The novel “The Arrows of Time” by Greg Egan was published for the first time in 2013. It’s the third book in the Orthogonal trilogy and is the sequel of “The Eternal Flame“.

The generation starship Peerless is traveling through space in search of a technology that can save its crew’s homeworld taking advantage of the fact that on the starship time flows differently than the planet. However, after some generations, some people are not interested in working to save a world they have never even seen.

The many scientific and technological advances have also led to profound social changes, not without problems. When an instrument that allows to communicate with the future is created, the reactions are very different. It’s decided to put its use to vote but there are those who want to prevent that possibility by any means.

In the last book of the Orthogonal trilogy, Greg Egan jumps forward in time again, starting it at a key moment of the mission of the Peerless, the mountain turned into a huge starship in the first book. In a story that spans generations, once again the characters change and in many ways the third book is independent from the previous two but you need them to understand the universe it’s set in.

From the first book, Greg Egan started describing the physical laws of the universe in which the Orthogonal trilogy is set, different from those of our universe, through various characters’ scientific discoveries. The author put on line a section of his website that explains the physics of that universe but it’s not like reading the novels. I think it’s best to read the three novels in a rather short time to avoid having to re-study every time at least some of the physics of that universe.

There’s the further complication given by the fact that the protagonists of the trilogy are aliens that belong to a species with an anatomy and a physiology completely different from those of humans. It’s an important element in the course of the trilogy influencing in different ways the plot, particularly concerning medical science advances and their reproduction, a theme that Greg Egan kept on developing in “The Arrows of Time”.

In the Orthogonal trilogy, the story of technical and scientific progress goes hand in hand with that of social changes, typically accompanied by disagreements between groups with different opinions that sometimes lead to violence. In “The Arrows of Time”, the problems start due to the fact that not everyone wants the Peerless to return to their ancestors’ planet and get worse when a way to communicate with the future is discovered.

In that universe time works differently than in our universe and in “The Arrows of Time” This is a central element in the whole plot. One consequence is the possibility of establishing communication between the past and the future. Creating a device to communicate with the future has profound consequences on the passengers of the Peerless and some of them are willing to resort to violence to prevent its use.

The problem of the conflict between free will and a fixed future is explored even if sometimes it’s a little overshadowed by the many scientific discussions and clashes between the factions favorable and contrary to communications with the future. It’s a philosophical problem as well and perhaps Greg Egan is not the most suitable author to develop it from that point of view.

Time’s behavior in that universe is also seen in the expedition to the planet Esilio, an appropriate name as it’s the Italian for exile and the goal is a scientific research but also a survey to see if there’s the opportunity to found a colony there. Again, in addition to the scientific element there’s the relationship among the characters as people with different opinions must work together for several years.

There are several possibilities for the future of the Peerless mission and it’s curious that in “The Arrows of Time” the Council that governs the activities aboard seems quite far away, also compared to the previous book. It seems that its members are politicians attached to power that for some reason keep on being elected. As in many other occasions, the characters are aliens but in many ways are similar to humans.

Thinking about all the themes included in the Orthogonal trilogy and the very long story-arc, the ending is rather abrupt. It really seems one of the cases where the journey is more important than its destination. Aside from that, “The Arrows of Time” seemed to me a satisfactory end to this trilogy.

If you have already read the previous two novels and you liked them, “The Arrows of Time” is a must-read to complete the story. If you have to start the trilogy keep in mind that it’s mostly for hard science fiction fans who can appreciate its strong scientific component.