THEATRE / More than the sum of its parts: Paul Taylor on Tom Stoppard's Arcadia at the National

A COUPLE of years back, Louise Page wrote a play called Adam Was A Gardener, that shuttled back and forth between the present and the early-19th century. It used changing fashions in landscape gardening - from the modified classical vistas of Capability Brown to the new picturesque Gothic style, replete with false ruins and optional live-in hermit - as a metaphor for broader emotional and cultural divisions. In Arcadia (his first full-length stage play for five years), Tom Stoppard gets up to strikingly similar tricks, only - as you might imagine - things don't remain anything like as simple.

Undaunted by the comparative failure of Hapgood, his last theatrical venture, which brought spy pastiche and quantum physics into stubbornly sterile union, Stoppard once again strives to give scientific theory dramatic life and make it part of the play's imaginative pulse and its thematic patterns. Arcadia's concern with the links between the regular and irregular on the aesthetic / social plane finds its scientific counterpart in the mathematical endeavours of two of its key characters.

In the 19th-century scenes, we see Thomasina Coverly, a brilliant adolescent beautifully played by Emma Fielding, as she anticipates modern discoveries about iterated algorithms, the simple mathematical equations that can generate behaviour at once unpredictable and not random. Working from equations outwards, Thomasina hopes to find the geometry of irregular forms. Without a computer, this would have taken her several lifetimes, we're notified by Val (excellent Samuel West), her opposite number in the present-day scenes, who, better equipped, is working in the other direction.

As Val wittily puts it, the second law of thermodynamics (also foreseen by Thomasina) means roughly that 'We're all going to end up at room temperature'. You could be forgiven for thinking that a play full of maths would also produce a fairly steady state of torpidity. What is impressive about Arcadia, though, is the haunting mix of playfulness and poignancy to which, thanks to the author's skills and Trevor Nunn's fine production, the ideas constantly give rise.

Crucial to this effect is the structure. At its simplest, the play is a story of literary detection in which a pair of present-day sleuths, Hannah (Felicity Kendal), a no-nonsense popular historian of classical temperament, and Bernard Nightingale (Bill Nighy), an ambitious, vulgar, far-from-rigorous don of Romantic kidney - lock antlers over Nightingale's theory about the house's unsung place in English letters. While staying at Sidley Park in 1809, he maintains, Lord Byron first cuckolded and then killed in a duel a minor versifier and so was forced to flee the country. Set in the same large room of this Derbyshire country house, the action keeps shifting between then and now so that the audience can enjoy, from a position of superior awareness, the contemporary misinterpretations of the past and its evidence. Having seen Thomasina, as a joke, scrawl a picture of a hermit on to the landscape gardener's sketch of the projected hermitage, we derive a certain smug delight from watching Hannah present this as the only extant likeness of the actual Sidley hermit, the figure who is to be her peg for a study of the nervous breakdown of the Romantic Imagination.

The play is often very funny, but the easy superiority of the structural gags would pall if, alongside this comic demonstration of the past's irrecoverability, Stoppard didn't also give you a wistful sense that the back- and-forth motion is art's attempt to belie the bleak conclusion to which Thomasina's science eventually leads: that all equations are not reversible as in the 'timeless' Newtonian universe and that time moves in only one direction. So when the past and present merge in the dream-like final sequence, it feels like the temporal counterpart to the play's artful blurring of a whole set of distinctions and antitheses.

The play shows how evidence, left partly as a harmless prank, can drive the people who find it mad. This may have been the fate of Thomasina's tutor (sensitively played by Rufus Sewell). Before her premature death, she had granted him a glimpse of a universe consuming itself and he seems to have declined into a career as Sidley's mad hermit, though Stoppard leaves a frisson of mystery. But in its very form, Arcadia lends support to the tutor's earlier optimism about man's endless capacity for self-renewal: 'Mathematical discoveries glimpsed and lost to view will have their time again.' To the idea of entropy, this entertaining and intriguing play puts up a pocket of imaginative resistance.

'Arcadia' continues at the National Theatre, London SE1 (071-928 2252).

(Photograph omitted)