Sara Imari Walker

Physicist and astrobiologist Sara Imari Walker proposes a new paradigm for using physics to deepen our understanding of what we recognize as life. Assembly theory is a framework that uses the physics of molecular complexity to open a new path to identify where the threshold lies for life to arise from non-life, drawing in insights from new discoveries on the nature of historical contingency and time itself. 

Prior frameworks in both physics and biology have failed to explain life as a general phenomenon. While the Darwinian theory of evolution via natural selection governs much of the development of complex life on our planet, and our contemporary understanding of physics has deepened our understanding of what could possibly exist under its laws, neither system can fully explain how life can originate, nor what forms of life are more likely to exist than others.

Assembly theory is an informational theory of life: it fundamentally holds that life requires information to specify its existence — that objects complex enough to require a many-step, informationally-driven process of assembly are evidence of life, even if the forms they take do not necessarily resemble life as we know it.  

About Sara Imari Walker

Sara Imari Walker is the deputy director of the Beyond Center for Fundamental Concepts in Science and professor at Arizona State University, a fellow of the Berggruen Institute, and an external faculty member at the Santa Fe Institute. She leads one of the largest international theory groups in origins of life and astrobiology, working to understand the evolution of life on our planet and in the universe. With a background in theoretical physics, Walker uses an interdisciplinary set of approaches to explore the problems of the origin and definition of life. Walker co-founded the astrobiology social network SAGANet, is on the board of directors for Blue Marble Space, and is author of Life As No One Knows It: The Physics of Life's Emergence.

Why This Talk Matters Now

Walker’s work as an astrobiologist is all about anticipating the alien uncertainties hidden under the regular patterns of life on Earth. Assembly theory allows us to go beyond these patterns, expanding our imagination of what life could possibly be. As our technology develops further and debates rage about artificial intelligence as a potential form of life, a foundational, physics-driven approach is needed to tease out answers to these deep questions.

Key to Walker’s conception of life is the explanatory power of historical contingency and repeatability. Shearing away from purely probabilistic theories that find that complex forms can emerge randomly into existence, assembly theory holds that historical context and the passage of time matter deeply for the formation of the complex objects that it considers life. Assembly theory builds on prior work on complexity science done at institutions like the Santa Fe Institute, as well as David Deutsch and Chiara Marletto’s work on the Constructor Theory of physics.

Connecting to Long Now

Astrobiology as a discipline has long been of interest to Long Now and long-term thinking more broadly. As a theoretical discipline straddling physics, chemistry, and biology, astrobiology represents an attempt to go beyond the conventional bounds of those fields and take a longer view, leaving aside the assumptions of our present context. In 02017, astrobiologist David Grinspoon gave a Long Now Talk on Earth in Human Hands.

This talk will be hosted by Benjamin Bratton, Director of the Antikythera program at the Berggruen Institute. Watch Benjamin's January 02025 talk, A Philosophy of Planetary Computation.