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Publisher's Summary

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
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Customer Reviews

Most Helpful
5 out of 5 stars
By Amazon Customer on 05-13-18

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.

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Customer Reviews

Most Helpful
2 out of 5 stars
By Jay on 03-23-18


Generally I find Greg Egan's hard Sci-Fi thought provoking and enlightening, even without knowing all the math behind the universes his stories paint they still stand up as great stories, and there's enough description to paint a picture of the world and it's usually unusual physics in vivid Technicolor, this book was a departure from the norm, the universe the book is predicated on is lacking any explanation within the book and even after studying the physics on his website it was still as clear as mud for a while. While the story thread itself seems to be well put together to a point as an exploration of the universe it inhabits the conclusion is lacking, with little to tie off the dangling plot threads the reader or listener is left to imagine a happily ever after a fairy tale ending to a not very fairy tale plot so far.

Spoilers ahead

Geometry, the book is predicated on a novel geometry with a universe based on 2 time dimensions (hence dichrone from the books title) and 2 space ones but one of the time dimensions isn't explained to be as such and is treated like a space dimension where turning into it is impossible and skews your perspective. The physics does seem to hold as true but there's no exploration of the 2nd time dimension as anything but a novel spacial one. And since it's not explained at all in the text at some point you will go looking on the web for the explanation on Greg's website for why the universe acts the way it does.

Plot, the book's plot is well crafted as an exploration of the world of the protagonist, a shifting axis in effect causing the creatures in the book to migrate with the seasons being the setup for the society and our intrepid dichronauts being some of the people who map the world in advance of the migration. The protagonists are a dual symbiotic entity that rely on one another in a way to provide the vision in their blind dimension(s) but they lack for a good long while a full description that allows you to picture them in the mind's eye. They become surveyors and map the world for the migration and one is clearly a genius because from first principles he figures out, A hot air balloons, B the way the sun orbits the world and the way the world rotates to explain the migration (though without enough detail to let the reader grasp that without the website foot notes) C the edge of the world hypothesis, D more, mostly from first principles. There's moral and personal dilemmas and after getting some real answers about the world and just as the whole thing seemed ready to get resolved the book ends with no conclusion. No epilogue, it just ends. Almost right as the action seems set to start again but with no resolution to the lost companions on the way, no resolution to the thread of what would be done about the migration with the information available. No real resolution of the moral dilemma. The ending being implied to be and everyone lives happily ever after, the people who got lost on the journey made it home and that the protagonist makes it home without further trouble (in spite of a challenging journey ahead) that the moral issue is resolved by something and more questions than answers.

So it just ends with so many unsatisfactory dangling threads I can't really recommend the book at all.

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