A great read but very very weird and hard to get your brain around. So it is basically classic greg egan. Will definitely recommend to customers with more abstract and hard scifi leanings.

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 explaining the tensions between the cities competing for resources and the possible societal conflicts, caused by the symbiotic relationships of its inhabitants. And the next parts... well, you‘ll have to find out for yourself.

The tricky part in this book is the planet and its physics. Because of the way it‘s shaped, nothing works as you would expect. I really struggled to picture this world and its inhabitants. I am not sure if it‘s me lacking imagination or if the author did a poor job of explaining it. Or did he do a deliberate job of leaving blanks, to challenge the readers to figure it out by themselves?

It took me over half of the book to even realize that the walkers do not have symmetrical bodies (I think?). I understood that they were shaped differently, with restricted options of movement and a different visual system, but I could not for the life of me picture them for most of the book. Not sure I have the right visual even now, after finishing.

Very, very imginative and pretty much a mystery to me. Without the book blurb I would have been lost in the beginning. Minor degrees in physics, math, astronomy and mechanical engineering might have helped. At one point I started reading up on orbital planes, torque and Euler‘s theorem of rotation.

I got so occupied with trying to understand the physics of this world, that the plot took a backseat until the last few chapters.

This book was hard work! Fascinating stuff and deeply weird. I am docking one star for the sheer incomprehensibility (is that a word?).

I received this free e-copy from the publisher/author via NetGalley, in exchange for an honest review, thank you! Sorry it took me so long....

Well written, but this one just didn't grab me.

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/DICHRONAUTS.html
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 going on, it would have been helpful to have understood more of the complexities of the world and this remarkable indigenous species as I was reading it. However, if this story was simply about an enjoyably weird world and creature with little story or dry-as-dust descriptions bulking up the book – while I would doubtless have something enthusiastic and polite to say about Egan’s extraordinary imagination, I wouldn’t be nearly as excited about this one as I am.

For not only does Egan offer a unique world and alien race – he also provides a cracking adventure story full of tension and excitement right from the start through to the climactic ending. I quickly bonded with Seth and his parasitic companion Theo and enjoyed the tensions and teamwork evident in their linked partnership. What happens if the Walker host has a major quarrel with his Sider? This premise is also explored within the story. I stayed up far later than I should to find out what happens to this embattled species as Seth and Theo struggle to discover a river big enough to support the large city where he was born and bred.

I love this one. Brilliant and inventive, this book reminds me all over again just why I love science fiction so much…
10/10

There's no question Greg Egan is one of the reigning royalty of hard sci-fi. This is as "hard" as it comes - in several senses of the word. This book will be one of the most difficult reads you'll have had recently.

Be prepared: Read two things before you read this book. First, read the appendix, where Egan explains the math, physics & geometry of the world described in this book. Second, go to gregegan.com, read a bit more about the math, and - in particular - play with the interactive simulator he has that illustrates gravitational & geometric forces.

That said, the book is about beings that live in a 4-dimensional universe - just not with the same dimensions we have (x, y, z, and time). The plot line of the book describes a mission undertaken by the main characters to explore more of the world they live on. They must do this exploration because the geometry & physics of the world in which they live puts that world through fairly significant changes, and populations must move to accommodate them. The nature of their wold also causes limits in how each individual can sense, and interact with the world. This causes individuals to typically have a co-existent partner they bond with (literally) for life.

The scout team is forced to go where no person has gone before, and it results in encountering a dramatically different part of the world than they have known, or in which they are prepared to exist. Fortunately, the various life partners *are* more prepared, which permits the story to explore new ideas & opportunities for those individuals.

Spoiler alert: Everything (mostly) works out, though not as you might expect.

That said, I'd have a few more comments.
1) This book is SUPER difficult to understand as you read. Egan uses words like "up", but "up" isn't what you think it is. Consider it instead an expression of a concept that exists for the individuals in their world, but that doesn't represent ANYTHING like your "up". There is plenty of this requirement for suspension of mental-connection in the book - so much so that I found it in the end more frustrating than liberating. I just don't have the mental horsepower Egan has to re-wire my brain in the way required to grok this as I read it. This makes it hard to recommend.

2) This is about as "hard sci-fi" as you can imagine, where "hard" = super amazing, novel, pushing the science / math envelope as far as it can be pushed. This makes it a super-awesome recommendation for your serious sci-fi reading friends.

3) I wished the editor had pushed on Egan a little bit more. I felt the development of the early part of the book was slow, and the resolution at the end was inadequate. The early portion was important to help you get comfortable living in this entirely different world. But not so important as to have spent so much time on it, at the cost of the last 10% of the book (which should have been proportionately longer).

4) God help us all if he writes a sequel that pushes our brains into more difficult extents of this math. My brain will melt.

I usually enjoy Egan's books but this one was not for me.
Still his writing and world building give this title a 3 out of 5.

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.

Sounds insane, doesn’t it? It really does. And is. It is a mind-bending book, not resembling anything else I read so far, the exact definition for sci-fi of ideas. Unfortunately, by not having enough background in math, I can’t say I enjoyed it to the fullest. However, I liked the idea, the relationship between the symbionts, their system of values, the way world is constructed. It’s not the author’s fault that my neurons didn’t live up to the challenge.

But I would recommend this book to all those who welcome a challenge and are open minded, because it is a one of a kind experience.

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 surveyors who scout the migration paths for their home city. Together, they make a discovery, and embark on a journey, that quite literally turns their world upside down.
That journey is not lacking for interesting turns and revelations, though these are only stimulating to the intellect, and to the base desire of the sci-fi reader to explore and map out new frontiers. The physical properties of this world are explored in detail, but its society has no real culture to speak of; they seem to exist only to rationalize their environment, which seems to be all the author is concerned with as well. Characters and relationships are crudely fashioned and bear no emotional fruit to engage the reader.
In other words, if you love geometry as much as Greg Egan does, Dichronauts is your kind of novel. I can’t make a higher recommendation without a more complete experience.