The Second Arrow of Time: Evolution, Complexity and New Laws of Nature Robert M. Hazen and Michael L. Wong WW Norton (2026)
Some ideas begin as radical scientific propositions before becoming familiar concepts for future generations. In The Second Arrow of Time, mineralogist Robert Hazen and planetary scientist Michael Wong argue that their central insight could eventually become part of mainstream science: nature has a built-in tendency to generate complexity and order.
The Second Arrow of Time examines how the Universe moved from simple beginnings to increasingly complex systems. Hazen and Wong argue that science has not yet fully explained this “obvious truth” and call for new principles that can describe evolution across living and non-living systems.
How the story of life and Earth unfolded – together
The authors begin by explaining how the laws of physics enable scientists to predict the behaviour of matter throughout the Universe. Their main focus is the second law of thermodynamics, which states that energy tends to spread out over time and that overall disorder, or entropy, increases.
Consider a snowman on a warm day. Heat weakens the hydrogen bonds that maintain the rigid structure of ice, causing the snow to melt into liquid water. Organic matter undergoes a similar process as its chemical bonds break down and its atoms disperse through the soil, atmosphere and water.
The second law of thermodynamics is often called the “arrow of time” because it gives events a clear direction. Snowmen become puddles, and green leaves eventually turn brown. Hazen and Wong accept this thermodynamic arrow but propose that another process operates alongside it—one that points towards increasing complexity and organisation.
Natural selection beyond biology
Hazen and Wong ask scientists to consider why order repeatedly emerges from relatively simple and random starting conditions. They point to the formation of chemical elements through nuclear fusion, the development of minerals and compounds, and the evolution of intelligent life as examples of nature generating increasingly organised systems.
According to the authors, these organising tendencies are so widespread that “there must be a second arrow of time” explaining “the universal tendency for particular systems to display increases in turn.”
Ice forms a rigid crystalline structure due to hydrogen bonds formed between water molecules.Credit: Getty
This is an intriguing proposition. Just as life on Earth became more complex as it evolved from single-celled organisms to multicellular life, atoms, stars, minerals and other systems may also follow evolutionary pathways of their own.
The authors argue that order can emerge from disorder when three conditions are present: a system must have many possible configurations, it must be capable of producing new forms, and there must be a mechanism for selecting among those forms.
The secret relationship that governs life on Earth
Hazen and Wong use the concept of “functional information” to describe this increase in order. It can be estimated by comparing the number of forms that actually exist with the far larger number of theoretically possible configurations. When only a small fraction of possible forms emerges, functional information—and therefore organisation—rises.
Human language offers one example. Language developed from the many sounds humans can produce, the ability to combine those sounds, and the value of using them to communicate ideas. Across generations, some sounds and combinations became established because they served useful communicative functions.
Attractively written and highly thought-provoking, The Second Arrow of Time is likely to inspire debate among scientists and philosophers. The book’s ideas may themselves undergo an evolutionary process as researchers test, refine and challenge them in the years ahead.
Although Hazen and Wong draw on peer-reviewed research, their proposal is not without weaknesses. The authors acknowledge several counterarguments and concede that they have not yet found “satisfactory solutions” to every objection.
What drives the evolution of complexity?
The most difficult question concerns the relationship between increasing complexity and the second law of thermodynamics. Overall entropy must continue to rise even when local systems become more ordered. Does the emergence of complexity represent only a temporary pattern within an unstoppable flow towards greater disorder?
Answering this question will require scientists to measure functional information in natural systems. That task is technically challenging and raises further questions about how order, complexity and evolution should be defined across different physical and biological systems.
Source: www.nature.com