'

Part of Woolley's intellectual excitement comes from seeing important parallels between the new virtual reality technology and a whole host of other assaults on our sense of reality: the food manufacturers who make it possible for us to eat fat without getting fat, the quantum physicists who tell us reality might not be there until we look at it, the post-modern philosophers who tell us reality is a media construct, and the generals whose high-tech wars are indistinguishable from games in a video arcade - all, claims Woolley, are merchants of unreality.

Woolley has refreshing qualms about all this, and he denies 'the gloomy post-modernists and the bullshitting virtual realists' their victory. Reality, he argues, is not just a construct or a symbol: there is a difference between a simulated stone and a real stone, and, what's more, most of us know it. 'Few people find it the slightest bit odd to think the tree continues when there's no one about in the quad.'

This tour through the simulated, the hyper and the artificial is fascinating and thought-provoking. It raises important questions about a great deal of the nonsense being talked by certain philosophers and computer enthusiasts. It is also a very good read.