June 13, 2024 • 3hr 1min
#433 – Sara Walker: Physics of Life, Time, Complexity, and Aliens
Lex Fridman Podcast
Key Takeaways
- Sarah Walker argues that life is not just about individual organisms, but is a planetary-scale phenomenon that emerges through causal structures built up over billions of years
- She proposes that consciousness and intelligence are deeply connected to the nature of life itself, and may not be separate phenomena
- Walker believes the origin of life is an ongoing process that continues today through the development of technology and complex systems
- She suggests that our universe may be "small" in space but "large" in time, with living things being some of the largest structures when viewed across their causal history
- Assembly theory aims to measure the boundary between objects that can arise through random processes vs those that require selection and evolution
- Walker speculates there may be a "great perceptual filter" that makes it difficult for complex civilizations to detect each other across cosmic distances
- She argues that computation and mathematics are products of life, not fundamental aspects of the universe
- Walker proposes that free will emerges from our ability to select possible futures based on our deep causal structure
Introduction
Sarah Walker is an astrobiologist and theoretical physicist interested in the origin of life and discovering alien life. She has written a new book titled "Life as No One Knows It: The Physics of Life's Emergence." In this wide-ranging conversation with Lex Fridman, Walker discusses her unique perspectives on the nature of life, consciousness, intelligence, and the structure of the universe itself. She challenges many conventional views and proposes new ways of thinking about some of the deepest questions in science and philosophy.
Topics Discussed
Defining Life (10:40)
Walker argues that traditional definitions of life are inadequate and often break down when examining edge cases. She proposes thinking of life not as individual organisms, but as a planetary-scale phenomenon:
- Life is the process of how information structures matter over time and space
- An example is what emerges on a planet and yields an open-ended cascade of generation of structure and increasing complexity
- Individuals are just particular instances of lineages structured across time
She suggests this broader view helps explain phenomena that don't fit neatly into typical definitions of life, like language or mathematics. Walker states: "I think language is alive, or at least life...I think memes are [alive]."
Time and Space (31:18)
Walker proposes a radical reconceptualization of how we think about the size and structure of living things:
- Living objects are some of the largest structures in the universe, but in time rather than space
- The universe is far larger in time than in space
- Earth's biosphere may be one of the biggest objects in the universe when viewed across its full causal history
She argues this perspective helps explain phenomena like consciousness: "The reason that my conscious experience is not the same as yours is because we're separated in time. The fact that I have a conscious experience is because I'm an object that's super deep in time."
Technosphere (42:00)
Walker discusses the concept of the "technosphere" - the global integration of life and technology on Earth:
- May be the largest object in time in the known universe
- Represents the current boundary of how far life on Earth has pushed into what the universe can generate
- Not separate from biological life, but deeply integrated with it
She argues we need to think of technology as part of life's ongoing evolution, not something separate or opposed to it.
Theory of Everything (46:25)
Walker critiques the notion of a "theory of everything" in physics:
- A true theory of everything would need to be recursive and explain itself
- Current physics theories are not recursive
- She doesn't believe reality has a "ground" or that there's a theory of everything
- Better, more explanatory theories are possible, but not a final, all-encompassing theory
Walker argues the frontier in modern physics lies in studying problems of life and intelligence, not in high-energy particle physics or quantum gravity.
Origin of Life (55:06)
Walker proposes a new way of thinking about the origin of life:
- A boundary that can only be crossed when a structure can reinforce its own existence
- Requires maintaining existence against randomness in chemistry and quantum world
- Involves a transition where objects can't exist unless they have selection and history embedded in them
- May be an abrupt rather than gradual transition
She argues the origin of life is an ongoing process that continues today, not just a one-time event in Earth's past.
Assembly Theory (1:16:44)
Walker explains the core ideas behind assembly theory:
- Aims to measure the boundary between objects that can arise through random processes vs those requiring selection
- Uses two key observables: copy number and minimal number of recursive steps to create an object
- For organic chemistry, the boundary appears to be around 15 assembly steps
- Objects beyond this threshold are only observed in living systems
She suggests this approach could help quantify the origin of life as a phase transition.
Aliens (1:32:58)
Walker discusses the challenges of detecting alien life:
- Proposes the idea of a "great perceptual filter" making it difficult for complex civilizations to detect each other
- Suggests advanced civilizations may "virtualize" themselves, becoming difficult to detect
- Argues solving the origin of life is deeply coupled with discovering alien life
She speculates: "The first contact with alien life will actually be in an origin of life experiment."
Great Perceptual Filter (1:44:48)
Walker elaborates on her idea of a "great perceptual filter":
- As civilizations become more complex, it may become harder to perceive other complex systems
- Draws analogy to how humans didn't perceive microbes for most of history despite their ubiquity
- Suggests advanced civilizations may become so "deep" in time that they struggle to interact with external reality
This concept offers a potential explanation for the Fermi paradox - why we don't see evidence of alien civilizations despite the apparent likelihood of their existence.
Fashion (1:48:45)
Walker discusses her interest in fashion as an intellectual pursuit:
- Sees it as a way to explore the combinatorial complexity of human aesthetics
- Views fashion as the fastest-moving part of human culture
- Uses fashion as a way to bridge deep structure of physics with dynamic human expression
She argues that how we present ourselves aesthetically carries important social and functional implications often overlooked.
Beauty (1:52:47)
Walker explores the concept of beauty:
- Argues beauty is not universal but dependent on history and cultural context
- Suggests the adaptation beauty confers goes beyond sexual selection to social dynamics
- Compares the richness of beauty to the expressive power of language
She emphasizes how beauty and aesthetics can be used to shape social interactions and power dynamics.
Language (1:59:08)
Walker discusses her unique perspective on language:
- Views words as objects with their own ontology, separate from what they describe
- Argues language and internal representations are approximations of reality
- Enjoys "playing" with language to push boundaries of understanding
She suggests: "There's a lot that's happening behind language...I think just recognizing that there's a lot that's happening behind language is really important."
Computation (2:05:50)
Walker challenges conventional views on computation:
- Argues computation is not fundamental to the universe, but a product of life
- Suggests we mistake our ability to build computers with assuming the world is inherently computational
- Proposes computation is at the "top" of reality, not the base
She critiques efforts to show physics or chemistry are "Turing universal," arguing this always requires an agent to set up the system.
Consciousness (2:15:37)
Walker offers her perspective on consciousness:
- Suggests consciousness emerges from our nature as temporally extended objects
- Argues our "inner space" comes from the vast amount of time bundled up in our causal structure
- Proposes consciousness and intelligence may not be separate from the general phenomenon of life
She emphasizes the need for a testable theory of consciousness before we can make definitive claims about machine consciousness.
Artificial Life (2:24:28)
Walker discusses artificial intelligence and its relation to life:
- Views AI as part of the ongoing evolution of life and technology, not a separate species
- Suggests large language models are like a "genetic system for language"
- Argues against viewing AI in isolation, emphasizing its integration with human society
She cautions against narratives that pit humanity against AI, advocating for a more integrated view of technological development.
Free Will (2:48:21)
Walker proposes a unique perspective on free will:
- Argues free will emerges from being a deterministic structure in a random background
- Suggests our ability to select possible futures comes from the vast causal structure bundled within us
- Proposes free will operates over time, not instantaneously
She argues this view of free will is compatible with both determinism and the experience of choice.
Conclusion
Sarah Walker's wide-ranging discussion with Lex Fridman challenges many conventional ideas about life, consciousness, and the nature of reality itself. Her proposal to view life as a planetary-scale phenomenon structured across vast stretches of time offers a radical new perspective on some of science's deepest questions. While many of her ideas remain speculative, they provide thought-provoking new angles on longstanding problems in physics, biology, and philosophy. Walker's work exemplifies the kind of interdisciplinary, big-picture thinking that may be necessary to tackle the most fundamental mysteries of our existence.