Dichronauts

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Dichronauts is a 2017 hard science fiction novel by Australian author Greg Egan, published by Night Shade Books. The book imagines a universe with two time dimensions: one that governs time’s flow as characters perceive it, and another that shapes spatial perception. To see in all directions, beings form a symbiosis between Walkers (who move) and Siders (who provide vision). In this world, cities migrate to follow the sun, creating a shifting habitable belt.

Plot in brief
- The story follows Seth, a Walker from the city Baharabad, and Theo, a Sider living inside a walker’s skull, as they join an expedition to map safe routes at the edge of the habitable zone.
- They encounter a river near the city Thanton, where Walkers seem to have poisoned Siders. Dialogues about their uneasy symbiosis and concerns about Sleepwalkers drive the tension.
- A vote among the expedition members leads the group to press on rather than return home. Their journey ends with a cliff that hints they may have reached the world’s edge.

Background and ideas
- Dichronauts sits alongside Greg Egan’s Orthogonal series in exploring alternate physics, but it stands alone: it flips the meaning of space and time by changing the metric signature that describes spacetime.
- In this universe, gravity, light, and even the shape of planets behave very differently. Objects can roll uphill in certain orientations, there is a form of negative kinetic energy, and planets can have non-spherical, even hyperbolic shapes with multiple surfaces.
- The book explains these ideas through both narrative and on Greg Egan’s related online materials, including interactive simulations.

Reception
- Critics found the novel extraordinarily strange and ambitious. Publishers Weekly called it “impressively bizarre” and suggested Egan may have out-Eganed himself.
- Kirkus Reviews noted that the world is very odd and hard to visualize, but acknowledged Egan’s talent for inventing strange new universes.
- Locus Magazine described the book as dense and challenging but still full of interesting ideas from Egan.

Publication details
- First edition hardcover, 294 pages
- Publisher: Night Shade Books
- Publication date: 2017
- ISBN: 978-1597808927
- OCLC: 954670201

External notes
- Official website and related readings by Greg Egan are available for readers who want to explore the concepts more deeply.