by Greg Egan


Five steps forward
Three steps right
Are four steps off the path
But keep you safe in sight

Three steps forward
Five steps right
Are four steps into Sider Land
Out of the light

— Children’s rhyme

Welcome to the strangest world in science fiction

Seth is a surveyor, along with his friend Theo, a leech-like creature running through his skull who tells Seth what lies to his left and right. Theo, in turn, relies on Seth for mobility, and for ordinary vision looking forwards and backwards. Like everyone else in their world, they are symbionts, depending on each other to survive.

In the universe containing Seth’s world, light cannot travel in all directions: there is a “dark cone” to the north and south. Seth can only face to the east (or the west, if he tips his head backwards). If he starts to turn to the north or south, his body stretches out across the landscape, and to rotate to face north-east is every bit as impossible as accelerating to the speed of light.

Every living thing in Seth’s world is in a state of perpetual migration as they follow the sun’s shifting orbit and the narrow habitable zone it creates. Cities are being constantly disassembled at one edge and rebuilt at the other, with surveyors mapping safe routes ahead.

But when Seth and Theo join an expedition to the edge of the habitable zone, they discover a terrifying threat: a fissure in the surface of the world, so deep and wide that no one can perceive its limits. As the habitable zone continues to move, the migration will soon be blocked by this unbridgeable void, and the expedition has only one option to save its city from annihilation: descend into the unknown.

Publication history

Information and illustrations

Rotating square in Dichronauts space

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Dichronauts / created Wednesday, 11 May 2016 / revised Sunday, 11 December 2016
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