Science fiction often has challenges of scale at its heart, proposing to take its readers beyond accepted limits of time and distance, leaping the centuries or spanning inconceivable miles of space. Iain Banks's Use of Weapons does not include dates or distances (though his fans construct elaborate chronologies for his novels on websites) but an impression of scale is essential to it. His SF has been called "space opera", and its grand reach across the vasty deep is one reason. His characters take for granted a universe of interstellar travel and extended lifespans.

There are as many worlds out there as a novelist could want. The limitlessness is paradoxical in a novelist whose non-SF novels always have a strong sense of locality. Here most worlds do not even have names. In one episode from the hero Zakalwe's youth, he is sent on a journey that takes a century (made possible by artificially suspended animation). It is in order to fight in a "lo-tech war" on a world that is never named, "flying the frosty vortices of air above the vast white islands that were the colliding tabular icebergs". Nothing else about his mission is explained, but then scale in Use of Weapons is often conveyed by the avoidance of specification. Zakalwe's sister searches for him, following him "on another cold ship, for a century through the intractable calm slowness of real space, to a place where the icebergs swirled round a continental pole, forever calving and crashing and shrinking". The location remains unspecified.

These are chilly places, yet there is something consoling in Banks's transformation of our unimaginably huge universe of lifeless matter and emptiness into a densely populated collection of worlds. Every mission for Zakalwe is a glimpse into one of these worlds: the homosexual priesthood on one planet, who call Zakalwe a messiah; the canyon-dwelling humans of an arid planet where a city is built inside a gash in the planet's crust; the brutalised inhabitants of a place that looks like Highland Scotland but is a slave-driving culture. These mere glimpses are indications of the vast variety of life in Banks's universe.

It is not just space and time: everything is on some bigger scale. In one episode from his earlier life, soon after he has been recruited as a soldier by "the Culture", he finds himself on a spaceship that is over eight kilometres long. How can such a thing exist? The novel makes the stunned Zakalwe ask just this question, to be told by the reassuring but patronising Sma: "It's all done with force fields ... don't try to understand it all too quickly." The scale of things is beyond comprehension.

Yet the novelist still has to focus his story on an individual. In fact, in a universe the fate of which might possibly be manipulated by the Culture – an ultra- advanced galactic civilisation whose agents intervene in the affairs of less enlightened societies to mitigate their errors and brutalities – the concentration on one person's struggles becomes all the more important. The Culture is a substitute for Providence, once the ruling principle of fiction. Its workings are inscrutable – near the end of this novel, Zakalwe is commanded to lose a war that he has been rather brilliantly winning on behalf of the Hegemonarchy, and he rather regretfully complies. As the citadel of the state for which he has fought is stormed, he watches people die who would presumably have lived if he had pursued his successful strategy. "He saw burning people, heard the screams, smelled the roasting flesh. He shook his head." But the Culture knows best.

The beneficent power of this civilisation makes human beings spectators of their own endeavours – fatalists all. It has been noted that artificial intelligences in Banks's novels often possess a quirkiness denied to the human beings. In Use of Weapons, the serenely knowing Sma, an agent of the Culture, is accompanied by a drone called Skaffen Amtishaw which (or is it who?) has a diverting line in chirpy quips and satritical comments on human inconsistency.

The scale of the universe that Banks imagines dwarfs human endeavours. "Everybody is lonely," Zakalwe's sister tells him. Much science fiction asks, as this novel does, what is the point of human effort? Some of Banks's characters are rueful commentators on this inclination. A man cleaning tables in a restaurant on a spaceship asks our hero whether he thinks such a task "does not really signify on the cosmic scale of events". If it does not, then, he asks, what does? "People die; stars die; universes die." So, engagingly, there is plenty of room to recognise what makes Zakalwe laugh, "the sharing of time and place between the grand and the petty, the magnificently vast and the shoddily absurd".

• John Mullan is professor of English at University College London.