But nor would the opposite fate come with portents: if a real solution to the Hurtlers was imminent, the moment of salvation would pass without distinction. If such a feat was possible at all then it was due to be achieved any day now, but there would be no signal from the travellers on the Peerless, no manifestation in the sky, no evidence of any kind.

Still, Valeria took the Hurtlers themselves as proof that the travellers’ first goal was attainable: one object really could possess an infinite velocity relative to another. The history of each Hurtler was orthogonal to her own: the tiny rock’s eons of ancient darkness and its fiery passage through the thin gas between the planets all came and went for her in an instant, with nothing but the time lag for the light to reach her prolonging the spectacle. If the Peerless really had been accelerating steadily for the past year, its engines firing without mishap, its relationship to her would soon be the same as the Hurtlers’. Having entered that state, the travellers could maintain their course for as long as they needed, and whether the need was measured in generations or in eras, from her point of view they would live out their lives in the same blink of her eye, regardless.

Valeria stepped away from the telescope and followed the lines of the Hurtlers to their notional vanishing point. Watching from Zeugma, she’d seen the blaze of flaming sunstone as the mountain sped away in exactly this direction. She held up her thumb, blotting out the point in the sky where the Peerless had been heading – blotting out a line that stretched away from her for an immeasurable distance. At the moment of orthogonality, that line would contain the entire history of the travellers from the day they shut off the engines to the day they had reason to return.

In that instant, Yalda would struggle to give the whole endeavour the best foundations she could; in that instant, her time would come and she’d divide or die. In that instant, generations would follow her who had never seen the home world, and knew they never would. But they’d strive to gain the knowledge that their distant cousins needed, because they’d understand that it was the only way their own descendants could thrive. And in that instant, the journey, however long it had continued, would have to reach some kind of turning point. Hard-won triumph or abject failure, the same moment would encompass it all.

Valeria kept her arm stretched out to the sky, humming softly as she mourned the woman who’d helped raise her. But Yalda would leave behind a powerful legacy. Among her successors in that cloistered mountain, free to spend their lives in unhurried rumination, someone would find a way to spare the world from the Hurtlers.

Valeria was done with asking when. With nothing in the sky to prove her right or wrong, she was free to name the moment when the story of those generations finally unfurled, and the fate of the planet was settled in the blink of an eye, behind her thumb.