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Dichronauts

Greg Egan

3.54 · Rating details · 417 ratings · 79 reviews

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 Se ...more

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Published July 4th 2017 by Night Shade Books

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Mar 18, 2018 Manuel Antão rated it really liked it · review of another edition

Shelves: 2018

If you're into stuff like this, you can read the full review.

Eigen-stuff Applied to Buridan's Ass: “Dichronauts” by Greg Egan

When I read an Egan's book I cannot tackle it on a purely literary level. Egan's fiction makes me think about things I didn't know I wanted to think about. This is another one of those novels with a mind-boggling universe.

Egan's world has far consequences:

The space won't be isotropic any more. Thus, things would behave differen ...more

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Apr 27, 2017 Claudia rated it liked it · review of another edition

Shelves: sci-fi, z-to-a-egan, netgalley

This was one tough book to comprehend. I read all I could find on Greg Egan’ site and some more about differential geometry and I still did not understand how the world imagined by the author works.

Because this is not an action or character driven story, but one in which geometry makes the rules and the reader tries to visualize how this world is constructed. Instead of a 3-dimensional space and 1 dimension of time, we have 2 of each.

After playing with this simulation here, I could imagine a bit how one can move into this ...more

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Nov 04, 2018 Bradley rated it liked it

Shelves: 2018-shelf, sci-fi, worldbuilding-sf

For fans of multiple world-time-lines and especially for fans of Christopher Priest's The Inverted World, welcome to Dichronoauts.

Walking one way brings you to the future, the other, to the past. But space is still space and time is still time. Thanks to the little creature attached to the people here, we've got a cultural/exploratory thing going on that is the spiritual godchild of Priest's classic novel. Just look at the cover to get an idea. That's a picture of the Earth. As in, the Earth, to thes ...more

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Nov 18, 2018 Cathy rated it really liked it · review of another edition

Shelves: read-2018

Symbionts on a planet with a different set of dimensions and shaped as an hyperboloid.

A somewhat human body and a leech-like creature, cohabiting and sharing their life. How do you decide the direction of your life, how do you choose your profession, your partners.... who gives in, who takes precedence, what happens in case of irreconcilable differences? Fascinating.

The book is split in several parts, each part of the book dealing with a distinct section of plot. Part One did a nice job of exp ...more

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Apr 11, 2017 Liviu rated it liked it

Shelves: read_2017, genre-sf, 2017_release_read

finally finished this one and after a great beginning which was very intriguing and another maybe 100 pages that kept me really interested, the book became sort of a slog as the difficulty of reconciling the strangeness of the Dichronauts universe and beings with a sort of human-like behavior started showing more and more and the book became "it sounded a cool idea at the time but it cannot sustain itself beyond an initial introduction" as on the world building side things got stranger and occas ...more

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May 11, 2017 Gary rated it liked it

The world of Greg Egan’s Dichronauts contains two spatial dimensions and two temporal ones. The people of this world are symbiotes, each comprised of a “walker” and a “sider” – siders are parasites who leech nourishment from their walkers; walkers can only see one side of the world on their own and need their siders to see the other.
The sun revolves around the earth in this world, so its people are constantly migrating to stay within its habitable zones. The walker Seth and his sider, Theo, are ...more

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Sep 29, 2017 Tim Hicks rated it liked it

Shelves: science-fiction

If this is your first Greg Egan, just put it down slowly and back away quietly. No one needs to get hurt here. Go find an earlier work as an introduction.

This is hard SF to make Hannu Rajaniemi blush. This is hard SF made of adamantium, or impossibilium. I'm guessing there aren't 200 people in the world who could read this and smile and say, oh, yes, haha, of COURSE it would be like that, wouldn't it?" and maybe ten who could say "ahem, a little error there on page 212 with the rotational forc ...more

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Jan 26, 2018 Tomislav rated it really liked it · review of another edition

Shelves: science-fiction

I read Greg Egan’s new hard-sf novel “Dichronauts” in kindle format. I have previously read and liked a half dozen of his novels, and so I was well prepared that this would be a challenging read.

Dichronauts physics - http://gregegan.net/DICHRONAUTS/00/DP...
Dichronauts world - http://gregegan.net/DICHRONAUTS/01/Wo...

The setting is the outstanding feature in this work, and it is described as a world in a universe with 2 dimensions of space and 2 dimensions of time, rather than the 3 and 1 of our familiar space-time universe. It turns out that is not really an acc I read Greg Egan’s new hard-sf novel “Dichronauts” in kindle format. I have previously read and liked a half dozen of his novels, and so I was well prepared that this would be a challenging read.

Dichronauts physics - http://gregegan.net/DICHRONAUTS/00/DP...
Dichronauts world - http://gregegan.net/DICHRONAUTS/01/Wo...

The setting is the outstanding feature in this work, and it is described as a world in a universe with 2 dimensions of space and 2 dimensions of time, rather than the 3 and 1 of our familiar space-time universe. It turns out that is not really an accurate description, as the geometry is not 2-dimensional in the way of Flatland: A Romance of Many Dimensions. And the characters do not live in 2-dimensional field of time, but along a single linear time line. I think it would be more accurate to say the third spatial dimension is time-like, and able to combine with our regular dimension of time at an arbitrary angle. This leads to all kinds of non-intuitive and weird consequences – such as the surface of a world being hyperboloid rather than spherical. All readers should be aware that there is an Afterword in the book, that gives a brief overview of the physics of the Dichronauts universe and the resultant geometry of their world. But the information at the two links above is much better and includes dynamic illustrations. There is more yet at Greg Egan's website, but I found these two the most useful, and referred to them repeatedly during my reading of the novel.

The narrative never stops to explain the geometry of the Dichronaut world, but it is exposed through events, as the characters travel about, exploring. You see, there is a problem in this world. The hyperboloid world is revolving off axis with regard to the rotation of its hyperboloid sun (see the dynamic illustrations). The areas near and beyond the curve of intersection are uninhabitable, and the observable advance of that curve is driving civilization continually across the world towards a crisis of geometry. The main characters are the symbiotic pair Seth and Theo, who have become surveyors for their city, sent out to search for routes of future migration. The symbiosis is another logical consequence of the world’s geometry, as Seth can only see in one orthogonal direction and Theo senses the other (see the explanation of light cones). During a mission of “conventional” exploration, in which the strange and wonderful surface of the world of the Dichronauts is exposed, the small team of Seth/Theo and a few others discover a flaw of geological scale in their world. The second half of the book then steps the reader up to an even more extreme level of imagination, about which I will not say more here.

The challenge, of course, is understanding the setting. It is a world I had never imagined before reading this novel, but it seems to be entirely a thought experiment. Egan glosses over the physical consequences on particle physics – describing the world and the beings as if they were solid objects, when they would really be arrays of coordinated and intersecting probability fields (yikes!). And I feel there may be dynamic consequences not fully integrated into the way of life of the characters – such as taking advantage of extremely fast travel in diagonal surface directions.
Beyond understanding the setting, it would have been easy to populate the world of Dichronauts with stick-figure characters (metaphorically). There is some of that, as it is not really possible to empathize with beings so alien. But they do have feelings, some of them easily understood, and some of them speculative. After a while, when the characters get beyond the world regions of their own understanding, the adventure takes on a sense of fun reminiscent of Journey to the Center of the Earth.

It would be possible to read this without understanding the setting, just as an adventure in a crazy unpredictable world – but that would miss out on the premise that it is a predictable world. It is an accomplishment just to describe and write a coherent story in this world, and I enjoyed the ride. But it takes work, and that is not for everyone. ...more

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Apr 10, 2017 David Swanson rated it liked it · review of another edition

Fascinating but a bit too clever

As with most novels by Egan, I'm very glad I took the time to read it, and equally as glad that I never have to read it again.

Egan has a knack for introducing us to genuinely alien worlds and viewpoints, and this novel is no different. Introducing exactly how things differ from our viewpoint is possibly a spoiler, but suffice to say that the afterword explains things extremely clearly... if you can grasp the mathematics.

The downside to a ...more

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Sep 30, 2017 Gendou rated it it was amazing

Shelves: science-fiction, hard-science-fiction, fiction

This is another one of Egan's marvelous alternative universes with different physical laws from our own. It's an adventure story following some young denizens of a nomadic civilization. Through the course of their adventure the reader slowly (and with a lot of hard work!) comes to understand the bizarre world they inhabit.

(view spoiler) ...more

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Jul 19, 2017 Pavel Lishin rated it really liked it

Gonna have to brush up on my Dichronaut cosmology, and re-read this one, I think. I'm still pretty unclear how Walkers' hands and fingers work.

There's some interesting parallels here with Peter Watts' Blindsight: The Gang's accusation of what 20th century psychiatry was up to, and Thanton.

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Jul 25, 2017 Craig rated it liked it

This review was originally published at Book Learning.

Who knew geometry could be so confusing?

According to the biography on the inside cover, Greg Egan is a computer programmer. For those who are familiar with his work, if not his biography, that won’t come as a great surprise. Egan writes hard sci-fi, the sort of hard sci-fi that doesn’t take any prisoners and doesn’t bother to go slowly to let stragglers keep up. There is a certain clockwork logic to all his books that makes them feel This review was originally published at Book Learning.

Who knew geometry could be so confusing?

According to the biography on the inside cover, Greg Egan is a computer programmer. For those who are familiar with his work, if not his biography, that won’t come as a great surprise. Egan writes hard sci-fi, the sort of hard sci-fi that doesn’t take any prisoners and doesn’t bother to go slowly to let stragglers keep up. There is a certain clockwork logic to all his books that makes them feel almost digital in a strange sort of way, with plots that roll along with mathematical precision as if guided by some sort of literary computer program.

What I like about Egan though is that between all of the maths and physics, he occasionally manages to slip a punch under your guard and hit you right in the feels. Yes, The Safe Deposit Box, I’m looking at you. Over the years, his work has become more and more esoteric, detailing universes with entirely different physics to our own and looking at the ramifications of what those changes would mean for those living there. Dichronauts is the latest in this sequence, positing a world that’s even more bizarre than that portrayed in his “Orthogonal” series.

You see, in this universe, light can only travel in two dimensions, and the cosmic topology makes the act of rotation seemingly impossible, leaving the intelligent ‘Walkers’ locked into only being able to look east or west, the job of sensing to the north and the sound being taken by the ‘Pingers’, symbiotic creatures who live in the skulls of the Walkers and use a sonar-like ability to determine what lies outside of the light cone. The mathematics of it are, as far as my limited ability can go, impeccable enough, although I have a few problems with the plausibility of the scenario. How life, let alone complex intelligent life, could evolve in such a restrictive environment baffles me. The structure of space in this universe seems to offer no advantage, but imposes a whole lot of limitations on the characters that make even simple tasks an ordeal.

The book takes some time in world-building before it gets to the main “problem,” a seemingly impassable chasm in the path of the protagonists’ migrating city that will block their progress and lead to certain disaster for their society. From there the main characters engage on a Vernean journey to explore the abyss in the hopes of finding a way around or through it. The specifics of the story aren’t as important as Egan’s exploration of how the world’s geometry impacts on the characters though, and there are significant passages of infodump where the protagonists discuss the mathematics of their situation to one another.

So is it a good book? On balance, yes it is, but it’s not Egan’s best work. Part of the issue is that it’s pretty difficult to get your head around how to visualise the story, and this is not helped by Egan’s decision to use cardinal compass points to refer to dimensions in space and time that bear little relation to our own universe. I’m not sure how I would have written this, but using plain old “north” and “south” gives the impression of a relatively simple three-dimensional Cartesian space that just happens to be ‘dark’ in one of those dimensions, an understanding that breaks down completely after events in the second half of the book.

Egan also passes up some interesting opportunities to explore the biology and societal ramifications of the walker/pinger symbiosis. Early on in the book Egan teases what sounds like a fascinating story involving the Elena/Irina pair, and then completely abandons this plot line. For the most part when Egan starts a thread he eventually weaves it into the end, but I was particularly disappointed that we don’t find out anything about how that particular plotline ends.

Those whinges out of the way, Egan has managed to construct yet another strange yet mostly plausible universe and set a story in it that doesn’t sacrifice things like ‘plot’ or ‘story’ in favour of mathematics and world building. This doesn’t rise to the heights of Diaspora, but it’s yet another solid entry in Egan’s impressive body of work. ...more

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Sep 03, 2017 Anna rated it really liked it

Shelves: sf

The book was definitely an interesting read, from the point of "actual hard science fiction" instead of "a mix of romance and humans fighting each other in an unusual setting". If you are into the first type (which not necessarily means completely disdaining the second :D), and willing to invest some mental efforts into imagining the world based on different geometry rules than our own due to having two space-like and two time-like coordinates, and therefore different constraints and consequence ...more

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Aug 19, 2017 Ryan Lackey rated it it was ok

Greg Egan might be my favorite sci-fi author (top-5 for sure), but this is both his worst book to date and a bad book overall. It is built around some completely novel physical geometry and universe dimensionality, poorly explained in the book (to have any hope of understanding, you'll need a guide on Egan's website), but that's fine. The problem is that is really the only positive part of the book; the rest is a stupid/weird morality story about different groups and coexistence (4000/800 had a ...more

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Oct 27, 2019 Quinn Dougherty rated it really liked it

very impressive! i thought it would've been nice as two books-- in one, a story about the physics of an infinite hyperboloid planet (and the edge cases where that model breaks down), and in another, a story about humanoids who rely on slug-oid parasites for more than half of their sensory input. But, for the sheer joy of being able to tell you this book exists, I'm ultimately glad both stories were fused into one.

it's not even that weird, he makes it relatable i swear.

Of course i could spend t ...more

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Dec 17, 2018 Shhhhh Ahhhhh rated it it was amazing

I have mixed feelings about this book. It's a striking, novel concept. Describing the physics of a novel universe where tipping over means stretching out into infinity and dissolution, is necessarily novel. Wrapping my mind around the story happening in that strange space was a new and interesting sensation while reading. It definitely raised the difficulty level for me. Nevertheless, I found the basic, and archetypal, story to be fairly entertaining. In fact, the elements of their world, while ...more

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Aug 01, 2017 Stacey Kondla rated it liked it

Shelves: 2017

I found this to be a challenging read and quite different from the Greg Egan books I have read previously. The math and geometry in this was a bit beyond me, but it was still an entertaining story with an interesting sociological story thread. I wouldn't recommend this as a starter to Greg Egan, but I'm glad I read it and will be interested to read whatever he comes out with next. Without a doubt this was the strangest world with a very strange society and strange life forms.

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Apr 15, 2019 Eric rated it really liked it · review of another edition

Shelves: science-fiction, 2019-books

Wow!! I don't think I will ever fully understand how the physics of these characters and their world works but I found this book to be very readable. It would be hard to recommend to people who are not into Science/Speculative fiction to a fair degree but if people are willing to take a leap into the unknown this is an interesting and mind bending world to experience.
My first Greg Egan read and I will be exploring more of his work.

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Dec 04, 2017 Baal Of rated it liked it · review of another edition

Shelves: canned-soup

Like all of Egan's work, this novel is based on some mind-twisting speculative premises, in this case what would it be like to be in a world with 2 spacial and 2 time dimensions. I found it absolutely necessary to read the supplemental materials on his web site to help with comprehension. From that perspective, this book is good, however the story itself was unfortunately boring, and the characters seemed too human despite the fact they were symbiotic pairs, one of which lived in a hole in the s ...more

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Apr 22, 2017 Guilherme rated it liked it

This really should have been a comic or videogame, or anything with more of a visual component to it. I hadn't even realized it was possible to get myself this mixed up in regard to cardinal directions.

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May 03, 2017 Kam Yung Soh rated it really liked it

Shelves: sf-and-fantasy

Another interesting Hard SF read by Egan. It's not as mind-bending or physics-bending as his "Orthogonal" series but contains intriguing ideas and characters. In contrast to his previous books where the characters slowly learn (and educate the reader about) the physics of their environment, here they are already well versed in the strange (to us) geometry of their universe and its consequences.

In this book, Egan posits a world that has two space dimensions and two time-like dimension ...more

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Jul 11, 2017 S.J. Higbee rated it it was amazing

In order to be better able to visualise this world, my firm advice is to visit Greg Egan’s site at the link:
http://www.gregegan.net/DICHRONAUTS/D...
where you can discover how he came up with this intriguing creation and the inhabitants. Alongside all the maths, the world is also more fully explained before you plunge into this one. Inevitably, I discovered the site after I had completed the book and although I had picked up the gist of what was goi ...more

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May 30, 2019 Lavinia rated it it was amazing

This is mind-strainingly weird sci-fi. No one I have described it to will read it, but I loved almost every minute: it's one of the few books I'd like to reread. The e-book I bought has notes at the end (which I didn't realize until I got there), but I was baffled by the physics of the mundane tasks described in the first chapter. The notes on Egan's website are very helpful and cleared up all the confusion. I think one gets more out of it if they've done the math themselves and internalized the ...more

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Jan 10, 2018 Ariana Mcgee rated it it was ok

I found this book at B&N and purchased it because of the interesting world. I didn't think I would be so disappointed by it. If you like very technical science fiction this book is for you. The author has many sites explaining his view if you would still like to try it. Greg Egan really could have fleshed out his ideas more. I had a very hard time imagining a 2x2 dimensional world. I think the problem was that he was more concerned about the world he created than the intriguing social plot s ...more

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Mar 18, 2018 Mike rated it it was amazing

Egan's universe of two dimensions of time and two of space,his walker/sider symbiotic characters,and his world of constantly migrating ecology is a marveolus creation resplendent with sense of wonder.This book is not for everybody,but anybody looking for a challenging read will enjoy Egan's inventivnes and his briliantly original imagination.Though Dischronauts charactes aren't human, (actualy they can't be human),Egan makes them likeable and even generates symphaty.Seth's sider Theo is particul ...more

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Jun 19, 2017 Mirsha rated it it was ok

Shelves: sci-fi

I wanted to like this story but just found myself unable to really get into it. It takes place in a universe where there is a fundamental difference in physics and it explores what this means, but the books main failing for me is that it does a poor job of explaining how these changes affect the world. I had to consult the web site a couple of times, with it's diagrams and maths, to try and work out what was going on as the book did a poor job of explaining it's rules to me. This left me unable ...more

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Sep 26, 2017 Robmccau rated it it was ok · review of another edition

I generally love Greg Egan's books, but this one just never grabbed me. It felt like it developed too slowly and I never really became interested in the characters or plot. Didn't finish.

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Nov 14, 2017 Marcus rated it really liked it · review of another edition

Shelves: science-fiction, australian-author, aus-sff-novel

Read the Afterword first!

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Dec 21, 2018 Sophie rated it really liked it

I did not find the story especially compelling. It wasn't bad, but I thought it was weaker than Greg Egan's stories usually are. Plot or character development clearly were not the driving purpose behind this novel. What makes this novel interesting is not the story, it's the math.

These two pages from the author's site are essential reading before picking up Dichronauts. The same information was given in an afterword in the ebook I read, but I would have understood and enjoyed the story more ...more

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Aug 10, 2017 Tsana Dolichva rated it really liked it · review of another edition

Dichronauts is a story of exploration and, by some definitions of the word, adventure. The two protagonists are surveyors in a society that puts a high priority in knowing what land lies ahead of it, because it is a constantly migrating society. It has to migrate constantly because it is based on a geometrically very strange world.

There are so many ideas that shape this world into being different from ours, that when I first started reading it seemed like any one of these premises wo Dichronauts is a story of exploration and, by some definitions of the word, adventure. The two protagonists are surveyors in a society that puts a high priority in knowing what land lies ahead of it, because it is a constantly migrating society. It has to migrate constantly because it is based on a geometrically very strange world.

There are so many ideas that shape this world into being different from ours, that when I first started reading it seemed like any one of these premises would have been enough for a perfectly interesting story. However, having finished the book, I can see how all the weirdness, for lack of a better word, is interlinked. No one key premise would have worked rigorously without the other elements holding it together. The geometry of the world requires the migration and begets the alien configuration of the beings we follow in the story. The not-human beings can only see in two directions (forwards and backwards, though they don't refer to them like that) and have a symbiotic relationship with intelligent leech like beings. The Walkers have holes in their heads and the Siders live inside these holes and, through supersonic "pinging" can see sideways and share that information with their Walkers. The Walkers and Siders can also silently communicate, and Siders can speak in the Walker language and also among themselves in their own higher-pitched language that Walkers can't hear. And I've barley scraped the surface of the geometry aspect.

The story follows the investigation of a looming crisis. The river our protagonists' city follows is going to run out as the city continues migrating. Seth and Theo are sent to survey a new region and hopefully find a new river or other means for the city to sustain itself in the future. As they make various discoveries, the situation escalates and they learn more about their world than they bargained for.

This book was a little baffling to read, in a way not foreign to a reader who has read a few Greg Egan books before (ie me). I have a degree in pure maths and one in physics and while some of the geometric ideas were a little familiar to me, I found it difficult to picture some of what happened or predict the effects of some actions. Ultimately, I found the book enjoyable enough if I just went with the flow and didn't overthink it. When I got to the end and read the afterword on geometry (not a spoiler if you want to jump ahead to it), I discovered that I hadn't been thinking of things in quite the right way, which explained some of my confusion. I don't think that knowledge would have helped me all that much if I'd read it earlier, however, since I think a proper representation would be more or less impossible without writing out some equations.

Maths aside, I was also put in mind of Flatland (but without he weird chauvinism), for the exploration of a world with foreign geometrical properties. The main story was more a exploration and discovery yarn, albeit not an exploration of Earth or anything in our universe.

I recommend Dichronauts to fans of Greg Egan and people who are not afraid of unconventional mathematics. Readers who enjoy exploration stories and don't mind not understanding exactly how the physics of the world works should also enjoy this book.

4 / 5 stars

You can read more of my reviews on my blog. ...more

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About Greg Egan

Greg Egan

1,456 followers

Greg Egan specialises in hard science fiction stories with mathematical and quantum ontology themes, including the nature of consciousness. Other themes include genetics, simulated reality, posthumanism, mind transfer, sexuality, artificial intelligence, and the superiority of rational naturalism over religion.

He is a Hugo Award winner (and has been shortlisted for the Hugos three other ti ...more