For literary agent Pat Kavanagh, Julian Barnes's wife of almost 30 years, it took 37 days from diagnosis to death.

Nobody could fail to be shocked by the brutal speed of her demise, nor to ask, what if that happened to me, or to us? Kavanagh died in 2008, since when Barnes has written his Man Booker Prize-winning novel, The Sense Of An Ending, in which grief, loss, suicide and the value of a life were central concerns. But, until now, with the exception of an essay called Regulating Loss, he has been silent on the subject of his bereavement.

Levels Of Life breaks that omerta in a typically Barnesian, one could also say British, manner. To call it oblique would suggest a directness you won't find in its pages. Head-on tactics would not suit a writer of Barnes's allusive, elliptical, unemotionally contemplative style. Instead, he sidles up to his subject like an athlete making repeated attempts at the high jump, raising the bar a notch each time.

If this sounds like a criticism, it is not. One of the remarkable things about Levels Of Life is that, when setting himself perhaps the greatest challenge a writer can face – of finding words for something so painful and private as to be virtually inexpressible – Barnes soars over the bar without making it tremble. When, midway through this work, he finally addresses his wife's death, he writes with aphoristic simplicity and a calm profundity, without ever sounding self-pitying, maudlin or trite. In time these passages may come to be viewed as the hardest test and finest vindication of his literary powers.

The idea of Barnes becoming airborne is prompted by the scaffolding he builds around his subject, which is about the early pioneers of flight. Beginning with brief descriptions of intrepid balloonists, who risked their lives to see the world from a different perspective, he links the exploits of a French photographer, Felix Tournachon, who was the first to think of taking a camera into the air, with the essence of a love affair: "You put together two people who have not been put together before; and sometimes the world is changed, sometimes not. They may crash and burn, or burn and crash. But sometimes, something new is made, and then the world is changed. Together, in that first exultation, that first roaring sense of uplift, they are greater than their two separate selves. Together, they see further, and more clearly."

Initially, his analogy between flight and love, descent and death, feels contrived, a procrustean bed for a meditation on grief, as when, for instance, he reflects: "So why do we constantly aspire to love? Because love is the meeting point of truth and magic. Truth, as in photography; magic, as in ballooning."

For me, however, that is the only instance when Barnes's sure-footedness falters, when the novelist's compulsion to draw on images and analogies that embellish the facts is a distraction rather than an aid. Thereafter, he does not put a foot wrong. In fact, as he takes the reader deeper into his confidence, there is a most unusual sense of unselfconscious honesty, of baring his soul as mercilessly as the sun bleaches bones.

All who have suffered the death of someone close will recognise his feeling that "what is taken away is greater than the sum of what was there. This may not be mathematically possible; but it is emotionally possible". Evoking the terrifying, disorientating sense of entering uncharted territory, he likens bereavement to having your life "mapped by a new cartography. You seem to be taking your bearings from one of those seventeenth-century maps which feature the Desert of Loss, the (windless) Lake of Indifference, the (dried-up) River of Desolation, the Bog of Self-Pity, and the (subterranean) Caverns of Memory".

He also confirms what most of us suspect: how inadequately friends, acquaintances and family of the bereaved handle their loss. We are all probably guilty at some time of the paralysis that overcomes the bystander who does not know the right thing to say, and therefore often says the wrong thing. Of course, being in the company of a person as sensitive to words and their nuances as Barnes may provoke even greater anxiety and verbal clodhopping.

Discussing the despair he has endured, and the ongoing agony, he admits he considered suicide until he realised that, in killing himself, he would be destroying his memories of his wife – "I was her principal rememberer" – and this now makes it less likely, though not impossible still.

Levels Of Life is at times unbearably sad, but it is also exquisite: a paean of love, and on love, and a book unexpectedly full of life, even when the woman at its core has departed, taking part of him with her. "The fact that someone is dead," he concludes, "may mean that they are not alive, but doesn't mean that they do not exist." By the same token, a book such as this is also inanimate, yet it breathes as surely as, and perhaps for longer than, anything with a pulse.

Levels Of Life

Julian Barnes

Jonathan Cape, £10.99