The jacket for Cixin Liu’s new novel carries a blurb from none other than Barack Obama: “Wildly imaginative, really interesting … The scope of it was immense.” What the publishers rather disingenuously neglect to specify is that this and the other glowing review snippets are not for the present book at all, but for the multi-award-winning, global phenomenon that was his Remembrance of Earth’s Past trilogy, beginning with The Three-Body Problem (first published in English in 2014). Those novels are indeed a monumental and wondrous achievement: a mind-bending hard-sci fi epic peopled by vivid and lovable characters, in which the story just happens to explain why we have the laws of physics we observe.

Admirers of that sensational triptych will find something rather different in The Supernova Era, which Liu actually wrote in 2003, before the first Chinese edition of The Three-Body Problem in 2007. Though it is adorned with the colourful nebulae of space-opera art, it is primarily a work of speculative sociology.

That only becomes clear, though, after a masterful opening sequence detailing the death of a star. Liu is superb at creating drama from technical description (before becoming a writer, he worked as an engineer at a power plant), and he ramps up slowly to the moment of a supernova with exquisite tension. Why should we care about another supernova? Because this one is happening all too close to us: a mere eight light years away, a star that had been hidden from human eyes behind a dust cloud is now exploding.

Eight years later, the radiation arrives at Earth, lighting up the atmosphere and wrecking DNA in all the life forms on the planet. The authorities soon realise that everyone will die in a matter of months, except for children aged 13 and under: they are young enough, it is discovered, that their bodies can repair the DNA damage. In the time remaining, the adults have somehow to train the children in the disciplines required to keep agriculture and technological civilisation going, and select national leaders to take over when they die. The novel focuses on the three 13-year-old Chinese children who are to rule the country, and later on their American counterparts.

Facebook Twitter Pinterest Cixin Liu. Photograph: Imaginechina/REX Shutterstock

What happens when children are left to run the world on their own? It’s no accident that one character mentions William Golding’s Lord of the Flies, but Liu’s patient working out of the thought experiment is weirder and wilder. His children are mostly immature and silly, but also imaginative and utterly brutal. The first months after the adults all die are like a PG-rated 120 Days of Sodom, with anarchic quantities of chocolate and alcohol. The Chinese children design an enormous theme park and a city made of confectionery, while the American children raid armouries and go round shooting at cars.

Eventually such trivial forms of fun, however, get boring. Children like to play, and what are the best toys the adults have left lying around? Guns, and also helicopters and aircraft carriers. So the warming continent of Antarctica is used as the arena for the first Olympic Games of the children’s era, in which the events are bloody and attritional contests that use tanks, mortars and live grenades. It’s like a massively multiplayer Hunger Games that the contestants have dreamed up for themselves.

The novel is written in pseudo-documentary style as though by a much later historian, incorporating transcripts and extracts from memoirs as well as real-time dialogues between the Chinese characters and other members of the international paedocracy. In Joel Martinsen’s translation it proves an effectively ironic technique – a version of it has been used more recently, too, in Jeffrey Lewis’s brilliant novel The 2020 Commission Report on the North Korean Nuclear Attacks Against the United States – and this novel even ends with a Tolstoy-style disquisition on competing ideals of historiography in its imagined future.

The author, in an afterword, invites us to read it allegorically: first, as a fable about how the younger generation now are growing up in a world frankly incomprehensible to their elders; and secondly, as a description of the state of humanity itself, alone and infantile in the universe, with no user manual to guide us. It’s a credit to the power of his imagination that such interpretations do not overpower the vivid and sometimes horrifying imagery of the story. Early on, the narrator remarks, with affectionate condescension towards his ancestors: “Though they knew they were living on but a speck of dust in the cosmos, they had not truly come to accept this fact.” It may be that we never will until it’s too late.

• The Supernova Era is published by Head of Zeus (£18.99). To order a copy go to guardianbookshop.com or call 020-3176 3837. Free UK p&p over £15, online orders only. Phone orders min p&p of £1.99