Music, according to its own myth, can pacify a dangerous world; it even has power to raise the dead. A magic flute disarms fanged predators, and Orpheus sings his way into the underworld and resurrects his lost Eurydice. But when John Adams accepted a commission from the New York Philharmonic to compose a tribute to the victims of 11 September, he prudently warned that his score - entitled On the Transmigration of Souls, and performed in the orchestra's first concerts with its new music director, Lorin Maazel - was not guaranteed to be therapeutic. Adams mistrusts psychobabble about the healing process, and knows that a cadence does not necessarily supply what the talk shows call "closure".
He has done his job conscientiously, within the limits prescribed by a compulsory piety: the Philharmonic invited a group of 11 September widows to pass judgement on the score's propriety before performing it. Adams understood the impossibility of dramatising that traumatic day, whose events were already the scenario for a pyrotechnical action movie. On the Transmigration of Souls is therefore reflective, even ruminative. Adams - whose new status as a national supplier of balm and reassurance has pushed him towards a certain grandiosity - likens his little oratorio to Chartres Cathedral. It is, he says, a "memory space", where you sit for half an hour in the company of the dead and experience a sense of "something otherworldly".
That other world is an electronic echo chamber. On a tape, a murmurous city goes about its ordinary business; the only hints of alarm and convulsion are the keening of distant sirens and, even more disturbingly, the clatter of feet in closed stairwells. Invisible voices mumble a litany, naming some of the victims. Then, after a few lulling, cradling orchestral chords, a chorus onstage begins to hum. At first it vocalises rather than uttering words, because grief is inarticulate. Gradually, it manages to pronounce brief elegies, taken from the obituary tributes to office workers and window cleaners and delivery boys published by the New York Times. Its serene composure falters only when it quotes the widow who said she wanted to dig her husband out of the rubble, and insisted that she knew exactly where his body was buried. Meanwhile, a second choir, this one of children, stumbles over the syllables of ano-ther quotation, as if gagging at its irony: "It was a beau-beau-beautiful day."
A disoriented flight attendant, trying to identify the location of her plane moments before the collision, is heard saying: "I see water and buildings." The recorded voice does not register panic; she seems to be already afloat in another existence, like the female hijacker above the brown Virginia hills on Bruce Springsteen's The Rising. The soul's transmigration between states happens painlessly, with no explosive jolts, no sickening concussion as bodies thud on to pavements. After a bell-ringing climax, the chorus begins to cry: "Light, light." That, I suppose, is more tactful than allowing it to mention fire, or the red, viscous vapour into which thousands of people dematerialised. An account of transmigration promises motion, advance, even (as Adams has said) for "those who suffer pain and loss and come away transformed"; the truth about 11 September is that the bereaved mostly feel maimed or incapacitated, not transformed, while the rest of us remain in a condition of numbed, shuddering shock. As if regretting the ambition of his title, Adams stops the music but lets the tape continue, with the noise of a motor that may be a passing car - or is it a plane flying too low?
The concert continued with Beethoven's Ninth Symphony, conducted by Maazel with startling ferocity. Adams claims that his music also espouses Schiller's faith in "our common bond of humanity", rapturously propounded by the chorus in Beethoven's finale. But the staccato thunder of the symphony's first bars made audible the violence that had been banned from On the Transmigration of Souls; and the voice that at last halted the conflict - belonging to the great bass Rene Pape - sounded terrifyingly belligerent.
The choral jubilation came close to what Milan Kundera has called the "collective lyrical delirium" of a society convulsed by a shared ideological fervour. When the pace briefly slackened, the chorus demanded: "Do you fall headlong, millions?" Schiller's words could not help conjuring up the sight of bodies suicidally tumbling from the towers: a detail that was at once brushed out of the photographs and television transmissions. The chorus then asked: "Have you any sense of the Creator, World?", but its stalled, pensive delivery implied that our world, with its randomly destructive physics, has no creator for us to address. A lamenting trumpet on Adams's tape quotes from Charles Ives's The Unanswered Question. But this time, it was Beethoven who asked the uncomfortable, unanswerable questions.
John Adams conducts the LSO in three other works at the Barbican, London EC2 (020 7638 8891), on 20 November