Sara Walker is not joking. The first lines of her new book Life as nobody knows itshe calls out some well-known intellectuals for not having answered the age-old, fundamental question “What is life?” Subtitled The physics of the origin of life, One of the main themes of the book is a critique of the orthodox view in the natural sciences that life is an “epiphenomenon.” This is the argument often heard in mainstream popular science that life is some kind of illusion. It is nothing special and can be fully explained by atoms and their motions. Walker’s refutation of these arguments is bold, refreshing, and long coming.

I first met Walker at the famous 2018 NASA and Technosignatures meeting, where the space agency convened a group of us to develop new methods for searching for intelligent life beyond Earth. I was deeply impressed by her creativity, her insights, and how much fun she was to talk to. As I dug into her papers, I found a way of looking at life on Earth (and elsewhere in the universe) that changed my thinking on both topics.

In the standard perspective of physics, living systems are completely reducible to the atoms that make them up. If you know the laws that govern these atoms, you’re done. The rest is just details. Proponents of this view will admit that these details are complicated. Nevertheless, they will argue, nothing fundamentally new is needed to explain life. If you had God’s computer, you could in principle predict everything about life from these atoms and their laws.

Walker doesn’t want to hear about it. For her, the crucial difference between life and other kinds of “things” is the role of information.

For Walker and those who share her views (like me), life is the only physical system that Used Information. While it is possible to describe a rock by the information in its crystal structure, the rock doesn’t care. The physics of the rock doesn’t require information consideration, because information isn’t needed to explain the rock’s behavior. Life, however, is a different matter. Life needs information. It perceives it, stores it, copies it, transmits it, and processes it. This insight is Walker’s way of understanding those strange aspects of life, such as its ability to set its own goals and be a “self-creating and self-sustaining” agent.

In the first half of the book, Walker describes her path to this perspective. She tells how her PhD supervisor—none other than my friend, co-conspirator, and co-founder of 13.8 Marcelo Glieser—defined three problems that got her thinking: the origin of matter, the origin of life, and the origin of consciousness. These three problems are at the core of science that truly looks at the big picture, and they haunted Walker throughout her early scientific career. Later, she worked with her postdoctoral mentor, Paul Davies, to find an approach to these big questions that could uncover the real problem. Why did all attempts to reduce life to “nothing but” matter fail? This was the beginning of her informational view of life.

Walker writes: “Paul Davies and I wanted to find out which aspects of life prove too stubborn to reduce to known physical and chemical relationships. (…) What we found, quite bluntly, draws attention to the question: How can information make a difference??”

Next, she does a nice rhetorical exercise where she asks the reader to turn the page. On the next page, there is a single line asking the reader to turn the page again. In this way, she concretely shows how information created in her head can cause something to happen in the physical world (you turn the page). What she wants to show is that life is the means by which information becomes causal, and that this kind of causality can only take place in and through living agents (and perhaps artifacts they create à la AI). Information is fundamentally what makes life so different.

In the second half of the book, Walker explains what she believes follows from this insight. She and her colleagues call this Montage theory. I will cover this constellation of ideas in another post. What is important now is the power of this information-centered view to reinterpret much of what is happening at the frontiers of physics. As Marcelo, Evan Thompson and I wrote in our recent book, The Blind Spot Why science cannot ignore the human experienceTreating living agents as some kind of illusory sideshow of a fictitious “theory of everything” is a fundamental mistake. I expect that there will be many attempts to correct this mistake and make the “liveliness” of life the central question of science. However, Walker’s emphasis on information stands out as a promising and paradigm-breaking way to this goal. This is also why Life as nobody knows it is essential reading.