Afterthoughts: The Dark Forest by Liu Cixin

We should all be learning in public

Evaluating the impact of our efforts

Dark Light

The Dark Forest (TDF) is a rare sequel that comfortably eclipses its predecessor. I thoroughly enjoyed The Three Body Problem (TTBP), and so my expectations were tempered for this book. To my surprise, Liu Cixin outdoes himself. I have a much greater appreciation now why he has been elevated into such rarified air. Grim is the word I would use to describe the work, along with bold, expansive, and dark. Like in TTBP, the characters themselves are not the strengths of the work. Luo Ji, Da Shi, Zhang Beihai, Bill Hines, Manuel Rey Diaz, and Frederick Tyler: they all represent different elements of the human response. Each of which are intricate, yet tenderly unravelled from start to finish. It is Liu’s ability to weave these characters’ arcs within the political, scientific, philosophical, and ethical cross-currents that make him, and this, such a compelling read.


The dark forest theory of the universe is something I am still thinking about to this day. It is derived from the two axioms of cosmic sociology proposed by Ye Wenjie:

  1. Survival is the primary need of civilisation
  2. Civilisation continuously grows and expands, but the total matter in the universe remains constant

The first is pretty self-evident, the second, however, requires a little more digging. It rests on three key conjectures:

  1. Barrier to communication
  2. Technological explosion
  3. Detection reversibility

Across potential life forms, communication is naturally going to be difficult. Even us on earth are unable to effectively nor efficiently communicate with another species. The closest might be man’s best friend, dogs, or perhaps our closest relatives, the primates. But even then, neither of those could in any way be considered effective or efficient. What hope is there between two intelligent species that evolved independently light-years away from each other? That is not even considering the time horizons that are involved in sending and receiving potential messages.

In the 5,000 or so years of recorded human history, the level of our technology has exploded in the last 200 years in the industrial revolution. No one can imagine how this technological evolution, or explosion, will continue to grow in the next 1,000 or even 10,000 years. Given the one data point we have for technological progress i.e. us on Earth, technological capability explodes in what are essentially milliseconds on the cosmic timescale. Given the universe is 13.8 billion years old, for a species to achieve our current level of technology, they do not need millions of years, they need less than 10,000 (or 200) years.

The final conjecture says if one civilisation can detect the existence of another in the universe, sooner or later, the second civilisation can also detect the existence of the first. This is primarily due to the inevitable phase of technological explosion that would occur.

Based on these axioms and conjectures, one can deduce a possible shape for cosmic society. It is one that sits at the foundation of Liu’s series:

The universe is a dark forest. Every civilisation is an armed hunter stalking through the trees like a ghost, gently pushing aside branches that block the path and trying to tread without sound. Even breathing is done with care. The hunter has to be careful, because everywhere in the forest are stealthy hunters like him. If he finds other life—another hunter, an angel or a demon, a delicate infant or a tottering old man, a fairy or a demigod—there’s only one thing he can do: open fire and eliminate them. In this forest, hell is other people. An eternal threat that any life that exposes its own existence will be swiftly wiped out. This is the picture of cosmic civilisation. It’s the explanation for the Fermi Paradox.


Haven’t raced through a book that fast since I was 10 reading YA fiction of the action/adventure variety. It spotlights a rather grim theory for Fermi’s paradox, and one for humanity’s response to it. To describe this book as dark would be an understatement, yet it never failed to entertain – a classic page turner that will linger for a long while thereafter.

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