Dichronauts

By: Greg Egan

Narrated by: Paul Boehmer

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.

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 as far as north-northeast is impossible.

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.

©2017 Greg Egan (P)2017 Tantor

A compelling tale with non-optional math

So good. A world with two dimensions of space and two dimensions of time, where all arcs are parabolas so all spheres are parabolic. The edges of the sun scorch the earth, and being directly below the sun is a cone of darkness. The physics of the world are enthralling, and dictate the evolution, culture, and geology of an alien universe where the world is slowly and literally tipping out of balance.

Bold and boring

The Dichronauts universe's unique geometry and constraints made for an interesting thought experiment, but didn't sustain a novel, as very little actually happens. Instead, most of the book is devoted to conveying geometric constraints, which is the primary challenge (along with some cultural and biological dynamics related to the world geometry). Unfortunately, I was only able to visualize maybe 60-70% of the scenarios, leaving some scenes unintelligible even after reading the (frankly required) supplemental material on Egan's website.

Kudos for Egan for making a mostly coherent alternate physics with internally consistent logic, but maybe it would work better as a short story.

It's not an easy book

I loved this book, but if you are not a fan of hard sci-fi, consider whether to go for it. The world is very interesting and it's fascinating how the author could picture life in a completely different space-time, but it takes effort to understand (of course). If you are not afraid to test your imagination however, then enjoy.