Episode Summary
Executive Summary: Michael Shermer interviews astrobiologist Sarah Amari Walker about her book "Life as No One Knows It" and her push to redefine life through physics, information, and assembly theory. Walker argues that life is an evolved process of constructing complexity, not a fixed property of matter, and that origins-of-life research needs new theory and experiments to detect life—including alien life—more rigorously.
Main Topics: Defining life beyond textbook biology: Walker criticizes standard definitions like NASA’s "self-sustaining chemical system capable of Darwinian evolution" as too narrow and Earth-centric, arguing they fail to capture the difference between living and nonliving matter. Life as emergent complexity and information: She frames life as an emergent process of evolution that constructs complex objects and stores/propagates information over time, rather than a mystical force or a simple property of atoms. Assembly theory as a new framework: Walker explains assembly theory as a way to quantify how much historical construction and selection an object requires, using assembly index and copy number to distinguish life-generated complexity from abiotic chemistry. Aliens, biosignatures, and scientific explanation: The discussion emphasizes that detecting alien life requires more than anomalies or molecules like oxygen/phosphine; it requires a deeper explanatory theory of what life is and how it forms. Philosophy of science and explanation: Shermer and Walker discuss falsifiability, the role of mechanisms, and why good theories must be hard to vary. They contrast explanatory frameworks in evolution, gravity, and origin-of-life research. Consciousness, free will, and materialism: Walker presents a broadly materialist view in which consciousness, mathematics, and information are physical/collective phenomena, but she is more cautious about consciousness than about life. Scientific biography and path into astrobiology: Walker recounts how physics training, graduate work on homochirality, and mentorship from Marcel Gleiser and Paul Davies led her to origin-of-life research and the development of her current ideas.
Key Arguments: Life should be understood as what evolution can construct, not just as a chemical system that metabolizes or replicates. Traditional life definitions are too narrow because they exclude boundary cases (like viruses) and include nonliving systems (like cars or fire) in inconsistent ways. Information is materially real in the sense that it has causal power, can be copied with meaning, and is central to biological organization. Assembly theory offers a testable way to identify life by measuring the complexity and historical construction of molecules and other objects. High-assembly-index molecules observed in abundance are strong indicators of life because abiotic processes rarely generate such objects repeatedly. Detecting alien life by anomalies alone is insufficient; science needs an explanation of life that can guide search strategies and mission planning. Current origin-of-life models, including simple RNA-first narratives and non-equilibrium statistical physics alone, do not adequately explain the transition from chemistry to living systems. The origin of life likely involves phase transitions and abrupt changes in the space of possible constructions, not just gradual accumulation of a single molecule type. Consciousness, mathematics, and laws of nature should not be treated as fully autonomous platonic entities; they are best understood as physical/collective patterns within our universe. Good explanations are hard to vary, while weak explanations rely on labels or mystery terms instead of mechanisms.
Data Points: Book title: Life as No One Knows It - Walker’s new book discussed throughout the interview. Publication date: August 6 - Shermer says the episode will likely release on the date the book comes out. Assembly index threshold: about 15 - Walker says life-associated complex molecules above this threshold have only been found in life when observed in abundance in Earth chemistry. Lab size: about 15 people - Walker describes her research lab at Arizona State University. Chemical complexity example: 1.5 universes - She says one copy of every structural permutation of taxol would fill about 1.5 universes. Taxol molecular weight: 853 - Used as an example of how enormous chemical space is even for relatively small molecules. Human timescale example: 3.5 billion years - Michael Lachman’s remark, cited by Walker, that he is "3.5 billion years old" because life is a lineage. University/lab affiliation: Arizona State University - Walker is deputy director of the Beyond Center and a professor there. Award mentioned: Stanley L. Miller Early Career Award - Introduced as recognition for her origin-of-life research.
Pivotal Quotes: "Life is not a property of matter." — Sarah Amari Walker: She uses this to argue that life is better understood as an emergent process and a product of evolution rather than a static material property. "We don't know the answer to this question. And so for me, you know, that just really says we should just say we don't know." — Sarah Amari Walker: Her response to the unresolved origin-of-life problem and the need for new ideas and experiments. "The universe is designing itself." — Michael Shermer: Shermer’s summary of Walker’s bottom-up, non-theistic framing of emergent complexity and evolution.
Implications: If Walker’s framework holds, origin-of-life and alien-life research will shift from searching for familiar biomarkers to measuring construction, information, and complexity. That could make life detection more testable, broaden astrobiology, and reshape how scientists think about agency, consciousness, and evolution.