The novel “Dichronauts” by Greg Egan was published for the first time in 2017.

Seth and Theo live in a symbiosis that allows them to combine their physical abilities to live and work in their world where there are two spacel and two time dimensions. Seth has mobility and sees forwards and backwards whereas Theo, who lives in Seth’s skull, sees what lies to his left and right. Together they can scout the territory and let others know about the safe routes to travel.

Because of the conformation of the world in which the Seth’s and Theo’s peoples live, they live a nomadic life, periodically moving their cities to keep them in habitable areas. During a survey expedition, the two of them encounter something never seen before, a fissure in the surface of the world so wide that nobody can see how far it gets. The next migration will be blocked unless someone explores a territory different from the rest of the known world.

Greg Egan is one of the most important hard science fiction authors and in various works he used physical laws as foundations, sometimes going so far as to set them in other universes to explore the consequences of different physical laws. “Dichronauts” is set in a universe in which there are two space and two time dimensions with a whole series of consequences that strongly influence its inhabitants’ lives and therefore the plot as well.

The author has created a section of his website in which he describes this universe in detail, with information and illustration. In my opinion going to give us a look is essential to understand if you feel ready to read a novel like that and if so I think it’s very useful to read that section to get help for the novel.

In other works by Greg Egan such as the Orthogonal trilogy, among the important characters there were scientists from an alien civilization who developed physics so the reader could follow their discussions and the attached tables to try to understand that universe. The protagonists of “Dichronauts” don’t have that kind of scientific knowledge and are interested in scouting the territory for very practical purposes so the kind of description of their world is completely different and might not be enough.

To prevent the reader from being completely lost in the fictional universe of “Dichronauts”, Greg Egan tried to provide at least some familiar points of reference. For example, the characters live in cities and there may be rivers near them but in the novel there are also many common terms related to emotions, measures, colors and more. However, those are some kinds of translations of alien concepts into human terms that can be equivalent and understandable to the reader.

This strange world is inhabited by people – where the term must be understood in a broad sense since they’re not humans in the Earth sense – who belong to at least two very different species even if their descriptions are limited. The different physical and sensory skills of the two species led to a symbiosis but in the course of the novel Greg Egan shows that the issue is not so simple. In my opinion this is an element of the novel that could have been developed better but the choice was to provide only rather vague information about the society of that world. There’s a development of important characters that also concerns the relationship between the symbionts but the author focuses in particular on exploration.

Stating that it’s the journey that matter, not the destination is not just a figure of speech in the case of “Dichronauts”. The protagonists move in ways that depend on that universe’s physical laws and after discovering a territory different from everything they knew the description of their exploration becomes even more central.

With “Dichronauts” Greg Egan takes the concept of hard science fiction to the extreme, leaving in the background what doesn’t concern the exploration of that world. If you think you can understand that setting and it intrigues you I recommend reading it.