THE IDEA'S THE THING : 'Copenhagen' & 'The Real Thing'.

Science has escaped from its ghetto, at least here in Manhattan, where laboratory-minted ideas and images are gaining ever wider currency. The theater scene, in particular, has been awash in theorems. Off Broadway, no fewer than three new dramas about mathematics opened in April and May, while the ambitious Ensemble Studio Theater was wheeling through its second season devoted to drama about science. On Broadway, audiences were flocking to Michael Frayn's Copenhagen, about the German physicist Werner Heisenberg and his "uncertainty principle."

Heisenberg (1901-76) is not exactly a newcomer to the footlights, or to culture in general. Modern writers have been fascinated with the uncertainty principle, which states, roughly, that at quantum level (that is, where things get really, really small), you can know either the position or the velocity of a particle, but not both. Heisenberg's principle and related quantum truths also imply that by observing a particle, you interfere with it. "The act of observing determines the reality," as Tom Stoppard explained in Hapgood, his 1988 spoof about spies and quantum mechanics.

Stoppard and other authors, including Thomas Pynchon, have mined quantum physics for metaphorical resonance, sometimes just in passing. Chicago-based playwright Penny Penniston recently produced now then again, a play touching on some of the same issues as Copenhagen. The British journal New Theatre Quarterly has even run a series of articles discussing the theatricality of the uncertainty principle and corollary axioms.

To the thoughtful person, after all, quantum mechanics seems to provide a welcome alternative to more deterministic science. In the clockwork universe outlined by Newton and his followers, one can (theoretically) calculate, and hence predict, everything. Much modern biology seems to rule out free will, while some biomedical research demonstrates (it may appear) that our ideas and feelings are chemically preprogrammed. The work of Heisenberg and colleagues like Niels Bohr, by contrast, seems to argue for choice--for the mystery of things. Moreover, by attributing an uncanny meaning to human perception, quantum physics reassures us of our own importance. "We put man back at the center of the universe," Heisenberg boasts in Copenhagen.

In Frayn's no-nonsense drama of ideas, such lines volley back and forth with all the subtlety of an artillery barrage--though, to be fair, the narrative premise hardly invites casual chat. Heisenberg (the ever-imposing Michael Cumpsty), Bohr (Philip Bosco), and Bohr's wife Margrethe (Blair Brown) are supposedly meeting after death to hash out the secrets of the past--in particular, to pin down exactly what happened in 1941 when Heisenberg, then a prominent scientist in Nazi Germany, visited Bohr in occupied Denmark. Controversy has swirled around this historical episode ever since. Was Heisenberg, as he later claimed, trying to rally Bohr and other physicists to boycott A-bomb development on moral grounds? Bohr, who fled Denmark in 1943 and eventually worked at Los Alamos, asserted, on the contrary, that his former protege had been fishing for information to aid the German cause. Subsequent research into the Nazi bomb-building project, vastly inferior to its Allied counterpart, has generated still more questions. Did Heisenberg make a series of scientific blunders? Or did he deliberately steer research in the wrong direction?

Copenhagen wrests these possibilities, and their philosophical implications, into a maze of metaphysics. Over the course of two hours, Frayn's characters re-enact variations on the 1941 episode, while the script draws innumerable parallels to the uncertainty principle. Hard facts vanish into the haze of memory--Bohr's and Heisenberg's recollections do not agree--so there's no certitude there. Moral choices seem ambiguous--Heisenberg is torn between patriotism and broader compassion for the human race. And the human character proves as elusive as any quantum particle: the reserved Margrethe, who observes the two men with near-scientific attentiveness, cannot tell whether the German scientist is a friend or a traitor. And he may not know himself--no human being, Copenhagen suggests, can be sure of his or her own motives.

Michael Blakemore's production offers few distractions to this intellectual tug-of-war. The three actors turn in faultless performances, managing to suggest, through voice and sheer presence, both intellectual rigor and determination to battle existential terror. But they spend most of the play standing ramrod straight, gazing at each other across a wooden arena whose simplicity suggests a laboratory's sterility. Startlingly, around a dozen audience members are actually seated at the rear of the stage, looking down on the action from a ledge in the wooden backdrop; the arrangement might allude--yet again--to quantum physics, emphasizing the eerie significance of observing.

Observing Copenhagen itself may thrill well-rested viewers with academic hankerings and excellent powers of concentration, but the play's relentless cerebral forays can also be frustrating. Frayn treats his play like a kind of theatrical subcompact, getting maximum mileage from the uncertainty principle while the story dwindles in the rear-view mirror. The imbalance becomes all the more obvious if one compares Frayn's work with another idea-heavy drama playing a few blocks away: Tom Stoppard's The Real Thing, last seen on Broadway in 1984.

In Stoppard's captivating study of love, thought melds seamlessly with narrative and character development. When the successful playwright Henry (Stephen Dillane) rants about writing ("Words...[are] innocent, neutral, precise...but when they get their corners knocked off, they're no good any more"), for example, his ideas flesh out his personality, and, by explaining the alienation of his dimwitted actress wife, Annie (Jennifer Ehle), pave the way for future plot twists. The Real Thing is Stoppard at his best, and this marvelous revival, which features splendid performances by Nigel Lindsay and Sarah Woodward, as well as Ehle and the brilliant Dillane, pays the script full tribute. Directed by David Leveaux, the production reminds you just how scintillating a drama of ideas can be.

Stoppard's scripts sparkle because he sports with ideas. Even when the thought is dizzyingly complex (Hapgood) or existentially terrifying (Rosencrantz and Guildenstern Are Dead), the scenes that contain it have a disarming game-like spirit. In comparison, a work like Copenhagen, firing off its scientific references so intently, seems formidable and strained.

Plays-of-ideas that, like Stoppard's creations, really play, operate under a sort of aesthetic uncertainty principle--a willingness to entertain a large number of diverse, and sometimes contradictory concepts, without clinging to any one too long. Such an open-minded approach recalls Keats's 1817 theory of negative capability--"when man is capable of being in uncertainties, mysteries, doubts, without any irritable reaching after fact and reason." Quantum physics, on the other hand, allows modern writers to flirt with this attractive state of being, without actually committing themselves to it. With Heisenberg around, you can champion uncertainty and mystery, then blame it all on science.